My C Programmings

Type of Storage class "register"

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A 'register' storage class is very similar to 'auto' storage class except one most important property. All register variable in C stores in CPU not in memory.

Properties of register storage class

(1) In following declaration:

We are only requesting not forcing to compiler to store variable a in CPU.Compiler will decide where to store in the variable 'a'.

(2) A register variable execute faster than other variables because it is stored in CPU so during the execution compiler has no extra burden to bring the variable from memory to CPU.

(3) Since a CPU have limited number of register so it is programmer responsibility which variable should declared as register variable i.e. variable which are using many time should declared as register variable.

(4) We cannot dereference register variable since it has any memory address.

For Example:

(a)

#include<stdio.h>

int main()

{

int *p;

p = &a;

printf("%u",p);

}

Output: Compilation Error

(5) Default initial value of register variable is garbage.

(6) Scope and visibility of register variable is block.

Introduction of Storage class

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In C there are four types of storage class.
they are

1. auto

2. register

3. static

4. extern

Storage class is modifier or qualifier of data types which decides :

1. In which area of memory a particular variable will be stored?
2. What is scope of variable?
3. What is visibility of variable?

Visibility of a variable in C:

Visibility means accessibility. Up to which part or area of a program, we can access a variable, that area of part is known as visibility of that variable.

Scope of a variable in C :

Meaning of scope is to check either variable is alive or dead. Alive means data of a variable has not destroyed from memory. Up to which part or area of the program a variable is alive, that area or part is known as scope of a variable.

In the above figure scope of variable a represented outer red box i.e. it is dead then variable must not be visible.

There are four type of scope in C :

1. Block scope

2. function scope

3. File scope

4. Program scope

This will be clear when all the topics are covered.

Type of Storage class "auto"

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Automatic variables or auto variables are default storage class of local variable. An auto variable cannot be declared globally.

Properties of auto storage class

1 Default initial value of auto variable is garbage.

For example :

#include<stdio.h>

int main()

{

int i;

auto char c;

float f;

printf("%d %c %f",i,c,f);

return 0;

}

Output: Garbage Garbage Garbage

2. Visibility of auto variable is within the block where it has declared.

For example:

(a)

#include<stdio.h>

int main()

{

int a = 10;

{

int a = 20;

printf("%d",a);

}

printf("%d",a);

return 0;

}

Output: 20 10

Explanation:

Visibility of variable a which has declared inside inner has block only within that block.

(b)

#include<stdio.h>

int main()

{

int a = 20;

printf("%d",a);

}

printf("%d",a); // 'a' is not visible here

return 0;

}

Output: Compilation error

Explanation:

Visibility of variable a which has declared inside inner block has only within that block.

3. Scope of 'auto' variable is within the block where it has declared.

For Example:

#include<stdio.h>

int main()

{

int i;

for(i=0;i<4;i++)

{

int a = 20;

printf("%d",a);

a++

}

return 0;

}

Output: 20 20 20 20

Explanation: Variable declared inside the for loop block has only within that block.

After the first iteration variable a becomes dead and it looses it's incremented value. In second iteration variable 'a' is again declared and initialize and so on.

4. From above example it is clear 'auto' variable initialize each time.

5. An 'auto' vriable gets memory at run time.

Data Type Introduction

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Introduction

Every programming language deals with some data. For example to print any message it requires charter or string type of data. To solve any mathematics expression it requires integral as well as real number (floating type) of data. C is very rich in data type. We can broadly divide all data type in C in three categories :

Primitive or fundamental data type
Derived data type
User defined data type

Built-in data types or primitive data types :

int
float
double
char
void

int - data type

int is used to define integer numbers.

{

int count;

Count = 5;

}

float - data type

float is used to define floating point numbers.

{

float Miles;

Miles = 4.6;

}

double - data type

double is used to define BIG floating point numbers.

It reserves twice the storage for the number. On PCs this is likely to be 8 bytes;

{

double Atoms;

Atoms = 25000000;

}

char - data type

char defines characters.

{

char Letter;

Letter = 'a';

}

Derived data types available are

array
pointers
functions

User defined data types

structure
union
enumerations

Derived data types and User defined data types will be explained in next sessions.

