新人学生狗，，求抓臭虫，，实在是卡住了，，不知道怎么改啊哭

#include"iostream"
using namespace std;
const double PI=3.1415926;
double yuan(double x)
{double s;
s=PI *x*x;
return s;
}
double chang(double x,double y)
{
double s;
s=x*y;
return s;
}
double zheng(double x)
{double s;
s=x*x;
return s;
}
int main()
{ int i;
printf("请输入图形类型，圆 1，长方形 2,正方形 3");
cin>>i;
switch(i)
{
case 1:
printf("输入半径：");
double r;
cin>>r;
cout<<PI*r*r<<endl;
break;
case 2:
printf("请输入长宽：")；看这里看这里，，编译显示这里不对
double a,b;
cin>>a>>b;
cout<<a*b<<endl;
break;
case 3:
printf("请输入边长");
double c;
cin>>c;
cout<<c*c<<endl;
break;
}
return 0;
}
低级的程序作业·······，，我是纯渣我造，，，，，求指点，，一丢丢就好，谢谢啦