I need to use the number pi in C. How to enter it?

Question

for example y=pi*4?

Answer 1

Well, you know the value of PI, all you have to do is create either a variable or a macro for it.

#include <stdio.h>

#define PI 3.14159265359f
// float PI = 3.14159265359f; // This would work just as fine

int main()
{
    float y = PI * 4.0f;
    printf("y = %f\n", y);
    return 0;
}

Comments

i agree with you since you declared the value of PI as a global var it can be used anywhere in the prorgram

Answer 2

You can also use it directly by adding another library in your code. 

The library is math.h, I will demonstrate it by calculating area of a circle, so it would look like,

#include<stdio.h>

#include<math.h>

int main()

{

      float r;

      printf("Enter the value of radius of circle\n");

      scanf("%f",&r);

      printf("The area of the circle is %f\n",M_PI*r*r);

      return 0;

}

      Hope it helps