Data Type Modifiers

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Modifiers

The data types explained previously have the following modifiers :

short
long
signed
unsigned

The modifiers define the amount if storage allocated to variable. The amount of storage allocated is not cast in stone. ANSI has the following rules:

short int <= int <= long int

float <= double <= long double

What this means is that a 'short int' should assign less than or the same amount of storage as an 'int' and the 'int' should be less or the same bytes than a 'long int'.

What this means in the real word is:

Bytes:

2 short int

2 unsigned short int

4 unsigned int

4 int

4 long int

1 signed char

1 unsigned char

4 float

8 double

12 long double

Ranges

short int -32,768 to +32,767

unsigned short int 0 to +65,535

unsigned int 0 to +65,535

int -32,768 to +32,767

long int -2,147,483,648 to + 2,147,483,647

signed char -128 to +127

unsigned char 0 to +255

float 3.4*10^-38 to 3.4*10^38

double 1.7*10^-308 to +1.7*10^308

Note: One simple way to remember the limits is :

Every 1 byte = 8 bits

so range is form (2^(n-1)) to (2^(n-1))-1

where 'n' is the no. of. bits

e.g.

for int takes 2 bytes

2 bytes = 16 bits

so n = 16

so range is from (2^15) to (2^15)-1

Qualifiers

A type qualifier is used to refine the declaration of a variable, a function, and parameters, by specifying whether:

The value of a variable can be changed. The value of variable must always be read from memory rather than from a register.

Standard C language recognizes the following two qualifiers:

1. const :

The const qualifiers is used to tell C that the variable value can not changed after initialisation.

const float pi = 3.24259;

Now pi cannot be changed at a later time within the program. Another way to define constants is with the # define preprocessor which has the advantage that it does not use any storage.

2. volatile :

The volatile qualifier declares a data type that can have its value changed in ways outside the control or detection of the compiler ( such as a variable updates by the system clock or by another program).

This prevents the compiler from optimizing code referring to the object by storing the objects value in a registered re-reading it from there, rather than from memory, where it may have changed. You will use this qualifier once you will become expert in 'C'. So for now just proceed.

Data Type Example

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Note : As you know size of data types is compiler depended in C. Answer of all question is based upon that compilers whose word sixe is two byte. Just to know you, size of data type in 2 bytes compilers is as follows:

char : 1 byte

int : 2 byte

float : 4 byte

double: 8 byte

Please adjust the answers according to size of data types in your compiler.

1. What will be output when you will execute following C code?

#include<stdio.h>

int main()

{

printf("%d\t",sizeof(6.5));

printf("%d\t",sizeof(90000));

printf("%d",sizeof('A'));

return 0

}

Output :

Turbo C++ 3.0 = 8 4 2

Turbo C++ 4.5 = 8 4 2

Linux GCC = 8 4 4

Visual C ++ = 8 4 4

Explanation :

By default data type of numeric constants is :

6.5 = double

90000 = long int

'A' = char

In C size of data type varies from compiler to compiler.

In TURBO C 3.0 (16 bit compilers) size of :

double is 8 byte

long int is 4 byte

character constant is 2 byte (size of char data type is one byte)

In TURBO C $.5 or Linux GCC compilers (32 bit compilers ) size of :

double is 8 byte

long int is 8 byte

character constant is 2 byte

2. What will be output when you will execute following C code ?

#include<stdio.h>

int main()

{

double num = 5.2;

int var = 5;

printf("%d\t",sizeof(!num));

printf("%d\t",sizeof(var = 15/2));

printf("%d",var);

return 0;

}

Output :

Turbo C++ 3.0 = 2 2 5

Turbo C++ 4.5 = 2 2 5

Linux GCC = 4 4 5

Visual C ++ = 4 4 5

Explanation:

sizeof(Expr) operator always returns the integer value which represents the size of the final value of the expression expr.

Consider on the following expression:

!num

=!5.2

0 is int type integer constant and it size is 2 by in TURBO C 3.0 compiler and 4 in the TURBO C 4.5 and Linux GCC compilers.

Consider on the following expression:

var = 15/2

= var = 7

= 7

7 is int type integer constant.

Any expression which is evaluated inside the sizeof operator. So value of variable 'var' will remain 5 in the printf statement.

