#include<iostream>
using namespace std;
                                                                               
int main() 
{       
	int i;
	const double pi=3.1415926;
	cout<<"请输入以下计算编号：1，长方形面积 。2，圆的面积。3，正方形的面积。\n";
	cin>>i;
	if (i>=3&&i<=0)
		cout<<"你TM在玩我？！只能输入1到3的任一整数"<<endl;
	switch(i)
	{
	case 1:
      double a,b;
	  cout<<"请输入长方形的长和宽\n";	
	  cout<<"长=";
	  cin>>a ;
	  cout<<endl;
	  cout<<"宽=";
	  cin>>b ;
	  cout<<endl;
	  cout<<"长方形的面积为："<<endl;
	  cout<<a*b<<endl;
	case 2:
		double r;
	    cout<<"请输入圆的半径r\n";
		cin>>r;
	    cout<<"半径为"<<r<<"的圆的面积为"<<r*r*pi<<endl;
	case 3:
	  double c;
	  cout<<"请输入正方形的周长c.\n"<<"c="<<endl;
	  cin>>c;
	  cout<<"周长为"<<c<<"正方形的面积为"<<(c/4)*(c/4)<<endl;                                                                           
	  break;
	}
	return 0;
	
}