Preprocessor Directives in C

 Preprocessor Directives in C

Preprocessor directives are commands used by the preprocessor to perform certain actions before the compilation process. They are preceded by a # symbol and are typically used to include header files or define constants.

#include <stdio.h>

#define PI 3.14159

int main() {

    double radius;

    printf("Enter the radius of a circle: ");

    scanf("%lf", &radius);

    double area = PI * radius * radius;

    printf("Area of the circle: %.2f\n", area);

    return 0;

}

In this example, the #include directive is used to include the standard input/output header file. The #define directive defines a constant PI with the value 3.14159. The constant is then used in the program to calculate the area of a circle.