AICOtutorial

Basic Input ( "cin")

arunoda.wijewantha@gmail.com (Anonymous) — Wed, 21 May 2014 15:46:00 +0000

    The standard input device is usually the keyboard. Handling the standard input in C++ is done by applying the overloaded operator of extraction (>>) on the cin stream. The operator must be followed by the variable that will store the data that is going to be extracted from the stream. For example:

      int age;
      cin >> age;

   The first statement declares a variable of type int called age, and the second one waits for an input from cin (the keyboard) in order to store it in this integer variable.

    cin can only process the input from the keyboard once the RETURN key has been pressed. Therefore, even if you request a single character, the extraction from cin will not process the input until the user presses RETURN after the character has been introduced.

    You must always consider the type of the variable that you are using as a container with cin extractions. If you request an integer you will get an integer, if you request a character you will get a character and if you request a string of characters you will get a string of characters.

// i/o example
#include <iostream>
using namespace std;
int main ()
{
int i;
cout << "Please enter an integer value: ";
cin >> i;
cout << "The value you entered is " << i;
cout << " and its double is " << i*2 << ".\n";
return 0;
}

Please enter an integer value: 702
The value you entered is 702 and its double is
1404.

   The user of a program may be one of the factors that generate errors even in the simplest programs that use cin (like the one we have just seen). Since if you request an integer value and the user introduces a name (which generally is a string of characters), the result may cause your program to misoperate since it is not what we were expecting from the user. So when you use the data input provided by cin extractions you will have to trust that the user of your program will be cooperative and that he/she will not introduce his/her name or something similar when an integer value is requested. A little ahead, when we see the stringstream class we will see a possible solution for the errors that can be caused by this type of user input.

You can also use cin to request more than one datum input from the user:

    cin >> a >> b;

is equivalent to:

   cin >> a;
   cin >> b;

    In both cases the user must give two data, one for variable a and another one for variable b that may be separated by any valid blank separator: a space, a tab character or a newline.

cin and strings

    We can use cin to get strings with the extraction operator (>>) as we do with fundamental data type variables:

      cin >> mystring;

    However, as it has been said, cin extraction stops reading as soon as if finds any blank space character, so in this case we will be able to get just one word for each extraction. This behavior may or may not be what we want; for example if we want to get a sentence from the user, this extraction operation would not be useful.

    In order to get entire lines, we can use the function getline, which is the more recommendable way to get user input with cin:

stringstream

   The standard header file <sstream> defines a class called stringstream that allows a string-based object to be treated as a stream. This way we can perform extraction or insertion operations from/to strings, which is especially useful to convert strings to numerical values and vice versa. For example, if we want to extract an integer from string we can write:

       string mystr ("1204");
       int myint;
       stringstream(mystr) >> myint;

    This declares a string object with a value of "1204", and an int object. Then we use stringstream's constructor to construct an object of this type from the string object. Because we can use stringstream objects as if they were streams, we can extract an integer from it as we would have done on cin by applying the extractor operator (>>) on it followed by a variable of type int.

After this piece of code, the variable myint will contain the numerical value 1204.

// stringstreams
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main ()
{
string mystr;
float price=0;
int quantity=0;
cout << "Enter price: ";
getline (cin,mystr);
stringstream(mystr) >> price;
cout << "Enter quantity: ";
getline (cin,mystr);
stringstream(mystr) >> quantity;
cout << "Total price: " << price*quantity <<
endl;
return 0;
}

Enter price: 22.25
Enter quantity: 7
Total price: 155.75

In this example, we acquire numeric values from the standard input indirectly. Instead of extracting numeric values directly from the standard input, we get lines from the standard input (cin) into a string object (mystr), and the we extract the integer values from this string into a variable of type int (quantity).

    Using this method, instead of direct extractions of integer values, we have more control over what happens with the input of numeric values from the user, since we are separating the process of obtaining input from the user (we now simply ask for lines) with the interpretation of that input. Therefore, this method is usually preferred to get numerical values from the user in all programs that are intensive in user input.

Control Structures2

arunoda.wijewantha@gmail.com (Rangana Jayashanka) — Sat, 26 Apr 2014 05:51:00 +0000

Iteration structures (loops)

Loops have as purpose to repeat a statement a certain number of times or while a condition is fulfilled

The while loop

Its format is:

       while (expression) statement

and its functionality is simply to repeat statement while the condition set in expression is true.
For example, we are going to make a program to countdown using a while-loop:

// custom countdown using while
#include <iostream>
using namespace std;
int main ()
{
int n;
cout << "Enter the starting number > ";
cin >> n;
while (n>0) {
cout << n << ", ";
--n;
}
cout << "FIRE!\n";
return 0;
}

Enter the starting number > 8
8, 7, 6, 5, 4, 3, 2, 1, FIRE!

When the program starts the user is prompted to insert a starting number for the countdown. Then the while loop begins, if the value entered by the user fulfills the condition n>0 (that n is greater than zero) the block that follows the condition will be executed and repeated while the condition (n>0) remains being true. The whole process of the previous program can be interpreted according to the following script (beginning in main):

       1. User assigns a value to n
       2. The while condition is checked (n>0). At this point there are two possibilities:
           * condition is true: statement is executed (to step 3)
           * condition is false: ignore statement and continue after it (to step 5)
       3. Execute statement:
          cout << n << ", ";
          --n;
          (prints the value of n on the screen and decreases n by 1)
       4. End of block. Return automatically to step 2
       5. Continue the program right after the block: print FIRE! and end program.

When creating a while-loop, we must always consider that it has to end at some point, therefore we must provide within the block some method to force the condition to become false at some point, otherwise the loop will continue looping forever. In this case we have included --n; that decreases the value of the variable that is being evaluated in the condition (n) by one - this will eventually make the condition (n>0) to become false after a certain number of loop iterations: to be more specific, when n becomes 0, that is where our while-loop and our countdown end.

Of course this is such a simple action for our computer that the whole countdown is performed instantly without any practical delay between numbers.

The do-while loop

Its format is:

do statement while (condition);

Its functionality is exactly the same as the while loop, except that condition in the do-while loop is evaluated after the execution of statement instead of before, granting at least one execution of statement even if condition is never fulfilled. For example, the following example program echoes any number you enter until you enter 0.

// number echoer
#include <iostream>
using namespace std;
int main ()
{
unsigned long n;
do {
cout << "Enter number (0 to end): ";
cin >> n;
cout << "You entered: " << n << "\n";
} while (n != 0);
return 0;
}

Enter number (0 to end): 12345
You entered: 12345
Enter number (0 to end): 160277
You entered: 160277
Enter number (0 to end): 0
You entered: 0

The do-while loop is usually used when the condition that has to determine the end of the loop is determined within the loop statement itself, like in the previous case, where the user input within the block is what is used to determine if the loop has to end. In fact if you never enter the value 0 in the previous example you can be prompted for more numbers forever.

The for loop

Its format is:

for (initialization; condition; increase) statement;

and its main function is to repeat statement while condition remains true, like the while loop. But in addition, the for loop provides specific locations to contain an initialization statement and an increase statement. So this loop is specially designed to perform a repetitive action with a counter which is initialized and increased on each iteration.

It works in the following way:

      1. initialization is executed. Generally it is an initial value setting for a counter variable. This is executed only once.
      2. condition is checked. If it is true the loop continues, otherwise the loop ends and statement is     skipped (not executed).
      3. statement is executed. As usual, it can be either a single statement or a block enclosed in braces { }.
     4. finally, whatever is specified in the increase field is executed and the loop gets back to step 2.

Here is an example of countdown using a for loop:

// countdown using a for loop
#include <iostream>
using namespace std;
int main ()
{
for (int n=10; n>0; n--) {
cout << n << ", ";
}
cout << "FIRE!\n";
return 0;
}

10, 9, 8, 7, 6, 5, 4, 3, 2, 1, FIRE!

The initialization and increase fields are optional. They can remain empty, but in all cases the semicolon signs between them must be written. For example we could write: for (;n<10;) if we wanted to specify no initialization and no increase; or for (;n<10;n++) if we wanted to include an increase field but no initialization (maybe because the variable was already initialized before).

Optionally, using the comma operator (,) we can specify more than one expression in any of the fields included in a for loop, like in initialization, for example. The comma operator (,) is an expression separator, it serves to separate more than one expression where only one is generally expected. For example, suppose that we wanted to initialize more than one variable in our loop:

       for ( n=0, i=100 ; n!=i ; n++, i-- )
     {
        // whatever here...
     }
This loop will execute for 50 times if neither n or i are modified within the loop:

The break statement

Using break we can leave a loop even if the condition for its end is not fulfilled. It can be used to end an infinite loop, or to force it to end before its natural end. For example, we are going to stop the count down before its natural end (maybe because of an engine check failure?):

// break loop example
#include <iostream>
using namespace std;
int main ()
{
int n;
for (n=10; n>0; n--)
{
cout << n << ", ";
if (n==3)
{
cout << "countdown aborted!";
break;
}
}
return 0;
}

10, 9, 8, 7, 6, 5, 4, 3, countdown aborted!

The continue statement

The continue statement causes the program to skip the rest of the loop in the current iteration as if the end of the statement block had been reached, causing it to jump to the start of the following iteration. For example, we are going to skip the number 5 in our countdown:

// continue loop example
#include <iostream>
using namespace std;
int main ()
{
for (int n=10; n>0; n--) {
if (n==5) continue;
cout << n << ", ";
}
cout << "FIRE!\n";
return 0;
}

10, 9, 8, 7, 6, 4, 3, 2, 1, FIRE!

The goto statement

goto allows to make an absolute jump to another point in the program. You should use this feature with caution since its execution causes an unconditional jump ignoring any type of nesting limitations. The destination point is identified by a label, which is then used as an argument for the goto statement. A label is made of a valid identifier followed by a colon (:).

Generally speaking, this instruction has no concrete use in structured or object oriented programming aside from those that low-level programming fans may find for it. For example, here is our countdown loop using goto:

// goto loop example
#include <iostream>
using namespace std;
int main ()
{
int n=10;
loop:
cout << n << ", ";
n--;
if (n>0) goto loop;
cout << "FIRE!\n";
return 0;
}

10, 9, 8, 7, 6, 5, 4, 3, 2, 1, FIRE!

The exit function

exit is a function defined in the cstdlib library.

The purpose of exit is to terminate the current program with a specific exit code. Its prototype is:

void exit (int exitcode);

The exit-code is used by some operating systems and may be used by calling programs. By convention, an exit code of 0 means that the program finished normally and any other value means that some error or unexpected results happened.

The selective structure: switch

The syntax of the switch statement is a bit peculiar. Its objective is to check several possible constant values for an expression. Something similar to what we did at the beginning of this section with the concatenation of several if and else if instructions. Its form is the following:

switch (expression)
{
case constant1:
group of statements 1;
break;
case constant2:
group of statements 2;
break;
.
.
.
default:
default group of statements
}

It works in the following way: switch evaluates expression and checks if it is equivalent to constant1, if it is, it executes group of statements 1 until it finds the break statement. When it finds this break statement the program jumps to the end of the switch selective structure.

If expression was not equal to constant1 it will be checked against constant2. If it is equal to this, it will execute group of statements 2 until a break keyword is found, and then will jump to the end of the switch selective structure.

Finally, if the value of expression did not match any of the previously specified constants (you can include as many case labels as values you want to check), the program will execute the statements included after the default: label, if it exists (since it is optional).

The switch statement is a bit peculiar within the C++ language because it uses labels instead of blocks. This forces us to put break statements after the group of statements that we want to be executed for a specific condition. Otherwise the remainder statements -including those corresponding to other labels- will also be executed until the end of the switch selective block or a break statement is reached.

