#include<stdio.h> int main(){ float circumference,area,a; float pi=3.14159; // circumference = 2 * pi *a; // area = pi * a * a; /* 要先有数值才能进行计算 */ scanf("%f",&a); circumference = 2 * pi *a; area = pi * a * a; printf("%.6f\n%.6f",circumference,area); }