We can write c program without using main() function. To do so, we need to use #define preprocessor directive.

The C preprocessor is a micro processor that is used by compiler to transform your code before compilation. It is called micro preprocessor because it allows us to add macros.

A macro is a segment of code which is replaced by the value of macro. Macro is defined by #define directive.

For example:

#define PI 3.14


Here, PI is the macro name which will be replaced by the value 3.14.

Let's see a simple program to print "Hello, World!!!" without main() function.

#include<stdio.h>  
#define start main  
void start()  
{  
   printf("Hello, World!!!");  
}  

Output:

Hello, World!!!