For example, if we did not include a break statement after the first group for case one, the program will not automatically jump to the end of the switch selective block and it would continue executing the rest of statements until it reaches either a break instruction or the end of the switch selective block. This makes unnecessary to include braces { } surrounding the statements for each of the cases, and it can also be useful to execute the same block of instructions for different possible values for the expression being evaluated. For example:

switch (x) {
case 1:
case 2:
case 3:
cout << "x is 1, 2 or 3";
break;
default:
cout << "x is not 1, 2 nor 3";
}

Notice that switch can only be used to compare an expression against constants. Therefore we cannot put variables as labels (for example case n: where n is a variable) or ranges (case (1..3):) because they are not valid C++ constants.

If you need to check ranges or values that are not constants, use a concatenation of if and else if statements

Control Structures 1

arunoda.wijewantha@gmail.com (Rangana Jayashanka) — Sat, 26 Apr 2014 05:19:00 +0000

Control Structures

      A program is usually not limited to a linear sequence of instructions. During its process it may bifurcate, repeat code or take decisions. For that purpose, C++ provides control structures that serve to specify what has to be done by our program, when and under which circumstances.

     With the introduction of control structures we are going to have to introduce a new concept: the compound statement or block. A block is a group of statements which are separated by semicolons (;) like all C++ statements, but grouped together in a block enclosed in braces: { }:

    { statement1; statement2; statement3; }

     Most of the control structures that we will see in this section require a generic statement as part of its syntax. A statement can be either a simple statement (a simple instruction ending with a semicolon) or a compound statement (several instructions grouped in a block), like the one just described. In the case that we want the statement to be a simple statement, we do not need to enclose it in braces ({}). But in the case that we want the statement to be a compound statement it must be enclosed between braces ({}), forming a block.

Conditional structure: if and else

     The if keyword is used to execute a statement or block only if a condition is fulfilled. Its form is:

      if (condition) statement

     Where condition is the expression that is being evaluated. If this condition is true, statement is executed. If it is false, statement is ignored (not executed) and the program continues right after this conditional structure. For example, the following code fragment prints x is 100 only if the value stored in the x variable is indeed 100:

     if (x == 100)
       cout << "x is 100";

     If we want more than a single statement to be executed in case that the condition is true we can specify a block using braces { }:

    if (x == 100)
   {
       cout << "x is ";
       cout << x;
   }

    We can additionally specify what we want to happen if the condition is not fulfilled by using the keyword else. Its form used in conjunction with if is:

    if (condition) statement1 else statement2

For example:

      if (x == 100)
      cout << "x is 100";
      else
      cout << "x is not 100";

     Prints on the screen x is 100 if indeed x has a value of 100, but if it has not -and only if not- it prints out x is not 100.

    The if + else structures can be concatenated with the intention of verifying a range of values. The following example shows its use telling if the value currently stored in x is positive, negative or none of them (i.e. zero):

       if (x > 0)
       cout << "x is positive";
       else if (x < 0)
       cout << "x is negative";
       else
       cout << "x is 0";

    Remember that in case that we want more than a single statement to be executed, we must group them in a block by enclosing them in braces { }.

Basic Output("cout")

arunoda.wijewantha@gmail.com (Rangana Jayashanka) — Sat, 26 Apr 2014 05:11:00 +0000

Until now, the example programs of previous sections provided very little interaction with the user, if any at all. Using the standard input and output library, we will be able to interact with the user by printing messages on the screen and getting the user's input from the keyboard
.
C++ uses a convenient abstraction called streams to perform input and output operations in sequential media such as the screen or the keyboard. A stream is an object where a program can either insert or extract character to/from it. We do not really need to care about many specifications about the physical media associated with the stream - we only need to know it will accept or provide characters sequentially.

The standard C++ library includes the header file iostream, where the standard input and output stream objects are declared.

Standard Output (cout)

    By default, the standard output of a program is the screen, and the C++ stream object defined to access it is cout.

    cout is used in conjunction with the insertion operator, which is written as << (two "less than" signs).

      cout << "Output sentence"; // prints Output sentence on screen
      cout << 120; // prints number 120 on screen
      cout << x; // prints the content of x on screen

    The << operator inserts the data that follows it into the stream preceding it. In the examples above it inserted the constant string Output sentence, the numerical constant 120 and variable x into the standard output stream cout. Notice that the sentence in the first instruction is enclosed between double quotes (") because it is a constant string of characters. Whenever we want to use constant strings of characters we must enclose them between double quotes (") so that they can be clearly distinguished from variable names. For example, these two sentences have very different results:

      cout << "Hello"; // prints Hello
      cout << Hello; // prints the content of Hello variable

The insertion operator (<<) may be used more than once in a single statement:

      cout << "Hello, " << "I am " << "a C++ statement";

    This last statement would print the message Hello, I am a C++ statement on the screen. The utility of repeating the insertion operator (<<) is demonstrated when we want to print out a combination of variables and constants or more than one variable:

       cout << "Hello, I am " << age << " years old and my zipcode is " << zipcode;

    If we assume the age variable to contain the value 24 and the zipcode variable to contain 90064 the output of the previous statement would be:

        Hello, I am 24 years old and my zip code is 90064

    It is important to notice that cout does not add a line break after its output unless we explicitly indicate it,therefore, the following statements:

        cout << "This is a sentence.";
        cout << "This is another sentence.";

will be shown on the screen one following the other without any line break between them:

         This is a sentence.This is another sentence.

    even though we had written them in two different insertions into cout. In order to perform a line break on the output we must explicitly insert a new-line character into cout. In C++ a new-line character can be specified as \n (backslash, n):

      cout << "First sentence.\n ";
      cout << "Second sentence.\nThird sentence.";

This produces the following output:

     First sentence.
     Second sentence.
     Third sentence.

Additionally, to add a new-line, you may also use the endl manipulator. For example:

     cout << "First sentence." << endl;
     cout << "Second sentence." << endl;

would print out:

     First sentence.
    Second sentence
.
    The endl manipulator produces a newline character, exactly as the insertion of '\n' does, but it also has an additional behavior when it is used with buffered streams: the buffer is flushed. Anyway, cout will be an unbuffered stream in most cases, so you can generally use both the \n escape character and the endl manipulator in order to specify a new line without any difference in its behavior.

Operators

arunoda.wijewantha@gmail.com (Rangana Jayashanka) — Sat, 26 Apr 2014 04:49:00 +0000

Operators

Once we know of the existence of variables and constants, we can begin to operate with them. For that purpose, C++ integrates operators. Unlike other languages whose operators are mainly keywords, operators in C++ are mostly made of signs that are not part of the alphabet but are available in all keyboards. This makes C++ code shorter and more international, since it relies less on English words, but requires a little of learning effort in the beginning.

You do not have to memorize all the content of this page. Most details are only provided to serve as a later reference in case you need it.

Assignment (=)

The assignment operator assigns a value to a variable.

     a = 5;

This statement assigns the integer value 5 to the variable a. The part at the left of the assignment operator (=) is known as the lvalue (left value) and the right one as the rvalue (right value). The lvalue has to be a variable whereas the rvalue can be either a constant, a variable, the result of an operation or any combination of these. The most important rule when assigning is the right-to-left rule: The assignment operation always takes place from right to left, and never the other way:

   a = b;

This statement assigns to variable a (the lvalue) the value contained in variable b (the rvalue). The value that was stored until this moment in a is not considered at all in this operation, and in fact that value is lost.

Consider also that we are only assigning the value of b to a at the moment of the assignment operation. Therefore a later change of b will not affect the new value of a.

For example, let us have a look at the following code - I have included the evolution of the content stored in the variables as comments:

// assignment operator
#include <iostream>
using namespace std;
int main ()
{
int a, b;     // a:?, b:?
a = 10;    // a:10, b:?
b = 4;               // a:10, b:4
a = b;    // a:4, b:4
b = 7;    // a:4, b:7
cout << "a:";
cout << a;
cout << " b:";
cout << b;
return 0;
}

a:4 b:7

This code will give us as result that the value contained in a is 4 and the one contained in b is 7. Notice how a was not affected by the final modification of b, even though we declared a = b earlier (that is because of the right-toleft rule).

A property that C++ has over other programming languages is that the assignment operation can be used as the rvalue (or part of an rvalue) for another assignment operation. For example:

     a = 2 + (b = 5);
is equivalent to:

    b = 5;
    a = 2 + b;

that means: first assign 5 to variable b and then assign to a the value 2 plus the result of the previous assignment of b (i.e. 5), leaving a with a final value of 7.

The following expression is also valid in C++:

a = b = c = 5;

It assigns 5 to the all the three variables: a, b and c.

Arithmetic operators ( +, -, *, /, % )

The five arithmetical operations supported by the C++ language are:

    + addition
    -        subtraction
   *    multiplication
   /       division
   %       modulo

Operations of addition, subtraction, multiplication and division literally correspond with their respective mathematical operators. The only one that you might not be so used to see is modulo; whose operator is the percentage sign (%). Modulo is the operation that gives the remainder of a division of two values. For example, if we write:

     a = 11 % 3;

the variable a will contain the value 2, since 2 is the remainder from dividing 11 between 3.

Compound assignment (+=, -=, *=, /=, %=, >>=, <<=, &=,^=, |=)

When we want to modify the value of a variable by performing an operation on the value currently stored in that variable we can use compound assignment operators:

expression           is equivalent to

value += increase;       value = value + increase;
a -= 5;    a = a - 5;
a /= b;                                    a = a / b;
price *= units + 1;       price = price * (units + 1);

and the same for all other operators. For example:

// compound assignment operators
#include <iostream>
using namespace std;
int main ()
{
int a, b=3;
a = b;
a+=2; // equivalent to a=a+2
cout << a;
return 0;
}

5

Increase and decrease (++, --)

Shortening even more some expressions, the increase operator (++) and the decrease operator (--) increase or reduce by one the value stored in a variable. They are equivalent to +=1 and to -=1, respectively. Thus:

    c++;
    c+=1;
    c=c+1;

are all equivalent in its functionality: the three of them increase by one the value of c.

In the early C compilers, the three previous expressions probably produced different executable code depending on which one was used. Nowadays, this type of code optimization is generally done automatically by the compiler, thus the three expressions should produce exactly the same executable code.

A characteristic of this operator is that it can be used both as a prefix and as a suffix. That means that it can be written either before the variable identifier (++a) or after it (a++). Although in simple expressions like a++ or ++a both have exactly the same meaning, in other expressions in which the result of the increase or decrease operation is evaluated as a value in an outer expression they may have an important difference in their meaning: In the case that the increase operator is used as a prefix (++a) the value is increased before the result of the expression is evaluated and therefore the increased value is considered in the outer expression; in case that it is used as a suffix (a++) the value stored in a is increased after being evaluated and therefore the value stored before the increase
operation is evaluated in the outer expression. Notice the difference:

Relational and equality operators ( ==, !=, >, <, >=, <= )

In order to evaluate a comparison between two expressions we can use the relational and equality operators. The result of a relational operation is a Boolean value that can only be true or false, according to its Boolean result.

We may want to compare two expressions, for example, to know if they are equal or if one is greater than the other is. Here is a list of the relational and equality operators that can be used in C++:

       ==    Equal to
       !=       Not equal to
        >       Greater than
       < Less than
       >=    Greater than or equal to
       <=    Less than or equal to

Here there are some examples:

       (7 == 5) // evaluates to false.
       (5 > 4) // evaluates to true.
       (3 != 2) // evaluates to true.
       (6 >= 6) // evaluates to true.
       (5 < 5) // evaluates to false.

Of course, instead of using only numeric constants, we can use any valid expression, including variables. Suppose that a=2, b=3 and c=6,

       (a == 5) // evaluates to false since a is not equal to 5.
       (a*b >= c) // evaluates to true since (2*3 >= 6) is true.
       (b+4 > a*c) // evaluates to false since (3+4 > 2*6) is false.
       ((b=2) == a) // evaluates to true.

Be careful! The operator = (one equal sign) is not the same as the operator == (two equal signs), the first one is an assignment operator (assigns the value at its right to the variable at its left) and the other one (==) is the equality operator that compares whether both expressions in the two sides of it are equal to each other. Thus, in the last expression ((b=2) == a), we first assigned the value 2 to b and then we compared it to a, that also stores the the value 2, so the result of the operation is true.

