c preprocessor error

by

C #error:

The #error is a preprocessor directive in C which is used to display an error if #error directive is found during the code execution and thus stops any further compilation of the code.

Example:

#include<stdio.h>  
#ifndef AGE
#error First define then compile  
#else  
void main()
{  
printf("%d",AGE);  
}  
#endif

Output

error: #error First define then compile