C Programming Tutorial
Description
In the C Programming Language, the #if directive allows for conditional compilation. The preprocessor evaluates an expression provided with the #if directive to determine if the subsequent code should be included in the compilation process.
The #if preprocessor directive evaluates the expression or condition. If condition is true, it executes the code otherwise #elseif or #else or #endif code is executed.
Syntax:
#if expression
//code
#endif
Syntax with #else:
#if expression
//if code
#else
//else code
#endif
Syntax with #elif and #else:
#if expression
//if code
#elif expression
//elif code
#else
//else code
#endif
Note
- The #if directive must be closed by an #endif directive.
C #if example
Let's see a simple example to use #if preprocessor directive.
#include <stdio.h>
#include <conio.h>
#define NUMBER 0
void main() {
#if (NUMBER==0)
printf("Value of Number is: %d",NUMBER);
#endif
getch();
}
Output:
Value of Number is: 0
Let's see another example to understand the #if directive clearly.
#include <stdio.h>
#include <conio.h>
#define NUMBER 1
void main() {
clrscr();
#if (NUMBER==0)
printf("1 Value of Number is: %d",NUMBER);
#endif
#if (NUMBER==1)
printf("2 Value of Number is: %d",NUMBER);
#endif
getch();
}
Output:
2 Value of Number is: 1
Example
The following example shows how to use the #if directive in the C language:
/* Example using #if directive */
#include <stdio.h>
#define WINDOWS 1
int main()
{
printf("C programming is a great ");
#if WINDOWS
printf("Windows ");
#endif
printf("resource.\n");
return 0;
}
Here is the output of the executable program:
C programming is a great Windows resource.