Logical operators ( !, &&, || )

The Operator ! is the C++ operator to perform the Boolean operation NOT, it has only one operand, located at its right, and the only thing that it does is to inverse the value of it, producing false if its operand is true and true if its operand is false. Basically, it returns the opposite Boolean value of evaluating its operand. For example:

        !(5 == 5)    // evaluates to false because the expression at its right (5 == 5) is true.
        !(6 <= 4)            // evaluates to true because (6 <= 4) would be false.
        !true // evaluates to false
        !false // evaluates to true.

The logical operators && and || are used when evaluating two expressions to obtain a single relational result. The operator && corresponds with Boolean logical operation AND. This operation results true if both its two operands are true, and false otherwise.
For example:

        ( (5 == 5) && (3 > 6) ) // evaluates to false ( true && false ).
        ( (5 == 5) || (3 > 6) ) // evaluates to true ( true || false ).

Conditional operator ( ? )

The conditional operator evaluates an expression returning a value if that expression is true and a different one if the expression is evaluated as false. Its format is:

        condition ? result1 : result2

If condition is true the expression will return result1, if it is not it will return result2

        7==5 ? 4 : 3    // returns 3, since 7 is not equal to 5.
        7==5+2 ? 4 : 3    // returns 4, since 7 is equal to 5+2.
        5>3 ? a : b                  // returns the value of a, since 5 is greater than 3.
        a>b ? a : b // returns whichever is greater, a or b.

// conditional operator
#include <iostream>
using namespace std;
int main ()
{
int a,b,c;
a=2;
b=7;
c = (a>b) ? a : b;
cout << c;
return 0;
}

7

In this example a was 2 and b was 7, so the expression being evaluated (a>b) was not true, thus the first value specified after the question mark was discarded in favor of the second value (the one after the colon) which was b, with a value of 7.

Comma operator ( , )

The comma operator (,) is used to separate two or more expressions that are included where only one expression is expected. When the set of expressions has to be evaluated for a value, only the rightmost expression is considered.

For example, the following code:

a = (b=3, b+2);
Would first assign the value 3 to b, and then assign b+2 to variable a. So, at the end, variable a would contain the value 5 while variable b would contain value 3.

Constants

arunoda.wijewantha@gmail.com (Rangana Jayashanka) — Sat, 26 Apr 2014 03:31:00 +0000

Constants

Constants are expressions with a fixed value.

Literals

Literals are used to express particular values within the source code of a program. We have already used these previously to give concrete values to variables or to express messages we wanted our programs to print out, for example, when we wrote:

a = 5;

the 5 in this piece of code was a literal constant.

Literal constants can be divided in Integer Numerals, Floating-Point Numerals, Characters, Strings and Boolean Values.

Integer Numerals

   1776
   707
-273

They are numerical constants that identify integer decimal values. Notice that to express a numerical constant we do not have to write quotes (") nor any special character. There is no doubt that it is a constant: whenever we write 1776 in a program, we will be referring to the value 1776.

In addition to decimal numbers (those that all of us are used to use every day) C++ allows the use as literal constants of octal numbers (base 8) and hexadecimal numbers (base 16). If we want to express an octal number we have to precede it with a 0 (zero character). And in order to express a hexadecimal number we have to precede it with the characters 0x (zero, x). For example, the following literal constants are all equivalent to each other:

    75 // decimal
    0113 // octal
    0x4b // hexadecimal

All of these represent the same number: 75 (seventy-five) expressed as a base-10 numeral, octal numeral and hexadecimal numeral, respectively
.
Literal constants, like variables, are considered to have a specific data type. By default, integer literals are of type int. However, we can force them to either be unsigned by appending the u character to it, or long by appending l:

    75 // int
    75u // unsigned int
    75l // long
    75ul // unsigned long

In both cases, the suffix can be specified using either upper or lowercase letters.

Floating Point Numbers

They express numbers with decimals and/or exponents. They can include either a decimal point, an e character (that expresses "by ten at the Xth height", where X is an integer value that follows the e character), or both a decimal point and an e character:

     3.14159 // 3.14159
     6.02e23 // 6.02 x 10^23
     1.6e-19 // 1.6 x 10^-19
     3.0 // 3.0

These are four valid numbers with decimals expressed in C++. The first number is PI, the second one is the number of Avogadro, the third is the electric charge of an electron (an extremely small number) -all of them approximated- and the last one is the number three expressed as a floating-point numeric literal.

The default type for floating point literals is double. If you explicitly want to express a float or long double numerical literal, you can use the f or l suffixes respectively:

     3.14159L // long double
     6.02e23f // float

Any of the letters that can be part of a floating-point numerical constant (e, f, l) can be written using either lower or uppercase letters without any difference in their meanings.

Character and string literals

There also exist non-numerical constants, like:

    'z'
    'p'
    "Hello world"
    "How do you do?"

The first two expressions represent single character constants, and the following two represent string literals composed of several characters. Notice that to represent a single character we enclose it between single quotes (') and to express a string (which generally consists of more than one character) we enclose it between double quotes (").

When writing both single character and string literals, it is necessary to put the quotation marks surrounding them to distinguish them from possible variable identifiers or reserved keywords. Notice the difference between these two expressions:
     x
    'x'
x alone would refer to a variable whose identifier is x, whereas 'x' (enclosed within single quotation marks) would refer to the character constant 'x'.

Character and string literals have certain peculiarities, like the escape codes. These are special characters that are difficult or impossible to express otherwise in the source code of a program, like newline (\n) or tab (\t). All of them are preceded by a backslash (\). Here you have a list of some of such escape codes:

\n    newline
\r    carriage return
\t tab
\v    vertical tab
\b    backspace
\f form feed (page feed)
\a     alert (beep)
\'        single quote (')
\" double quote (")
\?       question mark (?)
\\        backslash (\)

For example:

    '\n'
    '\t'
    "Left \t Right"
    "one\ntwo\nthree"

Additionally, you can express any character by its numerical ASCII code by writing a backslash character (\) followed by the ASCII code expressed as an octal (base-8) or hexadecimal (base-16) number. In the first case (octal) the digits must immediately follow the backslash (for example \23 or \40), in the second case (hexadecimal), an x character must be written before the digits themselves (for example \x20 or \x4A).

String literals can extend to more than a single line of code by putting a backslash sign (\) at the end of each unfinished line.

   "string expressed in \
     two lines"

You can also concatenate several string constants separating them by one or several blank spaces, tabulators, newline or any other valid blank character:

    "this forms" "a single" "string" "of characters"

Finally, if we want the string literal to be explicitly made of wide characters (wchar_t), instead of narrow characters (char), we can precede the constant with the L prefix:

     L"This is a wide character string"

Wide characters are used mainly to represent non-English or exotic character sets.

Boolean literals

There are only two valid Boolean values: true and false. These can be expressed in C++ as values of type bool by using the Boolean literals true and false.

Defined constants (#define)

You can define your own names for constants that you use very often without having to resort to memory consuming variables, simply by using the #define preprocessor directive. Its format is:

#define identifier value

For example:

#define PI 3.14159
#define NEWLINE '\n'

This defines two new constants: PI and NEWLINE. Once they are defined, you can use them in the rest of the code as if they were any other regular constant, for example:

// defined constants: calculate circumference
#include <iostream>
using namespace std;
#define PI 3.14159
#define NEWLINE '\n'
int main ()
{
double r=5.0; // radius
double circle;
circle = 2 * PI * r;
cout << circle;
cout << NEWLINE;
return 0;
}

31.4159

In fact the only thing that the compiler preprocessor does when it encounters #define directives is to literally replace any occurrence of their identifier (in the previous example, these were PI and NEWLINE) by the code to which they have been defined (3.14159 and '\n' respectively).

The #define directive is not a C++ statement but a directive for the preprocessor; therefore it assumes the entire line as the directive and does not require a semicolon (;) at its end. If you append a semicolon character (;) at the end, it will also be appended in all occurrences within the body of the program that the preprocessor replaces.

Declared constants (const)

With the const prefix you can declare constants with a specific type in the same way as you would do with a variable:
const int pathwidth = 100;
const char tabulator = '\t';
Here, pathwidth and tabulator are two typed constants. They are treated just like regular variables except that their values cannot be modified after their definition.

Strings

arunoda.wijewantha@gmail.com (Rangana Jayashanka) — Sat, 26 Apr 2014 02:56:00 +0000

Introduction to strings

Variables that can store non-numerical values that are longer than one single character are known as strings.

The C++ language library provides support for strings through the standard string class. This is not a
fundamental type, but it behaves in a similar way as fundamental types do in its most basic usage.

A first difference with fundamental data types is that in order to declare and use objects (variables) of this type we
need to include an additional header file in our source code: <string> and have access to the std namespace
(which we already had in all our previous programs thanks to the using namespace statement).

// my first string
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string mystring = "This is a string";
cout << mystring;
return 0;
}

This is a string

As you may see in the previous example, strings can be initialized with any valid string literal just like numerical type variables can be initialized to any valid numerical literal. Both initialization formats are valid with strings:

string mystring = "This is a string";
string mystring ("This is a string");

Strings can also perform all the other basic operations that fundamental data types can, like being declared without an initial value and being assigned values during execution:

// my first string
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string mystring;
mystring = "This is the initial string content";
cout << mystring << endl;
mystring = "This is a different string content";
cout << mystring << endl;
return 0;
}

This is the initial string content
This is a different string content

Variables Data Typese

arunoda.wijewantha@gmail.com (Rangana Jayashanka) — Sat, 26 Apr 2014 02:37:00 +0000

Variables Data Typese

The usefulness of the "Hello World" programs shown in the previous section is quite questionable. We had to write several lines of code, compile them, and then execute the resulting program just to obtain a simple sentence written on the screen as result. It certainly would have been much faster to type the output sentence by ourselves. However, programming is not limited only to printing simple texts on the screen. In order to go a little further on and to become able to write programs that perform useful tasks that really save us work we need to introduce the concept of variable.

Let us think that I ask you to retain the number 5 in your mental memory, and then I ask you to memorize also the number 2 at the same time. You have just stored two different values in your memory. Now, if I ask you to add 1 to the first number I said, you should be retaining the numbers 6 (that is 5+1) and 2 in your memory. Values that we could now for example subtract and obtain 4 as result. The whole process that you have just done with your mental memory is a simile of what a computer can do with two variables. The same process can be expressed in C++ with the following instruction set:

a = 5;
b = 2;
a = a + 1;
result = a - b;

Obviously, this is a very simple example since we have only used two small integer values, but consider that your computer can store millions of numbers like these at the same time and conduct sophisticated mathematical operations with them.

Therefore, we can define a variable as a portion of memory to store a determined value.

Each variable needs an identifier that distinguishes it from the others, for example, in the previous code the variable identifiers were a, b and result, but we could have called the variables any names we wanted to invent, as long as they were valid identifiers.

Identifiers

A valid identifier is a sequence of one or more letters, digits or underscore characters (_). Neither spaces nor punctuation marks or symbols can be part of an identifier. Only letters, digits and single underscore characters are valid. In addition, variable identifiers always have to begin with a letter. They can also begin with an underline character (_ ), but in some cases these may be reserved for compiler specific keywords or external identifiers, as well as identifiers containing two successive underscore characters anywhere. In no case they can begin with a digit.

Another rule that you have to consider when inventing your own identifiers is that they cannot match any keyword of the C++ language nor your compiler's specific ones, which are reserved keywords. The standard reserved keywords are:

asm, auto, bool, break, case, catch, char, class, const, const_cast, continue, default, delete,
do, double, dynamic_cast, else, enum, explicit, export, extern, false, float, for, friend, goto,
if, inline, int, long, mutable, namespace, new, operator, private, protected, public, register,
reinterpret_cast, return, short, signed, sizeof, static, static_cast, struct, switch, template,
this, throw, true, try, typedef, typeid, typename, union, unsigned, using, virtual, void,
volatile, wchar_t, while

Additionally, alternative representations for some operators cannot be used as identifiers since they are reserved words under some circumstances:

and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq

Your compiler may also include some additional specific reserved keywords.

