Sunday, 1 January 2012

First program in C

Here is your first c program. Write carefully because C Language is a case sensative language.
#include <>
void main()
printf("Hello World\n");
Press Ctrl +F9 to compile,ALT+F5 to execute your program. If you have any error in your program, you will get the error message, remove your errors and then execute your program you will get the out put.
Hello World
The printf() function prints output to stdout, according to format and other arguments passed to printf(). The string format consists of two types of items - characters that will be printed to the screen, and format commands that define how the other arguments to printf() are displayed.
printf( "Hello World’ );
The scanf() function reads input from stdin, according to the given format, and stores the data in the other arguments. It works a lot like printf(). The format string consists of control characters, whitespace characters, and non-whitespace characters.
void main(void)
int i;
C Program File
All the C programs are writen into text files with extension ".c" for example hello.c. You can use "vi" 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 programming instructions inside a program file.
C Compilers
When you write any program in C language then to run that program you need to compile that program using a C Compiler which converts your program into a language understandable by a computer. This is called machine language (ie. binary format). So before proceeding, make sure you have C Compiler available at your computer. It comes alongwith all flavors of Unix and Linux.
If you are working over Unix or Linux then you can type gcc -v or cc -v and check the result. You can ask your system administrator or you can take help from anyone to identify an available C Compiler at your computer.

About Compilation Stages
Compiling a small C program requires at least a single .c file, with .h files as appropriate. Although the command to perform this task is simply cc file.c, there are 3 steps to obtain the final executable program, as shown:
  1. Compiler Stage: All C language code in the .c file is converted into a lower-level language called Assembly language; making .s files.

  2. Assembler Stage: The assembly language code made by the previous stage is then converted into object code which are fragments of code which the computer understands directly. An object code file ends with .o.

  3. Linker Stage: The final stage in compiling a program involves linking the object code to code libraries which contain certain "built-in" functions, such as printf. This stage produces an executable program, which is named a.out by default.

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