Linux Hub

IF-ELSE

2011-04-06T11:05:00.000+05:30

The simplest of the decision making in a programming language is if-else.
But before this we need to go inside the operators used for comparison.

#include<stdio.h>
int main(){
int i = 10;
printf("%d %d %d",i>20, i< 20; i ==20);
}

Answer is:
0 1 0

This thing you won't find in most of the books. When a comparison fails then it is replaced by 0 otherwise by 1. In the above example when i>20 proves to be failed, then we have found 0 as the output. Isn't it amazing, how the things are done in a simple manner.

Working example.

#include<stdio.h>

int main(){

int i = 10;

if(i<5)
printf("i is greater than 5\n");

else
printf("i is less than 5\n");

}

Output: i is greater than 5.

C Programming - Part 5

2011-02-22T17:48:00.000+05:30

Increment/Decrement Operator with example.

int main(){
     int i=10,j;
   j=++i;
     printf("%d\n",j,i);
   j=i++;
    printf("%d\n",j,i);

}

$ gcc test.c
./a.out
11 11
11 12

C Programming - Part 4

2011-02-07T12:52:00.004+05:30

Working with C Operators

There are some basic but important things that every learner of C should know .
These are--
• Add plenty of comments using (/* */ or // )
• Good layout,
  it should be not like this :
      main( ) {printf("Hello World\n");}
• Use meaningful variable names
• Initialize your variables
• Use parentheses to avoid confusion as:
      a=(10.0 + 2.0) * (5.0 - 6.0) / 2.0

       Common variable types

int -   stores integers
(-32767 to +32768)-- for 16 bit machine
(-2147483647 to + 2147483648)--  for 32-bit machine
(-9223372036854775807 to 9223372036854775808)- for 64 bit machine

unsigned int – range upto 0 to 65535 for 16 bit machine
0 to 4294967296-- for 32- bit machine
0 to 18446744073709551616--   for 64 bit machine

char – holds 1 byte of data (-127 to 128)
unsigned char – holds 1 byte (0 to +255)
long – usually double int (signed)
unsigned long – positive double int
float – floating point variable
double – twice of a floating point variable
Note: local, global and static variables

                                 printf function arguments

• printf (“%d”,i);

Usual variable    type                   Display
%c                      char single character
%d (%i) int signed integer
%e (%E) float or double      exponential format
%f float or double      signed decimal
%g (%G) float or double      use %f or %e as required
%o int unsigned octal value
%p pointer              address stored in pointer
%s array of char sequence of characters
%u int unsigned decimal
%x (%X) int unsigned hex value

                                     Operators

+     addition
-          subtraction
* multiplication
/          division
%    mod or remainder (e.g., 2%3 is 2), also called 'modulo'
<<    left-shift (e.g., i<<j is i shifted to the left by j bits)
>>    right-shift
&    bitwise AND
|    bitwise OR
^    bitwise exclusive-OR
&& logical AND (returns 1 if both operands are non-zero; else 0)
||         logical OR (returns 1 if either operand is non-zero; else 0)
<    less than (e.g., i<j returns 1 if i is less than j)
>        greater than
<= less than or equal
>= greater than or equal
== equals
!=      does not equal

Increment and Decrement Operators

  ++ Increment operator
   -- Decrement Operator

  k++ or k--          (Post-increment/decrement)
k = 10;
x = k++;            // sets x to 10, then increments k to 11

  ++k or --k         (Pre-increment/decrement)
k = 10;
x = ++k;    // increments k to 11 and then sets x to the
   // resulting value, i.e., to 11

We can check these increment and decrement operator into our small tricky programs and can check the value .Till next time try it into the programs .
In next post we will try these programs.