Very important: The C++ language is a "case sensitive" language. That means that an identifier written in capital letters is not equivalent to another one with the same name but written in small letters. Thus, for example, the RESULT variable is not the same as the result variable or the Result variable. These are three different variable identifiers

Fundamental data types

When programming, we store the variables in our computer's memory, but the computer has to know what kind of data we want to store in them, since it is not going to occupy the same amount of memory to store a simple number than to store a single letter or a large number, and they are not going to be interpreted the same way.
The memory in our computers is organized in bytes. A byte is the minimum amount of memory that we can manage in C++. A byte can store a relatively small amount of data: one single character or a small integer (generally an integer between 0 and 255). In addition, the computer can manipulate more complex data types that come from grouping several bytes, such as long numbers or non-integer numbers.

Declaration of variables

In order to use a variable in C++, we must first declare it specifying which data type we want it to be. The syntax to declare a new variable is to write the specifier of the desired data type (like int, bool, float...) followed by a valid variable identifier. For example:

   int a;
   float mynumber;

These are two valid declarations of variables. The first one declares a variable of type int with the identifier a. The second one declares a variable of type float with the identifier mynumber. Once declared, the variables a and mynumber can be used within the rest of their scope in the program.
If you are going to declare more than one variable of the same type, you can declare all of them in a single statement by separating their identifiers with commas. For example:

int a, b, c;

This declares three variables (a, b and c), all of them of type int, and has exactly the same meaning as:

    int a;
    int b;
    int c;

The integer data types char, short, long and int can be either signed or unsigned depending on the range of numbers needed to be represented. Signed types can represent both positive and negative values, whereas unsigned types can only represent positive values (and zero). This can be specified by using either the specifier signed or the specifier unsigned before the type name. For example:

unsigned short int NumberOfSisters;
signed int MyAccountBalance;

By default, if we do not specify either signed or unsigned most compiler settings will assume the type to be signed, therefore instead of the second declaration above we could have written:

int MyAccountBalance;

with exactly the same meaning (with or without the keyword signed)

An exception to this general rule is the char type, which exists by itself and is considered a different fundamental data type from signed char and unsigned char, thought to store characters. You should use either signed or unsigned if you intend to store numerical values in a char-sized variable.

short and long can be used alone as type specifiers. In this case, they refer to their respective integer
fundamental types: short is equivalent to short int and long is equivalent to long int. The following two variable declarations are equivalent:

   short Year;
   short int Year;

Finally, signed and unsigned may also be used as standalone type specifiers, meaning the same as signed int and unsigned int respectively. The following two declarations are equivalent:

   unsigned NextYear;
   unsigned int NextYear;

To see what variable declarations look like in action within a program, we are going to see the C++ code of the example about your mental memory proposed at the beginning of this section:

// operating with variables
#include <iostream>
using namespace std;
int main ()
{
// declaring variables:
int a, b;
int result;
// process:
a = 5;
b = 2;
a = a + 1;
result = a - b;
// print out the result:
cout << result;
// terminate the program:
return 0;
}

4

Do not worry if something else than the variable declarations themselves looks a bit strange to you. You will see the rest in detail in coming sections.

Scope of variable

All the variables that we intend to use in a program must have been declared with its type specifier in an earlier point in the code, like we did in the previous code at the beginning of the body of the function main when we declared that a, b, and result were of type int.

A variable can be either of global or local scope. A global variable is a variable declared in the main body of the source code, outside all functions, while a local variable is one declared within the body of a function or a block.

Global variables can be referred from anywhere in the code, even inside functions, whenever it is after its declaration.

The scope of local variables is limited to the block enclosed in braces ({}) where they are declared. For example, if they are declared at the beginning of the body of a function (like in function main) their scope is between its declaration point and the end of that function. In the example above, this means that if another function existed in addition to main, the local variables declared in main could not be accessed from the other function and vice versa.

Initialization of variables

When declaring a regular local variable, its value is by default undetermined. But you may want a variable to store a concrete value at the same moment that it is declared. In order to do that, you can initialize the variable. There are two ways to do this in C++:

The first one, known as c-like, is done by appending an equal sign followed by the value to which the variable will be initialized:

     type identifier = initial_value ;

For example, if we want to declare an int variable called a initialized with a value of 0 at the moment in which it is declared, we could write:

     int a = 0;

The other way to initialize variables, known as constructor initialization, is done by enclosing the initial value between parentheses (()):

type identifier (initial_value) ;

For example:
   int a (0);

Both ways of initializing variables are valid and equivalent in C++.

// initialization of variables
#include <iostream>
using namespace std;
int main ()
{
int a=5; // initial value = 5
int b(2); // initial value = 2
int result; // initial value
undetermined
a = a + 3;
result = a - b;
cout << result;
return 0;
}

6

C++ Language

arunoda.wijewantha@gmail.com (Rangana Jayashanka) — Sat, 26 Apr 2014 02:10:00 +0000

Introduction

Structure Of a Program

Probably the best way to start learning a programming language is by writing a program. Therefore, here is our
first program:

// my first program in C++
#include <iostream>
using namespace std;
int main ()
{
cout << "Hello World!";
return 0;
}

Hello World!

The first panel shows the source code for our first program. The second one shows the result of the program once compiled and executed. The way to edit and compile a program depends on the compiler you are using. Depending on whether it has a Development Interface or not and on its version. Consult the compilers section and the manual or help included with your compiler if you have doubts on how to compile a C++ console program.

The previous program is the typical program that programmer apprentices write for the first time, and its result is the printing on screen of the "Hello World!" sentence. It is one of the simplest programs that can be written in C++, but it already contains the fundamental components that every C++ program has. We are going to look line by line at the code we have just written:

// my first program in C++

This is a comment line. All lines beginning with two slash signs (//) are considered comments and do not have any effect on the behavior of the program. The programmer can use them to include short
explanations or observations within the source code itself. In this case, the line is a brief description of what our program is.

#include <iostream>

Lines beginning with a hash sign (#) are directives for the preprocessor. They are not regular code lineswith expressions but indications for the compiler's preprocessor. In this case the directive #include <iostream> tells the preprocessor to include the iostream standard file. This specific file (iostream) includes the declarations of the basic standard input-output library in C++, and it is included because its functionality is going to be used later in the program.
using namespace std; All the elements of the standard C++ library are declared within what is called a namespace, the namespace with the name std. So in order to access its functionality we declare with this expression that we will be using these entities. This line is very frequent in C++ programs that use the standard library, and in fact it will be included in most of the source codes included in these tutorials.

int main ()

This line corresponds to the beginning of the definition of the main function. The main function is the point by where all C++ programs start their execution, independently of its location within the source code. It does not matter whether there are other functions with other names defined before or after it - the instructions contained within this function's definition will always be the first ones to be executed in any C++ program. For that same reason, it is essential that all C++ programs have a main function.
The word main is followed in the code by a pair of parentheses (()). That is because it is a function
declaration: In C++, what differentiates a function declaration from other types of expressions are these parentheses that follow its name. Optionally, these parentheses may enclose a list of parameters within them.
Right after these parentheses we can find the body of the main function enclosed in braces ({}). What is contained within these braces is what the function does when it is executed.

cout << "Hello World!";

This line is a C++ statement. A statement is a simple or compound expression that can actually produce some effect. In fact, this statement performs the only action that generates a visible effect in our first program.
cout represents the standard output stream in C++, and the meaning of the entire statement is to insert a sequence of characters (in this case the Hello World sequence of characters) into the standard output stream (which usually is the screen). cout is declared in the iostream standard file within the std namespace, so that's why we needed to include that specific file and to declare that we were going to use this specific namespace earlier in our code.
Notice that the statement ends with a semicolon character (;). This character is used to mark the end of the statement and in fact it must be included at the end of all expression statements in all C++ programs
(one of the most common syntax errors is indeed to forget to include some semicolon after a statement).

return 0;

The return statement causes the main function to finish. return may be followed by a return code (in our example is followed by the return code 0). A return code of 0 for the main function is generally interpreted as the program worked as expected without any errors during its execution. This is the most usual way to end a C++ console program.
You may have noticed that not all the lines of this program perform actions when the code is executed. There were lines containing only comments (those beginning by //). There were lines with directives for the compiler's preprocessor (those beginning by #). Then there were lines that began the declaration of a function (in this case, the main function) and, finally lines with statements (like the insertion into cout), which were all included within the block delimited by the braces ({}) of the main function.
The program has been structured in different lines in order to be more readable, but in C++, we do not have strict rules on how to separate instructions in different lines. For example, instead of

int main ()
{
cout << " Hello World!";
return 0;
}

We could have written:

int main () { cout << "Hello World!"; return 0; }

All in just one line and this would have had exactly the same meaning as the previous code.
In C++, the separation between statements is specified with an ending semicolon (;) at the end of each one, so the separation in different code lines does not matter at all for this purpose. We can write many statements per line or write a single statement that takes many code lines. The division of code in different lines serves only to make it more legible and schematic for the humans that may read it.
Let us add an additional instruction to our first program:

// my second program in C++
#include <iostream>
using namespace std;
int main ()
{
cout << "Hello World! ";
cout << "I'm a C++ program";
return 0;
}

Hello World! I'm a C++ program

In this case, we performed two insertions into cout in two different statements. Once again, the separation in different lines of code has been done just to give greater readability to the program, since main could have been perfectly valid defined this way:

int main () { cout << " Hello World! "; cout << " I'm a C++ program "; return 0; }

We were also free to divide the code into more lines if we considered it more convenient:

int main ()
{
cout <<
"Hello World!";
cout
<< "I'm a C++ program";
return 0;
}

And the result would again have been exactly the same as in the previous examples.
Preprocessor directives (those that begin by #) are out of this general rule since they are not statements. They are lines read and processed by the preprocessor and do not produce any code by themselves. Preprocessor directives must be specified in their own line and do not have to end with a semicolon (;).

Comments

Comments are parts of the source code disregarded by the compiler. They simply do nothing. Their purpose is only to allow the programmer to insert notes or descriptions embedded within the source code.

C++ supports two ways to insert comments:

// line comment
/* block comment */

The first of them, known as line comment, discards everything from where the pair of slash signs (//) is found up to the end of that same line. The second one, known as block comment, discards everything between the /* characters and the first appearance of the */ characters, with the possibility of including more than one line.

We are going to add comments to our second program

/* my second program in C++
with more comments */
#include <iostream>
using namespace std;
int main ()
{
cout << "Hello World! "; // prints Hello
World!
cout << "I'm a C++ program"; // prints I'm a
C++ program
return 0;
}

Hello World! I'm a C++ program

If you include comments within the source code of your programs without using the comment characters combinations //, /* or */, the compiler will take them as if they were C++ expressions,most likely causing one or several error messages when you compile it.

Java Exception Handling

arunoda.wijewantha@gmail.com (Anonymous) — Sat, 05 Apr 2014 16:19:00 +0000

     Exception handling is very impotent in software development. When we are getting user input or work with database, exceptions can be thrown. In this case we want to handle those exceptions correctly. If we forget handled exceptions in our program, it's can be stuck due to the exception. We can handle the exception using throw, throws, try-catch or try-catch-final keywords.


1) throws :-
                       Before throw an exception we tell to the compiler, this part can be throw exception or this is risk area, but we cannot handle the exception using throws keyword. It's mean when the exception is thrown program can be stuck. This keyword helps to success compilation without throw exception.

Eg:-

   import java.io.BufferedReader;
   import java.io.InputStreamReader;
   import java.io.IOException;

   public class excepiton{
   public void test()throws IOException{ // this method can be throw Input output exception
   BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
   System.out.print("Enter the number :- ");
   int s=Integer.parseInt(br.readLine());
   System.out.println("You Entered :-"+s);
   }
   public static void main(String args[])throws IOException{ // if you call method with risk, must use throws keyword for each method, witch call to risk method
   excepiton a=new excepiton();
   a.test();
   }
   }

2) try-catch
   If program throw exception, catch it and handle that exception.