3. What will be output when you will execute following C code?

#include<stdio.h>

int main()

{

signed x;

unsigned y;

x = 10 +-10u + 10u +-10;

y = x;

if(x==y)

printf("%d %d",x,y);

else if(x!=y)

printf("%u %u",x,y);

return 0;

}

Output :

Turbo C++ 3.0 = 0 0

Turbo C++ 4.5 = 0 0

Linux GCC = 0 0

Visual C ++ = 0 0

Explanation :

Consider on the expression:

x = 10 +- 10u + 10u +- 10;

10 = it is signed integer constant

10u = it is unsigned integer constant

X = it is signed integer variable.

In nay binary operation of dissimilar data type operand always automatically type casted into the operand of higher data type before performing the operation and result will be higher data type.

As we know operators enjoy higher precedence than binary operators. So our expression is:

x = 10 + (-10u) + 10u + (-10);

= 10 + -10 + 10 + (-10);

Note : Signed is higher data type than unsigned int. So, Corresponding signed value of unsigned 10u is +10

4. What will be output when you will execute following C code?

#include<stdio.h>

int main()

{

volatile int a = 11;

printf("%d",a);

return 0;

}

Output : Connot predict

Explanation:

We cannot predict the value of volatile vriavle because it's value can be changed by nay microprocessor interrupt.

Variables

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Introduction

A variable is just a named area of storage that can hold a single value (numeric or character). The C language demands that you declare the name of each variable that you are going to use and it's type or class, before you actually try to do anything with it.

The Programming language C has Two main Variable Types as following:

Local Variables

Local variables scope is confined within the block or function where it is defined. Local variables must always be defined at the top of a block.

When a local variable is defined it is not initialised by the system, you must initialise it yourself. When execution of the block starts the variable is available and when the block ends the variable 'dies'.

Global Variables

Global variable is defined at the top of the program file and it can be visible and modified by any function that may reference it. Global variables are initialised automatically by the system when you define them !

Every variable in C has it's own name. A variable without any name is not possible in C. Most important properties of variables name are it's unique names. The rules for writing variable name is same as that of identifiers.

Not two variables in C can have same name with same visibility.

For Example:

#include<stdio.h>

int main()

{

int a = 5; //Visibility is within main block

int a = 10; //Visibility is within main block

/* Two variables of same name */

printf("%d",a);

return 0;

}

Output: Compilation error

#include<stdio.h>

int a = 5; // Visibility is in whole program

int main()

{

int a = 10; //Visibility is within main block

/* Two variables of ame name */

printf("%d",a);

return 0;

}

Output: 10

But it is possible that two variable with same name but different visibility.

In this case variable name can access only that variable which is more local.

In C there is not any way to access global variable if any local variable is present of same name.

For Example:

#include<stdio.h>

int main()

{

int a=10; //Visibility within main block

{

a= a+5; //Accessing outer local variable 'a'

int a=20; //Visibility within inner block

a= a+10; //Accessing inner local variable 'a'

printf("%d",a); //Accessing inner local variable 'a'

}

printf("%d",a); //Accessing outer local variable 'a'

return 0;

}

Output: 30 15

Address of a Variable in C

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Location in a memory where a variable stores it's data or value is known as address of variable.

To know address of any variable C has provided a special unary operator & which is known as deference operator or address operator.

It operator is only used with variables not with the constant.

For Example:

#include<stdio.h>

int main()

{

int a = 5;

printf("Address of variable 'a' is :",&a);

return 0;

}

We cannot write: &&a because:

&&a = &(&a) = & (address of variable 'a') = & (a constant number)

And we cannot use address operator with constant.

Important points about address of variables in C:

(1)

Address of any variable in c is an unsigned integer.

It cannot be a negative number.

So in printf statement we should use ' %u ' instead of ' %d ', to print the address of any variable.

Format specifiers:

" %d " : It is used to print signed decimal number.

" %u " : It is used to print unsigned decimal number.

" %x " : It is used to print a number in hexadecimal format using 0 to 9 and a,b,c,d,e,f.

" %X " : It is used to print a number in hexadecimal format using 0 to 9 and A,B,C,D,E,F.

since, if the address of any variable will beyond the range of signed short int it will print a cyclic value.

(2)

To print the address of any variable in hexadecimal number format by printf function we should use ' %x ' or ' %X '.

(3)

A programmer cannot know at which address a variable will store the data. It is decided by compiler or operating system.

(4)

Any two variables in C cannot have same physical address.

(5)

Address of any variable reserve two bytes of memory spaces.

(6)

Address of any variable in C is not integer type so to assign an address to a integral variable we have to type cast the address.

