A C program consists of one or more functions or code modules. These are essentially groups of instructions that are to be executed as a unit in a given order and that can be referenced by a unique name. Each C program must contain a main() function. This is the first function called when the program starts to run. Note that while “main” is not a C keyword and hence not reserved it should be used only in this context.
A C program is traditionally arranged in the following order but not strictly as a rule.
|Function prototypes and global data declarations
|The main() function
Consider first a simple C program which simply prints a line of text to the computer screen. This is traditionally the first C program you will see and is commonly called the “Hello World” program for obvious reasons.
/* This is how comments are implemented in C to comment out a block of text */
// or like this for a single line comment
printf( “Hello World\n” ) ;