The try statement has this general forms:

   1)
try {
   statement that can throw exceptions
}
catch (exception type identifier){
                                             statement executed when exception is thrown
                                  }

2)
try {
   statement that can throw exceptions
}
catch (exception type identifier){
                                             statement executed when exception is thrown
                                  }
finally {                                                     //optional
statement that are executed whether or not exceptions occur
                                  }

                         3)      in java 7 or later version, can use more than one catch close for each try block

                                  try {
   statement that can throw exceptions
}
catch (exception type identifier){
                                             statement executed when exception is thrown
                                  }
catch (exception type identifier){
                                             statement executed when exception is thrown
                                  }
catch (exception type identifier){
                                             statement executed when exception is thrown
                                  }
...............
...............

finally {                                        //optional
statement that are executed whether or not exceptions occur
                                  }

Eg:-

     public class ExceptionExample {
   int x=4,y=0;
   private int divideByZero (){
   int cal=0;
   try{
   cal=x/y; // exception occur "Divide by zero" (y=0)
   }catch(ArithmeticException e){System.out.println(e.getMessage());}
   finally{
   if (y==0)
   System.out.println("y can't equal to zero ");
   }
   return cal;
   }

   public static void main(String args[]){
   ExceptionExample a=new ExceptionExample();
   System.out.println(a.devideByZero());
   }
   }

output in net beans :-

/ by zero

y cannot equal to zero

   This code can compile without problem. But when you run it, code throw Arithmetic Exception called divide by zero. When exception it occur  at cal=x/y line, program jump catch close and execute it. finally program execute finally close.

3) throw :-
throw keyword is used for generate new exception in java.

throw new EmptyStackException()

Exceptions are objects, so you can't simply throw an EmptyStackException. you must use "new" keyword to create an exception object.
You must use in throw keyword between try-catch or under throws keyword.

How to add CSS3 menu for blogger

arunoda.wijewantha@gmail.com (Anonymous) — Wed, 14 Aug 2013 19:25:00 +0000

When we are blogging, menu is very useful for manage our links and pages. CSS3 menus are helps to improve your blog appearance.

All CSS menus have css code and html code. CSS codes are helps to style menus and html code is used to build stricter of the menu.

Menu html Code :-
   Edit this html code and past it in your blog template HTML/JavaScript Gadget.

   parth:-
   Blgger Dashbord-> Layout -> Add a Gadget -> HTML/JavaScript -> Copy and past html code.


                       <div id='cssmenu'>

                       <!--aicotutorial.com-->

                       <ul>

                           <li><a href="http://www.aicotutorial.com/">Home</a></li>
                            <li class='has-sub '><a href="#">Tutorials</a>

                                <ul>

                                     <li class='has-sub '><a

href="#">Tutorial 1</a>

                                           <ul>

                                                 <li><a

href="#">New Tutorial</a></li>

                                                 <li><a

href="#">New Tutorial</a></li>

                                          </ul>

                                     </li>

                                </ul>

                            </li>

                            <li><a

href="#"

>About Us</a></li>

                            <li><a href=

"http://www.aicotutorial.com/">Aicotutorial</a></li>

                         </ul>                     

                         </div>

Menu html code explain:-

1)
     <ul>
     <li><a href='#'>First</a></li>
   <li><a href='#'>Second</a></li>
   </ul>

   code link this-

2)
      <ul>
   <li class='has-sub '><a

href="#">First</a>

                                <ul>
                                     <li class='has-sub '><a

href="#">Sub First</a></li>
     <li class='has-sub '><a href="#">Sub Second</a></li>
</ul>
   <li><a href="#">Second</a></li>
                           </ul>

   Code like this-

3)

   <ul>
   <li class='has-sub '><a

href="#">First</a>
                                   <ul>
                                       <li class='has-sub '><a

href="#">Sub First</a>

                                   <ul>
                                       <li><a

href="#">Sub Sub First</a></li>
                                       <li><a

href="#">Sub Sub Second</a></li>
                                   </ul>

   </li>
<li class='has-sub '><a href="#">Sub Second</a></li>
   </ul>
   <li><a href="#">Second</a></li>
   </ul>


   Design like this-

4)    Replace # symbol to it's menu tab links.
     <a href="#">Link name</a>

   Eg:- <a href="http://www.aicotutorial.com/">Aicotutorial</a>

Menu CSS code:-

   Copy and past this CSS code in your blogger template.

1) Add CSS code to blogger :-

1) Go to blogger Template

2) Get Backup

3) Add css code between ![CDATA[ ...... ]]>

eg:- ![CDATA[ .bold-Test {font-weight:blod;} ]]>

   How i add CSS Style code to Blogger?

Download CSS code:- Download Link

     #cssmenu ul,
                                       #cssmenu li,
                                       #cssmenu span,
                                       #cssmenu a {
   margin: 0;
   padding: 0;
   position: relative;
                                       }
                                       #cssmenu {
   height: 49px;
   border-radius: 5px 5px 0 0;
   -moz-border-radius: 5px 5px 0 0;
   -webkit-border-radius: 5px 5px 0 0;
   background: #141414;
background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALElEQVQImWMwMrJi+v//PxMDw3+m//8ZoPR/qBgDEhuXGLoeYswhXg8R5gAAdVpfoJ3dB5oAAAAASUVORK5CYII=) 100% 100%;
                                              background: -moz-linear-gradient(top, #32323a 0%, #141414 100%);
                                              background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #32323a), color-stop(100%, #141414));
                                                background: -webkit-linear-gradient(top, #32323a 0%, #141414 100%);
background: -o-linear-gradient(top, #32323a 0%, #141414 100%);
                                                background: -ms-linear-gradient(top, #32323a 0%, #141414 100%);
                                                background: linear-gradient(to bottom, #32323a 0%, #141414 100%);
border-bottom: 2px solid #0fa1e0;
   }
                                         #cssmenu:after,
   #cssmenu ul:after {
   content: '';
   display: block;
   clear: both;
   }
                                         #cssmenu a {
   background: #141414; background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALElEQVQImWMwMrJi+v//PxMDw3+m//8ZoPR/qBgDEhuXGLoeYswhXg8R5gAAdVpfoJ3dB5oAAAAASUVORK5CYII=) 100% 100%;
   background: -moz-linear-gradient(top, #32323a 0%, #141414 100%);
   background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #32323a), color-stop(100%, #141414));
   background: -webkit-linear-gradient(top, #32323a 0%, #141414 100%);
   background: -o-linear-gradient(top, #32323a 0%, #141414 100%);
   background: -ms-linear-gradient(top, #32323a 0%, #141414 100%);
   background: linear-gradient(to bottom, #32323a 0%, #141414 100%);
   color: #ffffff;
   display: inline-block;
   font-family: Helvetica, Arial, Verdana, sans-serif;
   font-size: 12px;
   line-height: 49px;
   padding: 0 20px;
   text-decoration: none;
   }
     #cssmenu ul {
   list-style: none;
   }
     #cssmenu > ul {
   float: left;
   }
     #cssmenu > ul > li {
   float: left;
   }
     #cssmenu > ul > li:hover:after {
   content: '';
   display: block;
   width: 0;
   height: 0;
   position: absolute;
   left: 50%;
   bottom: 0;
   border-left: 10px solid transparent;
   border-right: 10px solid transparent;
   border-bottom: 10px solid #0fa1e0;
   margin-left: -10px;
   }
                                         #cssmenu > ul > li:first-child > a {
   border-radius: 5px 0 0 0;
   moz-border-radius: 5px 0 0 0;
   -webkit-border-radius: 5px 0 0 0;
   }
     #cssmenu > ul > li:last-child > a {
   border-radius: 0 5px 0 0;
   -moz-border-radius: 0 5px 0 0;
   -webkit-border-radius: 0 5px 0 0;
   }
   #cssmenu > ul > li.active a {
   box-shadow: inset 0 0 3px #000000;
   -moz-box-shadow: inset 0 0 3px #000000;
   -webkit-box-shadow: inset 0 0 3px #000000;
   background: #070707; background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALklEQVQImWNQU9Nh+v//PxMDw3+m//8ZkNj/mRgYIHxy5f//Z0BSi18e2TwS5QG4MGB54HL+mAAAAABJRU5ErkJggg==) 100% 100%;
   background: -moz-linear-gradient(top, #26262c 0%, #070707 100%);
   background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #26262c), color-stop(100%, #070707));
   background: -webkit-linear-gradient(top, #26262c 0%, #070707 100%);
   background: -o-linear-gradient(top, #26262c 0%, #070707 100%);
   background: -ms-linear-gradient(top, #26262c 0%, #070707 100%);
   background: linear-gradient(to bottom, #26262c 0%, #070707 100%);
   }
   #cssmenu > ul > li:hover > a {
   background: #070707;
background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALklEQVQImWNQU9Nh+v//PxMDw3+m//8ZkNj/mRgYIHxy5f//Z0BSi18e2TwS5QG4MGB54HL+mAAAAABJRU5ErkJggg==) 100% 100%;
   background: -moz-linear-gradient(top, #26262c 0%, #070707 100%);
   background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #26262c), color-stop(100%, #070707));
   background: -webkit-linear-gradient(top, #26262c 0%, #070707 100%);
   background: -o-linear-gradient(top, #26262c 0%, #070707 100%);
   background: -ms-linear-gradient(top, #26262c 0%, #070707 100%);
   background: linear-gradient(to bottom, #26262c 0%, #070707 100%);
   box-shadow: inset 0 0 3px #000000;
   -moz-box-shadow: inset 0 0 3px #000000;
   -webkit-box-shadow: inset 0 0 3px #000000;
   }
      #cssmenu .has-sub {
   z-index: 1;
   }
      #cssmenu .has-sub:hover > ul {
   display: block;
   }
   #cssmenu .has-sub ul {
   display: none;
   position: absolute;
   width: 200px;
   top: 100%;
   left: 0;
   }
      #cssmenu .has-sub ul li {
   *margin-bottom: -1px;
   }
   #cssmenu .has-sub ul li a {
   background: #0fa1e0;
   border-bottom: 1px dotted #6fc7ec;
   filter: none;
   font-size: 11px;
   display: block;
   line-height: 120%;
   padding: 10px;
   }
   #cssmenu .has-sub ul li:hover a {
   background: #0c7fb0;
   }
     #cssmenu .has-sub .has-sub:hover > ul {
   display: block;
   }
     #cssmenu .has-sub .has-sub ul {
   display: none;
   position: absolute;
   left: 100%;
   top: 0;
   }
     #cssmenu .has-sub .has-sub ul li a {
   background: #0c7fb0;
   border-bottom: 1px dotted #6db2d0;
   }
     #cssmenu .has-sub .has-sub ul li a:hover {
   background: #095c80;
   }

Download full menu code:- download

CSS Font Style Code for Blogger

arunoda.wijewantha@gmail.com (Arunoda) — Tue, 30 Jul 2013 06:18:00 +0000

In the previus lesson i explane how to add CSS style code to blogger. In this lesson i give some CSS font style code for you.

How i add CSS Style code to Blogger?

How i Use CSS Font Style code in Blogger article?

