C Programming language

C - Language Overview
Why use C?
C was initially used for system development work, particularly the programs that make-up the
operating system. C was adopted as a system development language because it produces code
that runs nearly as fast as the code written in assembly language. Some examples of the use of C
might be −

 Operating Systems
 Language Compilers
 Assemblers
 Text Editors
 Print Spoolers
 Network Drivers
 Modern Programs
 Databases
 Language Interpreters
 Utilities

C Programs
A C program can vary from 3 lines to millions of lines and it should be written into one or more
text files with extension ".c"; for example, hello.c. You can use "vi", "vim" or any other text
editor to write your C program into a file.

This tutorial assumes that you know how to edit a text file and how to write source code inside a
program file.


C - Environment Setup
Try it Option Online
We have set up the C Programming environment on-line, so that you can compile and execute all
the available examples on line. It gives you confidence in what you are reading and enables you
to verify the programs with different options. Feel free to modify any example and execute it on-
line.

,Try the following example using our on-line compiler available at CodingGround.

#include <stdio.h>

int main() {

/* my first program in C */
printf("Hello, World! \n");

return 0;
}

For most of the examples given in this tutorial, you will find a Try it option in our website code
sections at the top right corner that will take you to the online compiler. So just make use of it
and enjoy your learning.

Local Environment Setup
If you want to set up your environment for C programming language, you need the following
two software tools available on your computer, (a) Text Editor and (b) The C Compiler.

Text Editor
This will be used to type your program. Examples of few a editors include Windows Notepad,
OS Edit command, Brief, Epsilon, EMACS, and vim or vi.

The name and version of text editors can vary on different operating systems. For example,
Notepad will be used on Windows, and vim or vi can be used on windows as well as on Linux or
UNIX.

The files you create with your editor are called the source files and they contain the program
source codes. The source files for C programs are typically named with the extension ".c".

Before starting your programming, make sure you have one text editor in place and you have
enough experience to write a computer program, save it in a file, compile it and finally execute
it.

The C Compiler
The source code written in source file is the human readable source for your program. It needs to
be "compiled", into machine language so that your CPU can actually execute the program as per
the instructions given.

The compiler compiles the source codes into final executable programs. The most frequently
used and free available compiler is the GNU C/C++ compiler, otherwise you can have compilers
either from HP or Solaris if you have the respective operating systems.

,The following section explains how to install GNU C/C++ compiler on various OS. We keep
mentioning C/C++ together because GNU gcc compiler works for both C and C++ programming
languages.

Installation on UNIX/Linux
If you are using Linux or UNIX, then check whether GCC is installed on your system by
entering the following command from the command line −

$ gcc -v

If you have GNU compiler installed on your machine, then it should print a message as follows −

Using built-in specs.
Target: i386-redhat-linux
Configured with: ../configure --prefix=/usr .......
Thread model: posix
gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)

If GCC is not installed, then you will have to install it yourself using the detailed instructions
available at http://gcc.gnu.org/install/

This tutorial has been written based on Linux and all the given examples have been compiled on
the Cent OS flavor of the Linux system.


C - Program Structure
Before we study the basic building blocks of the C programming language, let us look at a bare
minimum C program structure so that we can take it as a reference in the upcoming chapters.

Hello World Example
A C program basically consists of the following parts −

 Preprocessor Commands
 Functions
 Variables
 Statements & Expressions
 Comments

Let us look at a simple code that would print the words "Hello World" −

#include <stdio.h>

, int main() {
/* my first program in C */
printf("Hello, World! \n");

return 0;
}

Let us take a look at the various parts of the above program −

 The first line of the program #include <stdio.h> is a preprocessor command, which tells
a C compiler to include stdio.h file before going to actual compilation.
 The next line int main() is the main function where the program execution begins.
 The next line /*...*/ will be ignored by the compiler and it has been put to add additional
comments in the program. So such lines are called comments in the program.
 The next line printf(...) is another function available in C which causes the message
"Hello, World!" to be displayed on the screen.
 The next line return 0; terminates the main() function and returns the value 0.

Compile and Execute C Program
Let us see how to save the source code in a file, and how to compile and run it. Following are the
simple steps −

 Open a text editor and add the above-mentioned code.
 Save the file as hello.c
 Open a command prompt and go to the directory where you have saved the file.
 Type gcc hello.c and press enter to compile your code.
 If there are no errors in your code, the command prompt will take you to the next line and
would generate a.out executable file.
 Now, type a.out to execute your program.
 You will see the output "Hello World" printed on the screen.

$ gcc hello.c
$ ./a.out
Hello, World!

Make sure the gcc compiler is in your path and that you are running it in the directory containing
the source file hello.c.


C - Basic Syntax