Address arithmetic in C:

(1)

We can subtract address of any two variables.

For Example:

#include<stdio.h>

int main()

{

int a;

int b;

printf("%d",&b-&a);

return 0;

}

(2)

we cannot add, multiply, divide two address.

(3)

We can add or subtract a integer number with address.

(4)

Other operators which can be used with addresses are :

Negation operator : !

Size operator : sizeof

Type casting operator : (Type)

Deference operator : *

Logical operator : && , ||

Examples of Variables

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Example 1 : what will be output of the following C program?

#include<stdio.h>

int main()

{

int goto = 5;

printf("%d",goto);

return 0;

}

Output: Compilation error

Explanation: Invalid variable name 'goto' is keyword in C. Variable name cannot be any of keywords of C language.

Example 2 : What will be output of the following C program?

#include<stdio.h>

int main()

{

int _ = 5;

int __= 10;

int ___;

___ = _ + __;

printf("%d",___);

return 0;

}

Output : 15

Explanation: Variable name can have only underscore.

Example 3 : What will be output of the following C program?

#include<stdio.h>

int main()

{

int abcdefghijklmnopqrstuvwxyz123456789 = 10;

int abcdefghijklmnopqrstuvwxyz123456 = 40;

printf("%d",abcdefghijklmnopqrstuvwxyz123456);

return 0;

}

Output : Compilation error

Explanation: Only first 32 characters are significant in variable name. So compiler will show error : Multiple declaration of identifier abcdefghijklmnopqrstuvwxyz123456.

Example 4 : What will be output of the following C Program?

#include<stdio.h>

int main()

{

int xyz = 20;

int xyz;

printf("%d",xyz);

return 0;

}

Output : Compilation error.

Explanation : Two local variables cannot have same name in same scope.

Example 5 : What will be output of the following C Program?

#include<stdio.h>

int main()

{

int main = 50;

printf("%d", main);

return 0;

}

Output : 50

Explanation : Variable name can be ' main ' because it is not a keyword.

Keywords

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keywords are the reserved words used in programming. Each keywords has fixed meaning and that cannot be changed by user.

For Example:

int money;

Here, int is a keyword that indicates 'money' is of type integer.
As, C programming is case sensitive, all keywords must be written in lower-case. Here is the list of all keywords predefined by ASCII C.

keywords in C Language

auto
double
int
struct
break
else
long
switch
case
enum
register
typeof
char
extern
return
union
continue
for
signed
void
do
if
static
while
default
goto
sizeof
volatile
const
float
short
unsigned

Identifiers

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In 'C' Language any name is called 'identifier'. This name can be variable name, function name, enum constant name, micro constant name, goto label name, any other data type name like structure, union, enum names or typeof name.

Rule 1: Name of identifier includes alphabets, digit and underscore.

Valid name: world,addition21, sum_of_number etc.

Invalid name: factorial#, avg value, display*number etc.

Rule 2: First character of any identifier must be either alphabets or underscore.

Valid name: _calculate, _5, a_, _ etc.

Invalid name: 5_, 10 =_function, 123 etc.

Rule 3: Name of identifier cannot be any keyword of C program.

Invalid name: float, enum etc.

Rule 4: Name of identifier cannot be exactly same as of name of function within the scope of the function.

Example:

#include<stdio.h>

int main()

{

int printf = 5; // don't do this

printf("%d",printf);

return 0;

}

Output: Compilation error

Rule 5: Name of identifier is case sensitive i.e. num and Num are two dirrent variables.

Rule 6: Only first 32 characters are significant of identifier name.

Example:

abcdefghijklmnopqrstuvwxyz123456aba

abcdefghijklmnopqrstuvwxyz123456bcb

abcdefghijklmnopqrstuvwxyz123456czc

All above three identifier names are same because only first 32 characters has meaning. Rest has not any importance.

Rule 7: No two successive underscores are allowed.

Rule 8: identifier name cannot be exactly same as constant name which have been declared in header file of c and you have included that header files.

Header Files

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A header file is a file with extension ' .h ' which contains C function declarations and definitions and to be shared between several source files.

There are two types of header files : The files that the programmer writes and the files that come with your compiler.

You request the use of a header file in your program by including it, with the C preprocessing directive ' #include ' like you have seen inclusion of ' stdio.h ' header file which comes along with your compiler.

