这代码错在哪，我真的找不出来

Question

#include
using namespace std;
class Rectangle
{
private:
int width,length;
public:
Rectangle(int a,int b)
{
width=a;
length=b;
}
void set_rectangle(int w,int l)
{width=w;length=l;}
int area();
int perimeter();
}
int Rectangle::area()
{
return(width*length);
}
int Rectangle::perimeter()
{
return(2*(width+length));
}
int main()
{
Rectangle r(12,4);
cout<<"this rectangle's area is "<<r.area()<<",perimeter is "<<r.perimeter();
r.set_rectangle(2,4);
cout<<"the new rectangle's area is "<<r.area()<<",perimeter is "<<r.perimeter();
return 0;
}

Answer 1

1. #include 这个后面没有头文件
2. 类定义没有结束符 ;