c常量形式是什么 C 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 table:"); 
      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; 
    } 

#include <stdio.h> 

int main(void) 
{ 
  float diameter = 0.0f;                    // The diameter of a table 
  float radius = 0.0f;                      // The radius of a table 
  const float Pi = 3.14159f;                // Defines the value of Pi as fixed 
  
  printf("Input the diameter of the table:"); 
  scanf("%f", &diameter); 
  
  radius = diameter/2.0f; 
  
  printf("nThe circumference is %.2f.", 2.0f*Pi*radius); 
  printf("nThe area is %.2f.n", Pi*radius*radius); 
  return 0; 
}