Thanks

Er.Surender Sharma

linux Kernel Developer

C Programming - Part 3

2011-02-07T11:10:00.003+05:30

Structure of a ‘C’ program
This is the structure of program which shows how it looks like.

      pre-processor directives
      global declarations
      function prototypes
      main( )
      {
      local variables to function main ;
      statements associated with function main ;
      }
      f1( )
      {
      local variables to function f1 ;
      statements associated with function f1 ;
      }
      f2( )
      {
      local variables to function f2 ;
      statements associated with function f2 ;
      }

Structure of my first ‘C’ program

   /* This is
      a comment */
   // This is a one-line comment

   # include <stdio.h> /* includes header files */
int main( ) /* Must have a main function. First function executed */
   {
   printf ("Hello World!"); /* stdio functions */
   }

After making this program we need to compile it.One of the compiler we are using is gcc compiler . gcc compiler is best compiler for C programs.The full form of gcc is GNU Compiler Collection .

To use this compiler try as follows:-

cmd prompt>gcc test.c -o test
The prompt we are using id linux prompt.
test.c is the name of the file where you have saved your program
test will be the name of our output compiled file i.e executable file or binary file.
we can run our program as
cmd prompt> ./test

if we are not giving the output file name then by default it creates the a.out output file .

Description of our basic program is as follows:-

#(hash) is the Preprocessor directives and lines included in the code of our programs are not program statements but directives for the preprocessor. These lines are always preceded by (#). The preprocessor is executed before the actual compilation of code begins, therefore the preprocessor digests all these directives before any code is generated by the statements.
These preprocessor directives extend only across a single line of code. As soon as a newline character is found, the preprocessor directive is considered to be end. No semicolon (;) is expected at the end of a preprocessor directive.

stdio.h-- is the standard input ouput header file and in which all input functions ( scanf ) and all ouput functions (printf) are included. We are including the description of printf function into our current program and also we are giving the parameter value in this printf function as
   printf("Hello world !");

int main ( ) {
}
int-- return type means , main function whose return value is integer .
main ( )-- is the function name .
( ) in the blank braces we give command line arguments to the main function .

printf("Hello world ");---- printf is for printing the output value on the screen .

this is the basic program description .We will start from initial .Then we move forward . We will make it simple to understand .Also we should know that what is written in our program that what is the meaning of each particular keyword . Then only we will be able to get the C skills . So wait for the next step.

Thanks

Er.Surender Sharma

linux Kernel Developer

C Programming - Part 2

2011-02-05T10:15:00.002+05:30

In addition to surender's Last article, I would like to elaborate more on the C Language. Most of the operating systems, which you might have been using in your desktop, servers, mobile phone, mobile TV, portable MP3 players etc. are running the C code. "Kernel" the integral part of the operating system, and it is designed and developed using C programming algorithms. If a person is well versed in C, he/she can do any thing in computer science.

I really appreciate Surender's initiative to teach C Language through this blog. If any of his "student" have any doubt then please don't hesitate putting up your questions.

Wishing you all a very successful C Programming.

C Programming - 1

2011-02-04T18:14:00.004+05:30

Part 1"C is Basic language for learning if you know the C language then you can learn any language but professional C is not in 10 programs . add, mul div, fact programs . C means logical programming or conceptual language .That means you should have clear concept of C i.e. deep knowledge then you will be able to adjust C and in turn any language ,very easily .Also you have to learn the programming concept of C but that does not mean just 10 programs .So we will try to learn more than
so called 10 programs. But before Starting the C language we will check out intro that what is C ? Who has developed the C language ? Who created this ? How it is with us ?"

The programming language C was originally developed by Dennis Ritchie of Bell Laboratories and was designed to run on a PDP-11 with a UNIX operating system.
Although it was originally intended to run under UNIX, there has been a great interest in running it under the MS-DOS operating system on the IBM PC and compatibles. It is an excellent language for this environment because of the simplicity of expression, the compactness of the code, and the wide range of applicability. Also, due to the simplicity and ease of writing a C compiler, it is usually the first high level language available on any new computer, including microcomputers, minicomputers, and mainframes.
C is not the best beginning language because it is somewhat cryptic in nature. It allows the programmer a wide range of operations from high level down to a very low level, approaching the level of assembly language. There seems to be no limit to the flexibility available. One experienced C programmer made the statement, "You can program anything in C", and the statement is well supported by my own experience with the language. Along with the resulting freedom however, you take on a great deal of responsibility because it is very easy to write a program that destroys itself due to the silly little errors that a good Pascal compiler will flag and call a fatal error. In C, you are very much on your own as you will soon find.

