根据输入的直径值计算圆形的圆周和面积

计算圆周长和面积的公式。

圆周 = 2 * p * r ； 面积 = p * r , 这里 r 是直径

参考以下代码：

#include <stdio.h>

int main(void)
{
  float radius = 0.0f;                  // The radius of the table
  float diameter = 0.0f;                // The diameter of the table
  float circumference = 0.0f;           // The circumference of the table
  float area = 0.0f;                    // The area of the table
  float Pi = 3.14159265f;

  printf("Input the diameter of a circle:");
  scanf("%f", &diameter);               // Read the diameter from the keyboard

  radius = diameter/2.0f;               // Calculate the radius
  circumference = 2.0f*Pi*radius;       // Calculate the circumference
  area = Pi*radius*radius;              // Calculate the area

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