Including a header file is equal to copying the content of the header file but we do not do it because it will be very much error-prone and it is not a good idea to copy the content of header file in the source files, specially if we have multiple source file comprising our program.

A simple practice in C program is that we keep all the constants, macros, system wide global variables, and function prototypes in header files and include that header file whenever it is required.

Include syntax

Both user and system header files are included using the preprocessing directive #include. It has following two forms:

#include<file>

This form is used for system header files. It searches for a file named file in a standard list of system directories. You can prepend directories to this list with -I option while compiling your source code.

#include "file"

This form is used for header files of your own program. It searches for a file named file in the directory containing the current file. You can prepend directories to this list with -I option while compiling your source code.

Escape Sequences and Format Specifiers

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Character combinations consisting of a backslash ' \ ' followed by letter or by a combination of digits are called "Escape Sequences". To represent a newline character, single quotation mark, or certain other characters in a character constant, you must use escape sequences. An escape sequence is regarded as a single character and is therefore valid as a character constant.

Escape sequences are typically used to specify actions such as carriage returns and tab movements on terminals and printers. They are also used to provide literal representations of nonprinting characters and characters that usually have special meanings, such as the double quotation mark ( " ).

The following table lists the ANSI escape sequences and what they represent.

List of Escape Sequences

"\a" Audible Bell ( To ring a beep )

"\b" Backspace ( It moves one space back )

"\n" New line ( It moves control to next line )

"\f" From feed ( It moves one page next ) [ It's used in printing the whole copy only ]

"\t" Horizontal Tab ( It moves five spaces of 'Tab' ) [ User can also set 'Tab' space

according his/her requirement ]

"\v" Vertical Tab ( It moves five lines down ) [ It does not work in Turbo-c Compiler ]

"\r" Carriage Return ( It replaces a word or string from the beginning of the other other

string )

[ Ex. printf("\n Kite is beautiful \r Bike"); Will display the output: Bike is beautiful ]

"\'" It displays a single quote

"\"" It displays double quotes

"\?" It displays question mark

"\0" Null character ( It tells us the end of the string and is used in string handling )

Example:

#include<iostream.h>

int main()

{

printf("This\nis\na\ntest\nShe said,\"How are you?\"\n");

}

Output:

This

test

She said,"How are you?"

List of Format Specifiers

%c The character formate specifier.

%d The integer format specifier.

%i The integer format specifier ( same as %d )

%f The floating-point format specifier.

%o The unsigned octal format specifier.

%s The string format specifier.

%u The unsigned integer format specifier.

%x The unsigned hexadecimal format specifier.

%X The unsigned hexadecimal format specifier.

scanf() Function

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How to Read Data From Keyboard Using scanf() Function

Similar to printf() function, scanf() function also uses the %d, %f, %c and other format specifiers to specify the kind of data to be read from the keyboard.

However, it expects the programmer to prefix the address operator '&' to every variable written in the argument list as show below:

int roll;

scanf("%d",$roll);

The above set of statements declares the variable 'roll' of data type 'int', and reads the value for 'roll' from the keyboard. It may be noted that '&' the address operator, is prefixed to the variable 'roll'. The reason for specifying '&' would be discussed later.

Similarly, other format specifiers can be to input data from the keyboard.

Example 1: Write an interactive program that reads the marks secured by a student for four subjects 'Sub1', 'Sub2', 'Sub3' and 'Sub4' the maximum marks of a subject being 100. The program shall compute the percentage of marks obtained by the student.

Solution : The scanf() and printf() functions would be used to do the required task. The required program is as follows :

#include<stdio.h>

main()

{

int sub1,sub2,sub3,sub4;

float percent;

printf("Enter the marks for four subjects :");

scanf("%d %d %d %d", &sub1, &sub2, &sub3, &sub4);

percent = (sub1 + sub2 + sub3 + sub4)/400.00*100;

printf("The percentage = %f", & percent);

}

For input data : 45 56 76 90

The above program computes the percentage and displays the following output :

Outout :

The percentage = 66.750000

printf() Function

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'C' uses printf() and scanf() functions to write and read from I/O devices, respectively. These functions have been declared in the header file called 'stdio.h'

Let us use printf() function to rewrite our first program. The modified program is given below :

#include<stdio.h>

main()

{

printf("This is my first program in C language.");

}

This program displays the following message on the screen:

This is my first program in C language.