Wait for next article on starting programming concept with good skills in deep.This is just the intro part of C.

Thanks

Er.Surender Sharma

linux Kernel Developer

Computer Science v/s IT

2011-02-03T10:56:00.001+05:30

Some time it seems to be weird when any Engineering student has been asked a simple question and they don't answer it properly.
"Difference between IT and Computer Science. ?"
They really don't know the difference. I have asked this question in many Engineering Colleges during my seminar on "Open Source". But I feel pity on the students when they just look at each other and don't give the correct answer . So lets clear this confusion.
Computer science is related to the science which is the base of today's computation. If you look at the Computer Science Engineering Syllabus you will find so many subjects which are the part of Computer's Science e.g. Microprocessor, Operating Systems, Compiler Design, Computer Architecture, C Programming.

IT syllabus will have Java, Web design, .NET, Linux Admin etc. So it's very clear that the IT is mainly a computer application subject and CSE is the the core of the computation. But it's our bad luck that the Engineering Students don't know this easy to understand difference. And to make it worse, Engineering College's lecturer are too unaware of this difference.

So don't get confused while making a selection between IT and CSE.

Welcome to the world of Linux

2011-02-02T13:31:00.004+05:30

Hello friends ,

We have started this knowledge sharing blog of learning the core field i.e. "C" and Linux Kernel ,so we want to share our experience and our problems and solutions and our guidance with all .Those who are keen of sharing knowledge and experience ,they can come to this core field world .It is very interesting field and you will enjoy a lot .

Also , we are also supporting to "Indian IT Technology".We are trying to divert Indian talent into this core field, as a Science Subject. Because in today's scenario every body is going through the built in tools like .Net packages , already built in Java libraries . Do you think that there are engineers who created the Java libraries and .Net type packages and other graphical tools .Then what we are doing ? We are just using their made tools and and we boast ourselves as engineers.

"An Engineer creates the engine . He/She never becomes the Driver of that engine. So don't become the Engineer like a Driver, Become the Engineer like an engine maker ".

You should have guts to invent the engine so that world can use it. Look around and you will find that every engineer is using the US based product and says themselves as software engineer,this is not the engineering,is this ?

In Japan ,China,US and Germany children of age bar between 12-15 years create the games after using these tools. They are just children and we are Engineers . There is no difference between those Children and our Engineers.

So ,get up and become a good Engineer and give your Hands to develop the Indian IT and that will become the real IT.Do not be dependent on USA . If we will not change ourselves then USA will sneeze and we the Indians will get swine flu.

"India has not developed its Operating System and tool in-spite of such huge population and we are dreaming that India is the No.1 in IT field. How can you say this ?
Till now India haven't its " National Identity Card Software " . And we are No.-1 in IT ,what a joke ."

Questions:-

Why we can not be able to develop our own Toolchain , Operating System and our own Hardwares ?

The reasons are :-
1) Our students and youngsters are not taking interest in Science of Computer .
2) They just want to earn money immediately ,only money .
3) They want to use the already built in tools and want to learn just graphical creative tools.
For a minute sit back and think how this tools are created.

Try to become the real Engineers.

Hence,share your knowledge with us.
This article is just for motivating you all and not for humiliating because we always think about our country.That's why we started a movement only in a hope that technologies will be invented in India .
We require your help to make our dream successful.
Hence come and join this Linux Hub and Open Source world because you will be free to do what you want to do ?

You are most welcome to share the knowledge ,start discussion ask questions and even you can answer some questions.

Once again welcome to the world of Linux.

written by :

Er.Surender Sharma

linux Kernel Developer