1 #include<iostream>
 2 #define PI 3.14159265358979
 3 using namespace std;
 4 
 5 float r;
 6 float s;
 7 
 8 void Circle()
 9 {
10     cout<<"请输入半径"<<endl;
11     cin>>r;
12     s=PI*r*r;
13 }
14 
15 void main()
16 {
17     Circle();
18     cout<<"圆的面积为："<<s<<endl;
19 }