大佬们为什么我那样改，下面+符号会提示出错

Question

大佬们为什么我那样改，下面+符号会提示出错

}

在学习重载这章，为啥加了取地址符就不对了，如图。但是如果加法两边都是类对象的话，加不加取地址都对。大佬们解释下，为什么啊，啥时候要加取地址符，啥时候不用呢```

#include<iostream>
using namespace std;
class complex
{
public:
    complex(){ real = 0; image = 0; }

    complex(double r){ real = r; image = 0; }
    complex(double r, double i) :real(r), image(i){}
    friend ostream&operator<<(ostream&, complex&);
    friend complex operator+(complex c1, complex c2); //(complex &c1, complex &c2)
private:
    double real, image;
};
complex operator+(complex c1, complex c2)            //改成这个出错，为什么(complex &c1, complex &c2)
{

    complex c;
    c.real = c1.real + c2.real;
    c.image = c1.image + c2.image;
    return(c);
}
ostream&operator<<(ostream&output, complex &c2)
{
    return(output << "(" << c2.real << "+" << c2.image << "i)" << endl);
}
int main()
{
    complex c1(5, 4), c2(5, -10), c3;

    c3 = c1 + c2;

    cout << c3 ;
    while (1);

Answer 1

上面的直接直接调用了构造函数了，实际还是类对象相加，下面的因为是引用，不会转换类型