In fact, any text written within the pair of quotes ( " " ) is displayed as such by printf() function on the screen.

How to Display Data Using printf() Function

An integer, stored in a variable =, can be displayed on the screen by including a format specifier ( %d ) within a pair of quotes as shown below :

#include<stdio.h>

main()

{

int age=20;

printf("%d",age);

}

The above program does the following:

Declares a variable 'age' of data type 'int'
Initializes 'age to '20', an integer value.
Specifies '%d', a format specifier indicating that an integer is to be displaying by printf() and the data is stored in the variable called 'age'.

It may noted that printf() has two arguments separated by a comma, i.e., format specifier written within quotes and the variable 'age'. It may be further noted that both messages and format specifiers can be included within tha pair of quotes as shown below :

#include<stdio.h>

main()

{

int age=20;

printf("The age of student = %d",age);

}

The above statement would display the following data on the screen :

The age of student = 20

Thus, the text between the quotes has been displayed as such but for ' %d ' , the data stored in the variable 'age' has been displayed.

A float can be displayed on the screen by including a format specifier ' %f ' , within the pair of quotes as shown below:

#include<stdio.h>

main()

{

float rate = 1.5;

printf("The rate of water = %f",rate);

}

Obviously, the above program would produce the following output on display screen :

The rate of water = 1.5

A char be displayed by including a format specifier ' %c ' within the pair of quotes as shown below :

#include<stdio.h>

main()

{

char ch = 'Abhi'

printf("The name of author is = %c",ch);

}

Obviously, the above program would produce the following output on display screen :

The name of author is Abhi

The other specifier which can be used in printf() functions are given on the next session.

Basics

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Functions is block or part of the program. Every C program has at least one function which is main(), and all the most trivial programs can define additional functions.

Example:

#include<stdio.h>

int main() // execution starts from here

{

//statements will be written here

return 0 ;

}

NOTE: When trying on compiler you need to add a statement called getch() before return 0 and header file at the top called #include<conio.h> so as to make output stationary on your computer output window. Otherwise output window will get close in a milliseconds like Flash.

Example:

#include<stdio.h>

#include<conio.h>

int main() //execution start from here

{

//statements will be written here

getch();

return 0;

}

There are Two Types of Functions

Build in Functions

The Functions those are provide by C Language are refers to the Built in Functions. Example printf, scanf that we will discussing details in separate session.

User Defined Functions

But in the other hand the functions those are developed by the user for their programs are know as User Defined Functions. That will be discussed in separate session.

Introduction C Programming

2014-08-08T12:45:00.000+05:30

Every full C program begins inside a function call "main". A function is simply a collection of commands that do "something". The main function is always called when the program first executes. From main, we can call other functions, whether they be written by us or by others or built-in language features. To access the standard functions that comes with your compiler, you need to include a header with #include directive. What this dose is effectively take everything in the header and paste it into your program.

Let's look at a working program:

#include<stdio.h>

int main() /* this is a comment tag */

{

printf("Hello World ! I am Abhi");

return 0; // it is a comment

}

Let's look at the elements of the program. The #include is a "preprocessor" directive thta tells the compiler to put code from the header called stdio.h into our program before actually creating the executable . By including header files, you can gain access to many different functions - both the printf and getchar functions are included in stdio.h

The next important line is int main(). This line tells the compiler that there is a function named main, and that the function returns as integer, hence int. The "curly braces" { and } signal the beginning and end of functions and other code blocks.

The printf function is the standard C way of displaying output on the screen. The quotes tell the compiler that you want to output the literal string as it is (almost).

Finally, at the end of the program, we return a value from main to operating system by using the return statement . This return value is important as it can be used to tell the operating system whether our program succeeded (without any error or bug) or not. A return value of '0' means success.

The final brace closes off the function. You should try compiling this program and running it. You can cut paste the code(but I personally prefer to type it ) into a notepad file, save it as a .c file extension and compile it

Comments In C Program

Everything that is inside /* and */ is considered as a comment in c program and will be ignored by the compiler. You must not include comments within other comments.e.g.

/* this is a /* comment */ inside a comment, which is completely wrong!! */

Your compiler may allow this, but it's not standard C programming.

You may also encounter comments after //. These are C++ comments and while they will be allowed in the next revision of C standard, you shouldn't use them yet. They are more limited that the flexible /* */ comments anyway.