输入一个圆半径r,当r>=0时,计算并输出圆的面积和周长,否则,输出提示信息。

#include #define PI 3.14 int main(void) { double r ,area , girth; printf("please input r:\n"); scanf("%lf",&r); if (r>=0) { area =PI*r*r; girth =2*PI*r ; printf("the area is %.2f\n", area); printf("the girth is %.2f\n", girth);} else printf("Input error!\n"); return 0; } .