题解

反手一个命名空间

#include<stdio.h>
#include<iostream>
double PI=3.14159;
namespace circle{
	double zhijin(double r){
    	return r*2;
	}
	double zhouchang(double r){
    	return r*2*PI;
	}
	double mianji(double r){
    	return r*r*PI;
	}
}
using namespace circle;
int main(){
    double r;
    std::cin>>r;
    std::printf("%.4f%c%.4f%c%.4f",zhijin(r),' ',zhouchang(r),' ',mianji(r));//神奇的代码
    return 0;
}