C

preprocessors in c#

Directive		Description
#if				#elif
#else			#endif
If				Else if
Else			End if
#define			Symbol define
#undef			Symbol undefine
#error			Generate error
#warning		Generate warning
#line			Set line number
#region			Mark section start
#endregion		Mark section end

C #define preprocessor

#include <stdio.h>
#define PI 3.1415

int main()
{
    float radius, area;
    printf("Enter the radius: ");
    scanf("%f", &radius);

    // Notice, the use of PI
    area = PI*radius*radius;

    printf("Area=%.2f",area);
    return 0;
}

C #define preprocessor

#include <stdio.h>
#define PI 3.1415
#define circleArea(r) (PI*r*r)

int main() {
    float radius, area;

    printf("Enter the radius: ");
    scanf("%f", &radius);
    area = circleArea(radius);
    printf("Area = %.2f", area);

    return 0;
}