1) Text family -

Code 1 - .exampleserif {

font-family: Times, "Times New Roman", Georgia, serif;

Code 2 - .examplesansserif {

font-family: Verdana, Arial, Helvetica, sans-serif;

}

Code 3 - .examplemonospace {

font-family: "Lucida Console", Courier, monospace;

}

Code 4 - .examplecursive {

font-family: cursive;

}

Code 5 - .examplefantasy {

font-family: fantasy;

}

3) Text Bold,Italic -

Code Bold - .bold-Test {

font-weight:bold;

}

Code Italic - .italic-Test {

font-style:italic;

}

Code Under Line - .underline-Test {

text-decoration:underline;

}

4) Text Colur -

Code 1 - .colur-Text{

color:#00ff00;

}

5) Text Shadow -

Code 1 - .Shadow-Text{
text-shadow: 11px 8px 6px rgba(185, 146, 211, 0.86);

}

Code 2 - .Shadow-Text{

color: white;

font: bold 52px Helvetica, Arial, Sans-Serif;

text-shadow: 1px 1px #fe4902, 2px 2px #fe4902,

3px 3px #fe4902;

-webkit-transition: all 0.12s ease-out;

-moz-transition: all 0.12s ease-out;

-ms-transition: all 0.12s ease-out;

-o-transition: all 0.12s ease-out;

}

.Shadow-Text:hover{

position: relative; top: -3px;

left: -3px;

text-shadow: 1px 1px #fe4902, 2px 2px #fe4902, 3px

3px #fe4902, 4px 4px #fe4902, 5px 5px

#fe4902, 6px 6px #fe4902;

}

6) Text 3D -

Code - .3D{ font-family: Arial, sans-serif; line-height: 1em;

color: #fff9d6; font-weight:bold; font-size: 101px;

text-shadow:0px 0px 0 rgb(231,231,231),1px 1px 0

rgb(216,216,216),2px 2px 0

rgb(202,202,202),3px 3px 0

rgb(187,187,187),4px 4px 0

rgb(173,173,173),5px 5px 0

rgb(158,158,158), 6px 6px 0

rgb(144,144,144),7px 7px 6px

rgba(0,0,0,0.8),7px 7px 1px

rgba(0,0,0,0.5),0px 0px 6px

rgba(0,0,0,.2);

}

1) Add CSS code to blogger :-

1) Go to blogger Template

2) Get Backup

3) Add css code between ![CDATA[ ...... ]]>

eg:- ![CDATA[ .bold-Test {font-weight:blod;} ]]>

2) How i Use CSS Font Style code in Blogger article?

Add css font style to Article Blogger

arunoda.wijewantha@gmail.com (Anonymous) — Tue, 02 Jul 2013 17:46:00 +0000

When we are blogging, we want to present our article (post) nice way. In this case, CSS font styles are acting very important role in blogging. Using the CSS you can add beautiful font to your post.

In proves lesson I explain, how to add CSS font style to your blog template. In this lesson I explain how to use (access) that CSS style code for your article.

To the explain I use below CSS code.

.Three-Dee{

font-family: Verdana, sans-serif;
line-height: 1em;

color: #aaadb3;
font-size: 32px;

text-shadow:0px 0px 0 rgb(157,160,166),1px 0px 0 rgb(144,147,153),2px 0px 0 rgb(131,134,140),3px 0px 0 rgb(117,120,126),4px 0px 0 rgb(104,107,113),5px 0px 0 rgb(91,94,100), 6px 0px 0 rgb(78,81,87),7px 0px 6px rgba(0,0,0,0.95),7px 0px 1px rgba(0,0,0,0.5),0px 0px 6px rgba(0,0,0,.2);}

1) Add the above CSS style code to your blog template. (How to add CSS style code my blog template).

2) Now you can access the above CSS style in your article.

Click new post button in your blogging dashboard to create new post.

3) Type your post.
To the example i create a post like this :-

4) Select in the article witch you want to add style font. Then Copy it.

Eg:- When i want to add style font for Topic in above article (History of Computing) i select this line and copy it.

* You can add CSS font style for single word, only one character, paragraph or full of article witch you want.

5) Click HTML button in your article tool bar.

6) Click CTRL+F buttons in your key board to find this word in your article HTML code. Now open find word

section.

Past above copied word in find filed and click enter to run it.

* In the article html code, It's difficult to find specific word. In this case i used above find method.

7) After past word and click enter to find, you can see highlighted word in your code if you entered word is
can be found.

7) Now use between class="your CSS class name" to your selected word opening tag <span xxxx class="your css class name".

Ex:- I added class="Three dee". Because my above CSS example class name is Three dee.

* If your words in between two or more <span>...</span> tags Insert class="your css class name" code
between all this tags.

8) Finally click Compose button and check the modification is successfully.

      * You can reuse one CSS code same article or different articles.
     * Add different CSS style codes in your template, Then you can use different styles in your
        article(s).

How to add CSS to your blog

arunoda.wijewantha@gmail.com (Arunoda) — Sat, 01 Jun 2013 13:46:00 +0000

   When we try to get style for font or background, It's can do nicely using CSS code. In this reason CSS is very important for us when the blogging.

   In this lesson i used 3D font style CSS code and add it to blogger. That example CSS code is given below-

.Three-Dee{
font-family: Verdana, sans-serif;
line-height: 1em;
color: #aaadb3;
font-size: 32px;
text-shadow:0px 0px 0 rgb(157,160,166),1px 0px 0 rgb(144,147,153),2px 0px 0 rgb(131,134,140),3px 0px 0 rgb(117,120,126),4px 0px 0 rgb(104,107,113),5px 0px 0 rgb(91,94,100), 6px 0px 0 rgb(78,81,87),7px 0px 6px rgba(0,0,0,0.95),7px 0px 1px rgba(0,0,0,0.5),0px 0px 6px rgba(0,0,0,.2);}

   This CSS code's Font Sytle is look Like This

How to add CSS code to Blogger blog?

1) Go to blogger dashboard.

2) Go to Blogger Template Designer in dashboard. It Represent by arrow in above picture.

3) Then go to Advance tab in Template Designer.

4) Scroll down the advance menu and then select Add CSS tab in that menu. It's point using arrow in above picture.

5) Copy and past the CSS code .Three-Dee{....}. Finally CSS code is ok press Apply to Blog button.

Now we are added css code successfully. Then you can use it your Article or Template.

If have any question under this lesson, put a comment below. Thank you......

How to Add a Background Image to Blogger

arunoda.wijewantha@gmail.com (Arunoda) — Thu, 18 Apr 2013 06:04:00 +0000

We can easily add a background image in a blogger blog. If you think upload image and set it to the background, remember an image name and location or you can set blogger background images for your blog background.

1) Go to blogger dashboard and click Template tab.

2) Click background on template.

3) Click Scroll button on the background image box.

4) Then open a new window, Now you can select images and click done or You can click Upload image tab for upload your image from your PC.

5) If you click Upload image tab, you can see this kind of window.

Now click Browse button and select your background photo from your PC.
You can see my uploaded background image is shown Background image box. Now ready to set your image for the background, but if you don't like selecting background image go back and select another one.

6) Background image settings.

*   Alignment - which allows you to set the image to the left, right, top, bottom, etc.
* Tile - The image will be repeated left-right, top-bottem if the screen is very large.
* Scroll with page - So that the background statys fixed while the user scrolls through your blog posts like so.

   My recommended settings -
   * Allgnment - center
         * Tile - Tile
         * don't Scroll with page

7) If your background image and settings are ready, Click Apply to Blog button.

You have successfully added background image, If have any question with this lesson, Use comment for this

Difference between blog and website

arunoda.wijewantha@gmail.com (Anonymous) — Wed, 17 Apr 2013 14:50:00 +0000

This topic is highly search in today's online area. Because most people cannot identify what is the blog and what is the website as well as they cannot identify deference. However bog and website have the same basic structure. Because all those site hosts in web area and mostly use same computer languages to develop. The Blog is a type of a Website, But we can identify some major difference between websie and blog.

Blog	Website
Web log = blog	Site on Web = Website
Based on article(post)	Based on information, publicity, links etc
Normally Home page has 5 or 10 articles	Home page based on informations,links etc
A Blog hosted owners have blog's ownership (Ex. I create a blog using blogger.com, But i haven't any legal ownership for this, blogger.com is the owner of blog.)	A Website owner is a site developer or company. Hosted site owners haven't any ownership of our site.
Simple computer language knowledge only need to develop blog site.	Website developers build the site. Because normally computer language knowledge is must used for develop a website.
Always blog developer tries to get more traffic to his blog.	Customers and fence visit site.
Simple language style for use to blog article.	Advance language style is used for this.
Get visitors feedback about the article using the comment.	You cannot comment on Website area.
A good blog is dally updating. They upload new article dally.	Website isn't updated dally. They upload news sometimes.

How to create a blog with blogger

arunoda.wijewantha@gmail.com (Arunoda) — Tue, 16 Apr 2013 08:16:00 +0000

   Blogger.com is provided totally free blogging chance and it's very easy to create and it required only simple html or programing knowledge.

1) Blogger account is required gmail account. If you haven't any gmail account yet click "Create a new gmail account free" button below.



2)  Then you click this link www.blogger.com.

   If you are not logged your gmail account in the same browser, Enter your gmail address and password in logging form.

After you are logged successfully blogger site or If you are logging your gmail account in same browser when you are clicking blogger.com link it automatically get your email address and redirecting blogger welcome page.

3) Now click Continue to Blogger button. Then open a new window. Now click New Blog button.

4) After the clicked New Blog button you can see the new window about creating a new blog.

Then give your blog name, blog Address(url) and choose a template you like. Finally click Create blog button.

5) If you successfully created a blog site, you can see a page like this

Now click on your blog's name. You can see the blogger dashboard on this page.

6) You haven't any post(article) yet. Now you can click New Post button on top.

After you click that button open post edit page. You can choose a font and size, You can attach pictures if you want and you can create your post easily using this tool.

Finally click publish button to publish your post on your blog site.

7) Finally,If you have successfully created your post, you can see it in the post section in blogger dashboard.

Java Exception

arunoda.wijewantha@gmail.com (Anonymous) — Sun, 10 Mar 2013 13:51:00 +0000

When we write a program, but it's having some error, It's can call exception. So that we want to learn about exception. Its very use full for identifying exception and fixed it.
Exceptions are can be divide into two sub topics. There are compile time exception and run time exception.

Compile Time Exception

This exception is thrown in compile time. Our codes have compile time exception, it's cannot be compilde until it's fixed. When the coding if we forgot brackets, type keyword with spelling mistakes, not used patten, .. etc, that code throw exception in compile time. That exception catches compiler and give an error.

Example:-

You can see the underline in red colour, those are indicate compile errors have in that line. This is a feature in Netbeans. When you try compile this code using command prompt, You can see error like this-

Run time Exception

This exception is cannot catch compiler. In this case we cannot identify this exception till the code is run. When the run time exception is thrown, But we cannot identify where this error have. In this case those type exceptions are more dangerous rather than complete time exceptions. Because compile time exceptions can identify easily.

Example:-

import java.util.Scanner;
        public class ExceptionExample {
public static void main(String[] args) {
                                 Scanner s=new Scanner(System.in);
       System.out.print("Enter the value for x :-");
                                 int x=s.nextInt();
       System.out.print("Enter the value for y :-");
       int y=s.nextInt();
                                 int sum=x+y;
       System.out.println("x+y ="+sum);
   }
          }

         This is a simple example to run time exception.When the code is compiled, it's haven't any errors. When this code is run, it's required value for x and y. You must be give for it any two numbers. When you must give character for it, the code will throw exception at run time. Because we are not using the solution for catch this error in user input.

             You can see we give "s" for second user input. In this case program throws run time exception InputMismatchException.

                            * The First error is we cannot assign "s" for integer variable.
                            * Second one is we cannot add integer and string.

******Next Lesson is about The Exception Handling.******

How to use ArrayList in java

arunoda.wijewantha@gmail.com (Arunoda) — Fri, 15 Feb 2013 07:21:00 +0000

Different between array and ArrayList-

Before we learn about Java Array to access array data structure using Java. Array have fix size (length) and fix structure they cannot grow or shrink. Before we use array, it wants to be declared. Array declaration is required array size. In this reason we must know the array size before we declare the array. In this reason array data structure make a consume sometimes when we are programming. Sometimes we want to use an array, but we cannot identify its size, Java ArrayList is implements for escape this consume.

