这段代码为什么就是编译不过？

#include <iostream>
using namespace std;
class demo
{
public:
    demo(){x=0;cout<<"demo的默认构造函数"<<x<<endl;}
    demo(int i){x=i;cout<<"demo的带一个参数的构造函数"<<x<<endl";}
        ~demo(){cout<<"demo的默认析构函数"<<x<<endl;}
    int get(){return x;}
    void set(int i){x=i;}
private:
    int x;
};
    class rectangle
    {
    public:
        rectangle(){x=1000;cout<<"rectangle的默认构造函数"<<x<<endl;}
        rectangle(int i,int j,int k):x(i),width(j),length(k)
        {cout<<"rectangle的带3个参数的构造函数"<<"长方形b的面积为："<<width.get()*length.get()<<endl;}
            ~rectangle(){cout<<"rectangle的默认析构函数"<<x<<endl;}
            int area(){return length.get()*width.get();}
    private:
        int x;
        demo length;
        demo width;
    };
    int main()
    {
        rectangle a(100,200,300);
        return 0;
    }
它出现的错误是：
error C2001: newline in constant
error C2079: 'length' uses undefined class 'demo'
fatal error C1004: unexpected end of file found
完全看不懂什么意思，请高手赐教