复数类运算符重载，复数加整数计算问题

不知道为什么main函数中的2+z4一直报错，但是main函数是给定的不能改，有人知道怎么改吗，感谢

//友元函数计算2+z
#include<iostream>
using namespace std;

class Cmycomplex
{
public:
    Cmycomplex(double a=0,double b=0);//缺省构造函数 
    void Set(double, double);
    Show();
    Cmycomplex operator+(int&);
    Cmycomplex operator+(Cmycomplex &);//声明运算符+ 重载函数 
    friend Cmycomplex operator+(int &, Cmycomplex &); 
private:
    double real;//复数实部 
    double imag;//复数虚部 
};

Cmycomplex::Cmycomplex(double a, double b)
{
    real = a;
    imag = b;
}

void Cmycomplex::Set(double a, double b)
{
    real = a;
    imag = b;
}

Cmycomplex Cmycomplex :: operator+(Cmycomplex &c2)
{
   return Cmycomplex(real+c2.real,imag+c2.imag);
}

Cmycomplex Cmycomplex::operator+(int&i)
{
  return Cmycomplex(real+i,imag);
}


Cmycomplex operator+(int &m, Cmycomplex &n)
{
    return Cmycomplex(m+n.real,n.imag);
}
Cmycomplex::Show()
{
    if (imag >= 0) cout << '(' <<  real << '+'  << imag << 'i' << ')';
    if (imag < 0) cout << '(' <<  real << "-" << imag << 'i' << ')';
}
//StudybarCommentBegin
int main()
{
    Cmycomplex z1(3,4),z2(7),z3,z4(z1);
    double x,y;
    cin>>x>>y;
    z3.Set(x,y);
    cout<<endl;
    z3=z3+z2;
    z3.Show();
    //int i=2;
    z4=2+z4;
    cout<<endl;
    z4.Show();
    z4=z4+2;
    cout<<endl;
    z4.Show();

} 
//StudybarCommentEnd 

有两种改法：

1. 参数用常量引用：

   Cmycomplex operator+(const int &);
   friend Cmycomplex operator+(const int &, Cmycomplex &); 
   

2. 参数不使用引用：

   Cmycomplex operator+(int);
   friend Cmycomplex operator+(int, Cmycomplex &); 
   

另外Show函数前面需要加个void