This document discusses three ways to write a C program without using the main function. The first way uses the #define preprocessor directive to replace "begin" with "main". The second way uses the ## token merging operator in a #define to merge the characters "m", "a", "i", and "n" together. The third way uses an argumented macro to define a function called "begin" that serves the same purpose as main.

1. C Program to Write
C Program Without
using Main Function
in 3 ways

2. Run C Program Without Main Function
Conceptually C Program is meaningless without main Function . Every
Program Must have Main Function.
Main Function :
a] It is Entry Point of Every C Program.
b] All Predefined and User-defined Functions are called directly or
indirectly through the main.
c] So C Program Must have Main Function.
But I have decided not to write main and want to run C Program , How ?
We have 3 approaches of Writing C Program without using main().

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#include<stdio.h>
#define begin main
int begin() {
printf("Hello");
return (0);
}
Way 1 : Using #define Preprocessor Directive

4. Way 1 : Using #define Preprocessor Directive
What Preprocessor is doing Here ?
• Save C Program using Extension .C
• Before Program is given to compiler program is processed by
Preprocessor .
• begin main
• Source Program is scanned from Left to Right and from Top
to Bottom and “begin” is replaced by “main”
• So Programmer feels that “He has written Code Without
using Main , but internally begin is already converted into
main”

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#include<stdio.h>
#define begin m##a##i##n
void begin() {
printf("Hello");
}
Way 2 : Using #define Token Merging Operator
Explain ?
• The ‘##‘ operator is called the token pasting or token merging operator.
• That is we can merge two or more characters with it.

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#include<stdio.h>
#define begin m##a##i##n
void begin() {
printf("Hello");
}
Way 3 : Using Argumented Macro