Introduction ArrayList-

java.lang.Object

             java.util.AbstractCollection<E>
                    java.util.AbstractList<E>
                             java.util.ArrayList<E>

ArrayList is a class and it extends AbstractList and implements the list interface. ArrayList like a drain, Because when we add value, automatically ArrayList grows longer. In this reason array list is very useful for our programmings. Using ArrayList, we can shuffle values, select position and add value, change values or delete values in your choices easily.

ArrayList class Constructors-

   ArrayList()
   ArrayList(collection a)
   ArrayList(int length)

Import ArrayList Class-

   import java.util.ArrayList;

Methods in ArrayList Class-

Return type	Method Name
boolean	add(E e) Apply element end to this ArryLis.
void	add(int index, E element) Select the special position and apply to element to this List.
void	clear() Remove all element in this list.
Object	clone() Show copy of ArrayList instance.
boolean	`contains(Object o)` If this list contains the specified element object returns true.
E	get(int Index) Return element at special position.
boolean	isEmpty() Return true when the list is empty.
E	remove(int Index) Remove the element at specified position .
boolean	remove(Object x) Removes the first occurrence of the specified element from this list, if it is present.
E	set(int Index, E element) Replace the element at the special position using given element.
int	size() Return number of element in this list.
Object[]	toArray() Returns an array containing all of the elements in this list in proper sequence (from first to last element).

         ArrayList class has 20 methods. Most impotent methods only given by the above table. You want to know additional knowledge about it visit- Class ArrayList<E> --> Method Summary

Declare the ArrayList Object-

   ArrayList variableName=new ArrayList();
   or
   ArrayList variableName=new ArrayList(length);

How to access ArrayList class-

        You can access ArrayList class using the above methods given by the table.

First Example ArrayList:-

import java.util.ArrayList;
                 public class arraylist {
                         public static void main(String args[]){
             ArrayList a=new ArrayList();     //declare the ArrayList
                                   String word[]={"Apple","Mango","Graps","Mangus","Orange"};
          // add element using for loop
                                   System.out.println("Input=\n");
                                   for(int i=0;i<word.length;i++){
                                             a.add(word[i]);
                                             System.out.println(i+1+")"+word[i]);
                                   }
         // pring the element using ArrayList
                                   int temp=0;
                                   System.out.println("\nOutput=\n");
                                   while(a.isEmpty()==false){ //when the ArrayLit is empty
                                                System.out.println(a.get(temp)); //print the first element in ArrayList
                                   a.remove(temp);       //Reomve the first element in list,then second element come first

                                   }
                     }
             }

Output-

Discussion-

First we create the ArrayList
Add values to the ArrayList using add(), one by one.
Finally print the ArrayList using the while loop(You can use the clone() for print the ArrayList ).

           How the while loop is working-
                    Create the variable temp and assign it to 0, Because first index is 0.
Check the ArrayList isEmpty using isEmpty() method.
                    Till the isEmpty is return false while loop is working.
                    Print the first element using get() method.
                    Read word was removed using remove() method.
Continue it till the ArrayList return isEmpty() is true.

Second Example ArrayList (with all methods are accessed):-

Do you want to get complete example Java code click this button and download it free and then run arraylist.java file-

Multidimensional array Java

arunoda.wijewantha@gmail.com (Anonymous) — Sun, 09 Dec 2012 19:50:00 +0000

             Multidimensional array is used for insert values in a table format like rows and columns. The Array can have more than one dimension. In the last lesson we discuss about one dimension array.In this lesson discuss about array in more than one dimension, two dimensional,three dimensional... like that.When you want to insert two or more values with relation in an array, it's difficult to do using in singly array.

Ex:- Store the student marks for each student for each subject,

             Table format representation is -

The above example can represent using a two dimensional array. It's can declare, subject and Student No is using dimensions in the array.

Create Multidimensional array Object:-

           Array object can be created in two methods, the first one is using new key word and another one is initializing the contents. 

Using new key word-

           DATATYPE VARIABLENAME [][]....=new DATATYPE[SIZE-OF-FIRST-DIMENSION][SIZE-OF-SECOND-DIMENSION]....; 

Using initializing the content-

           DATATYPE VARIABLENAME [][]....={{{value,value},{value,value..},{{values},{values},..}}};

Create two-dimensional array object:-

       Two dimensional arrays can represent table format. Two dimensional array and three dimensional array are most popular arrays in a multidimensional array. Because when we create up three dimensional arrays, it's more complex. 

Using new key word- 

Structure -

            DATATYPE VARIABLENAME [][]=new DATATYPE[SIZE][SIZE];

Ex:-        

            int array[][]=new int[3][5];

            String names[][]=new String[5][5];

Using initializing the content-

Structure -

            DATATYPE VARIABLENAME [][]={{value,value..},{values,value....},{value...}};           

Ex:- 
            int array[][]={{2,6,3,2},{1,6,9,2},{2,5},{8}};
  
            Above table two dimensional array example is can represent like this -

            char marks[][]={{'A','B','E','C'},{'D','A','E','D'},{'C','C','E','C'},{'A','B','B','B'},{'A','A','A','A'}};

Create three-dimensional array object:-

           
           Three dimensional array declaration is like to two dimensional array declaration,

Using new keyword-

      Structure -
            
           DATATYPE VARIABLENAME [][][]=new DATATYPE[SIZE][SIZE][SIZE];
     
      Ex-
           int names[][][]=new int[2][3][7];

      Using initializing the content-

      Structure-
         
           DATATYPE VARIBLENAME [][][]={{{VALUE},{VALUE}},{{VALUE},{VALUE}},{{VALUE}}}
      **Colors are use for represent array scope 

      Ex-
           int names[][][]={{{2,4,6},{20,4}},{{5,23,64}}};

How to access Array - 

     Values are represented in array index. 

   Structure-         
          VARIABLENAME [INDEX][INDEX]...;
    
    Ex-
       two dimensional array- 
                              array[2][4];
       three dimensional array- 
                              array[3][5][8]; 

     For additional details about this are included in the examples given below.        

Example One-

     public class Test {
                   public static void main(String args[]){
                            System.out.println("    *********www.aicotutorial.com********    ");
                            String array[][]={{"Jack","Mary"},{"Roce","Bill","Boston"},{"wiliam"}};
                            for(int i=0;i<array.length;i++){
                                if(i==0){
                                     System.out.println();
                                     System.out.println("first row......");
                                     for(int j=0;j<2;j++)           
                                          System.out.print(j+" index  -"+array[i][j]+" ,");
                                          }
                                else if(i==1){
                                     System.out.println();
                                     System.out.println("second row......");
                                     for(int j=0;j<3;j++)
                                         System.out.print(j+" index  -"+array[i][j]+" ,");           
                                                  }
                               else{
                                     System.out.println();
                                     System.out.println("third row.......");
                                     for(int j=0;j<1;j++)
                                         System.out.println(j+" index  -"+array[i][j]+" ,");
                                     }
               
                                                                      }
                     }
           }

    Above Java code is represented how to create a two dimensional array and how to access those values using nested for loop. First create a two dimensional array and store values in array declaration time.
Then using for loops print that array. Array index are identified using row and each row column index like array [2][3]=first row 2 index. 

Example Two-

   public class website {
       public static void main(String args[]){
           System.out.println("    *********www.aicotutorial.com********    ");
        
            int array[][]=new int[4][3];         //declare the array    
        
            array[0][0]=1;                      //store the values
            array[0][1]=2;
            array[1][2]=3;
            array[3][0]=4;
            array[2][2]=5;
            array[3][1]=6;
            array[1][1]=7;        
        
            for(int i=0;i<4;i++) {     //print the array using for loop            
                  System.out.println();
                  System.out.println(" row "+i+"......");            
                  for(int j=0;j<3;j++){
                       System.out.println(j+" index  ="+array[i][j]+" ,");            
                  }        
            }
      }
  }
 
   In this example represent two dimensional array. First declare the array. Then store values one by one for each index.

   This example table representation is given below-   

 Index

0

1

2

3

0

1

4

1

2

7

6

2

4

5

Example Three-

     public class website {
         public static void main(String args[]){
              System.out.println("    *********www.aicotutorial.com********    ");
        
              int array[][]=new int[2][];                              //declare the array
        
              array[0]=new int[2];                                    //declare the array index 0
              array[1]=new int[5];                                    //declare the array index 1
        
             array[0][0]=1;                                             //store the values 
             array[0][1]=2;
             array[1][0]=3;
             array[1][1]=4;
             array[1][2]=5;
             array[1][3]=6;
             array[1][4]=7;
        
             for(int i=0;i<array.length;i++){                       //print the array
                if(i==0){
                   System.out.println();
                   System.out.println("first row......");            
                   for(int j=0;j<2;j++){
                       System.out.println(j+" index  ="+array[i][j]+" ,");                
                   }
                }
                else{
                   System.out.println();
                   System.out.println("second row......");                
                   for(int j=0;j<5;j++){
                      System.out.println(j+" index  ="+array[i][j]+" ,");                    
                   }
                }
            }         
        }        
    }

  This example shows that how to create arrays with different length for each index.

Table representation is -

Java array

arunoda.wijewantha@gmail.com (Anonymous) — Sat, 06 Oct 2012 16:47:00 +0000

We learned about the variables before. Variables are used to store a value. One variable can store only one value. When you want to store 10 values in same data type, you want to declare 10 variables for it.

Example- When you want to store 10 numbers in Integer data type, you want to declare the 10 Integer data type variables.

int firstNo,secondNo,thirdNo,forthNo,fifthNo,sixthNo,seventhNo,eighthNo, ninthNo,tenthNo;

Now you think when you want to store 100 data's in same data type, above code is not suitable for that, because we want to declare 100 variables for that.

In this reason Java was introduced an array for minimizing this nuisance.

Array

The Array is a data structure, it can hold multiple values of the same data type. The array is allowed to store primitive and reference data types.

Array have a fixed size. The array size (length) an array is established when the array is created. Array index start with zero and its end is changed on our needs.

Structures of the array-

DATATYPE NAME[];

DATATYPE[] NAME;

DATATYPE[] NAME1,NAME2,...; (Both are same data type)

Arrays are declared using enclosing square brackets.

Example- 1) int value[];
2) String[] name;
3) byte[] fName,sName,tName;
4) Text[] memoryAd;
5) int max[],min;

The brackets can be change either before name or after the name. You can declare the arrays in a single statement like that, int[] value1,value2; those arrays are in same data type.

Creating array object-

   Array object can be created in two methods, one is using new key word and another one is initializing the contents.

int value[]=new value[7];

We declare the integer type array and give size is 7.

String giveName[]={"Soro","Jack","Rose"};

We declare the String type array and give values for Soro,Jack and Rose, array is automatically generated size is 3.

Accessing array-

After the array is initialized, you can access this array using subscript expression ([]).

The structure-

ARRAYNAME [subscript];

The array is initialized using an index. We give this index between the brackets. The index is start with zero.

Example-

giveName[0]; //output="Soro"


We have already declared the giveName array, We give valued Soro,Jack and Rose for it. Now we get giveName[0] position. its output is Soro.

Change the array elements-

First type array name and brackets, then give index witch you want to change in brackets. Finally type the new value and assign it.


Example-

giveName[2]="Boston";

We give the word "Rose" for 3 positions to giveName array.
Now we replace the word "Rose" to the word "Boston".


Example-

import java.util.Scanner;
class Test{
int getValue;
String names[];
Scanner s=new Scanner(System.in); //create Scanner object

void getUserInput(){ //declare the getUserInput method
System.out.print("How many names do you want to add =");
getValue=s.nextInt();
names=new String[getValue];
}

void accessRound(){ //declare the accessRound method
for(int i=0;i<names.length;i++){
System.out.print("Enter the "+(i+1)+" name =");
names[i]=s.next();
}
}

void print(){ //declare the print method
for(int i=0;i<names.length;i++){
System.out.println((i+1)+" name is = "+names[i]);
}
}

public static void main(String[] args) {
Test a=new Test(); //create the Test class object
a.getUserInput();
a.accessRound();
a.print();
}
}

Discussion-

void getUserInput(){} -

This method declares for getting user input to identify the array size. Then create an array object is using this value for array size.

   void accessRound(){} -
This method is used for getting names to the array. We declare the for loop and give boolean Expression for i<names.length. names.length same to the names array size, It's passed an integer value.

  void print(){} -
This method is used for print names array. We create for loop and check the variable i is less than to the names array length. Then declare the print statement and print array using for loop.

