类的写法（二）

#include<iostream>
using namespace std;
const float PI=3.141593;
const float A=35;
const float B=20;
class circle{
public:
float C(float a);
float S(float b);
private:
float r;
};
float circle::C(float a){
r=a;
return 2*PI*r;
}
float circle::S(float b){
r=b;
return PI*r*r;
}
main(){
float x;
circle pool;
circle poolrim;
cout<<"please input a r值：\n";
cin>>x;
cout<<"栅栏的造价为：\t"<<A*pool.C(x)<<endl;
cout<<"过道的造价为：\t"<<B*(pool.S(x+3)-pool.S(x))<<endl;
return 0;
}