使用#define定义命名常量

#include <stdio.h>
#define PI   3.14159f  // Definition of the symbol PI

int main(void){
  float radius = 0.0f;
  float diameter = 0.0f;
  float circumference = 0.0f;
  float area = 0.0f;

  printf(Input the diameter of a circle:);
  scanf(%f, &diameter);

  radius = diameter/2.0f;
  circumference = 2.0f*PI*radius;
  area = PI*radius*radius;

  printf(\nThe circumference is %.2f. , circumference);
  printf(\nThe area is %.2f.\n, area);
  return 0;
}