在scanf中读取数据的格式说明符

在%ld和%lf格式说明符中，l是小写的L。必须始终在使用＆接收输入值变量的名称前面加上前缀。

#include <stdio.h>

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 * 3.14159f * radius;
  area = 3.14159f * radius * radius;

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