Inheritance and Polymorphism

arunoda.wijewantha@gmail.com (Anonymous) — Fri, 05 Oct 2012 08:46:00 +0000

In the Last lesson we discuss about Abstraction and Encapsulation. Now we discuss about Inheritance and Polymorphism.

Inheritance

Concept of the inheritance

One class object inheritance the data or behaviors with other classes objects. We can implement this using classes.

In this example, Vehicle class is a Supper class and others are sub classes. We extend Vehicle class for other classes. Then you can access one method in all this classes.

Polymorphism

When we are coding, we use different operations, But this single operation can have different behaviors in different object, We call it for Polymorphism.

Example-

class Dongle{

void dataTransferSpeed();
}

The dongle data transfer speed is change time to time. Polymorphism is allowed different forms of the same service to be defined. We can implement the Polymorphism is using Overloading and Overriding.

Overloading-
You can create methods in same name with using different parameter types.

Overriding -
When you create one class in super class and sub class type (like above picture example), you can use same methods withing same parameter type in those classes.

Abstraction and Encapsulation

arunoda.wijewantha@gmail.com (Anonymous) — Thu, 04 Oct 2012 20:37:00 +0000

Before you were leaned what are the classes and object. Now we discuss additional information about Object Oriented Concepts.

There are few basic concepts underling the object oriented programming.

* Abstraction

* Encapsulation

* Inheritance

* Polymorphism

Each discussion focuses on how these concepts relate to the real world. In this lesson we discuss about the Abstraction and Encapsulation.

Abstraction

Process of defining a data type, often call abstract data type. This data type refers to, providing only essential information to the outside word and hiding their background details and abstract is a design concept on which we only declare functionality doesn't define it because we don't know about them at design point.

We can implement abstract is using either class or interface.

An abstract class-

* Defined to be extend sub classes.
* abstract keyword is used for definition

abstract class Car{

abstract int speed(){}
abstract boolean break(){}
abstract void handling(){}

}

Encapsulation

Encapsulation is a protective barrier that prevents the code and data being randomly accessed by other code defined outside the class. Encapsulation is achieved by using modifiers. Modifiers are the keywords, that determine of a Class, Method or Variable.

1) Access modifiers- * Private
* Public
* Protected
* Default

2) Static modifiers

3) Abstract modifiers

4) Final modifiers

5) Synchronized modifiers

6) Volatile modifiers

7) Native modifiers

Private modifiers-

Example-

private class School{

private int stydentNo;
private void learning(){}
}

  class, variable and method are modified using private keyword. It's mean this class can't be access other classes, even sub classes. This class variables and methods are can only accessible by the class they are defined in.

Public modifiers-

Example-

   public class Car(){

public float temp;
public void speed(){}
}

This class is liked transparent. Anyone can access this class variables and methods. This class can be accessed by any other object.

Protected modifiers-

Example-

   protected class Tree(){

protected int age;
protected boolean health(){

return illness;
}
}

This means that protected class variables and methods have visibility only limited to subclass.

Default modifiers-

Example:-

class Man{
int age;
void running(){}
void sleeping(){}
}

There are no actual keywords used for this example for modify.
We call for it default modifier.

Static modifiers-

Example-

class Cal{

static int value;
public static int sum(){}
}

Static modifiers do not use any instance variables of any object of the class they are defined in. It's take all the data from parameters and compute something from those parameters. When the variable is declared as once regardless of how many objects are instantiated.

Abstract modifier-

Example-

abstract class computer{

abstract double voltage;

private abstract double process(){}

}

One class can have create one or more abstract methods or variables, to declare the abstract classes variables or methods, use abstract keyword front of this. Abstract class can't be directly use new operator since their complete implementation is undefined. Abstract constructors or abstract static methods are not allowed in java programming.

Final modifier-

Example-

final int lastValue=64;

When you are used final modifier for the methods or variables, It's cannot be override moreover.

Synchronized modifiers-

Example-

public synchronized class Car{}

Used to specify that a method is thread safe. In a multi threaded environment like java,it's possible to have many different paths of execution running through the same code.

If you have more than one of your threads running at the same time that access shared objects, it may cause your object to be in an inconsistent state.

Volatile modifiers-

  Volatile modifier is used to the variables, It's can be changed unexpectedly by other parts of the program. May be modified by asynchronous threads.

Native modifiers-

Example-

native double apple();

Native modifier have no body, It's totally deferrante other methods. The native modifier is never used with classes, constructors or variables.

Java BufferedReader- Get user input

arunoda.wijewantha@gmail.com (Anonymous) — Wed, 03 Oct 2012 15:07:00 +0000

In this lesson we learn how to get user input from user. The Last lesson we discussed how to get user input using Scanner class, now we discuss how to get user input using BufferedReader class.

BufferedReader class is already defined in java.io package. We want to import BufferedReader and InputStreamReader classes to create BufferedReader object.

Import BufferedReader and InputStreamReader Classes-

   import java.io.BufferedReader;
import java.io.InputStreamReader;

  We use this import statements above the class body. BufferedReader and InputStreamReader classes are already defined in java.io package, So we can import this class. Then we can access this class for our requirements.


Create a BufferedReader object-

  Before we are learned how to create object. Now we create object using BufferedReader class.

BufferedReader bf=new BufferedReader(new InputStreamReader(System.in));


BufferedReader bf is variable which reference data type. System.in is input stream it means that scanner will take input from console.

Structure of the BufferedReader -

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

class Test{

public static void main(String args[]){

try{

BufferedReader bf=new BufferedReader(new InputStreamReader(System.in);

String StrValue=bf.readLine();

}catch(IOException e){System.out.println(e);}

}

First we import BufferedReader, InputStreamReader, IOException classes. IOException class is import for catch exceptions, We'll learn about this sectors in the exception handling lesson.

Then we create BufferedReader object. This class is intended to about an InputStream, this is liked a bridge from byte streams to character streams.

readLine(); is the method in BufferedReader class. It's return the String type values.try catch is used for catch exceptions when the errors are occurring at run time.

Example-

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

class Test{

String marks1,marks2,marks3;

String subject="Maths",name1,name2,name3;

double nMks1,nMks2,nMks3;

double max,min,sum,avg;

void getValue() throws IOException{

BufferedReader bf=new BufferedReader(new InputStreamReader(System.in));

System.out.print("Enter first name - ");

name1=bf.readLine();

System.out.print("Enter second name- ");

name2=bf.readLine();

System.out.print("Enter third name - ");

name3=bf.readLine();

System.out.print("Enter the "+name1+"'s "+subject+" marks -");

marks1=bf.readLine();

System.out.print("Enter the "+name2+"'s "+subject+" marks -");

marks2=bf.readLine();

System.out.print("Enter the "+name3+"'s "+subject+" marks -");

marks3=bf.readLine();

}

void getSuccess(){

nMks1=Double.parseDouble(marks1);

nMks2=Double.parseDouble(marks2);

nMks3=Double.parseDouble(marks3);

}

void cal(){

sum=nMks1+nMks2+nMks3;

avg=sum/3;

if(nMks1<nMks2){

if(nMks2<nMks3){

max=nMks3;

min=nMks1;

}

else{

max=nMks2;

if(nMks1>nMks3)

min=nMks3;

else

min=nMks1;

}

else{

if(nMks1<nMks3){

max=nMks3;

min=nMks2;

}

else{

max=nMks1;

if(nMks2>nMks3)

min=nMks3;

else

min=nMks2;

}

void printValues(){

System.out.println("\n\n\nName Subject Marks");

System.out.println(name1+" "+subject+" "+marks1);

System.out.println(name2+" "+subject+" "+marks2);

System.out.println(name3+" "+subject+" "+marks3);

System.out.println("\n");

System.out.println("Maximum marks ="+max);

System.out.println("Minimum marks ="+min);

System.out.println("Summation marks ="+sum);

System.out.println("Average marks ="+avg);

}

public static void main(String[] args) {

Test a=new Test();

try {

a.getValue();

a.getSuccess();

a.cal();

a.printValues();

} catch (IOException e) {

System.out.println(e.getMessage());

}

Discussion-

getValue-

We declared BufferedReader object and all input statements in this method. Input command is used six times in this method.

getSuccess-

We have used readLine(); method for get values via BufferedReader. readLine method is returned the values in String data type, But we can't do any mathematical operations via String data type. In this reason we convert this String data type values to double.

ex:-

VARIABLENAME=Double.parseDouble(STRINGVARIABLE);

We can use this code for Integers, floats and double data types. Replace int,float or double data type for the word VARIABLENAME and replace String data type variable name for the word STRINGVARIABLE, then you can get double,int or float data type via String variable.

cal-

This method is used for get mathematical expressions.

We calculate maximum value, minimum value, summation and average using this method.

Java Scanner-get user Input

arunoda.wijewantha@gmail.com (Anonymous) — Mon, 01 Oct 2012 19:30:00 +0000

Get user input using Scanner

   Before we learned java programs, those we got inputs in programs. There are number of ways have to get user inputs in java. Scanner and BufferedReader are some of them.

In this lesson we learn how to get user input from user. Scanner class is already build in java.util package. We can import java.util.Scanner class and create Scanner object. Scanner is allowed to input all primitive data type values and String data type values.

Import Scanner class to java program -

We use import statement above the class body.

import java.util.Scanner;

Create a Scanner object -

Before we are learned how to create object. Now we create object is using Scanner class.


Scanner s=new Scanner(System.in);

Scanner s is a variable which reference data type. System.in is input stream it means that scanner will take input from console.

Get values -

We have created Scanner object. When you want to get values in program, we want to call applicable methods using this object.

If you want to get - byte data type value - nextByte();
Request the next input as a byte

- Short data type value - nextShort();

Request the next input as a Short

- Integer data type value - nextInt();

Request the next input as an Integer

- float data type value - nextFloat();

Request the next input as a float

- double data type value - nextDouble();

Request the next input as a double

- String data type value - next();

Request the next complete token from this

scanner and returns it as a String a token

is usually ended by white space such as a

blank or line break

- String data type value - nextLine();

Request the rest of the current line,

excluding any line separator at the end

Example -

import java.util.Scanner;

class Test{

String firstName,secondName,thirdName;

int firstAge,secondAge,thirdAge;

void getValue(){ //declare the getValue method

Scanner b=new Scanner(System.in);

System.out.print("Enter first Name -");

firstName=b.nextLine();

System.out.print("Enter second Name -");

secondName=b.nextLine();

System.out.print("Enter third Name -");

thirdName=b.nextLine();

System.out.print("Enter first Age -");

secondAge=b.nextInt();

System.out.print("Enter second Age -");

firstAge=b.nextInt();

System.out.print("Enter third Age -");

thirdAge=b.nextInt();

}

void printData(){ //declare the printData method

System.out.print("\n\nFirst name ="+firstName+" his/her age ="+firstAge+"\n"+"Second name ="+secondName+" his/her age ="+secondAge+"\n"+"Third name ="+thirdName+" his/her age ="+thirdAge); //use \n for get new line

}

public static void main(String[] args) {

Test a=new Test(); //create object

a.getValue(); //call getValue method

a.printData(); //call print method

}

Discussion -

We create getValue and printData methods in this example. Then We declare the Scanner object in getValue method. printData method is used for print values, We created single print statement and give all values. \n is used for get new line in this statement.

When this program is running, first print the word Enter first Name. Then cursor is blinding but program is not running beyond.

It mean is now program is request the input. Program is not run beyond give value for it. program request three names and three ages for that names like that.

After the execute getValue method then execute printData method. In that time program execute print statement.