Use #if to check condition - C Preprocessor

C examples for Preprocessor:Preprocessor Operators

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Introduction

The general form of #if is 

#if constant-expression
    statement sequence
#endif

If the constant expression is true, the code that is between it and #endif is compiled.

The #endif directive marks the end of an #if block. For example:

The following code displays the message on the screen because MAX is greater than 99.

The expression that follows the #if is evaluated at compile time. It can contain only previously defined identifiers and constants, no variables may be used.

Demo Code

#include <stdio.h>

#define MAX 100//from   www.j ava  2 s  .  com
int main(void)
{
#if MAX>99
   printf("Compiled for array greater than 99.\n");
#endif
   printf("outside.\n");
   return 0;
}

Result


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