c++ vs19 操作符重载 连加连减

Question

问题遇到的现象和发生背景

操作符重载连加连减

问题相关代码，请勿粘贴截图

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <string.h>
#include <string>

using namespace std;//命名空间
class Complex
{
    int a;
    int b;
public:
    Complex(int a, int b) :a(a), b(b)
    {

    }
    friend Complex operator+(Complex& A1, Complex& A2);
    friend Complex operator-(Complex& A1, Complex& A2);
};

Complex operator+(Complex& A1, Complex& A2)//operator+中间不能有空格
{
    Complex temp(A1.a + A2.a, A1.b + A2.b);
    return temp;
}

Complex operator-(Complex& A1, Complex& A2)//返回值不能加引用，返回的是值
{
    Complex temp(A1.a - A2.a, A1.b - A2.b);
    return temp;
}

int main(void)
{
    Complex A1(3, 4);
    Complex A2(4, 5);
    Complex C1 = A1 + A2 + A1;
    Complex C2 = A1 - A2 - A2;
    return 0;
}

###### 运行结果及报错内容 
E0349    no operator "-" matches these operands    
E0349    no operator "+" matches these operands


###### 我的解答思路和尝试过的方法 
如果操作符重载写在类内，连加连减是没有问题的，写成友元函数就出问题了

###### 我想要达到的结果
我想利用操作符重载连加连减

Answer 1

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <string.h>
#include <string>

using namespace std;//命名空间
class Complex
{
    int a;
    int b;
public:
    Complex(int a, int b) :a(a), b(b)
    {

    }
    friend Complex operator+(const Complex& A1, const Complex& A2);//注意着两个参数必须是const Complex&  否则不能连加或者连减，因为a+b+c，会有临时变量，用complex&不能绑定临时变量，必须是const complex&才可以绑定临时变量
    friend Complex operator-(const Complex& A1, const Complex& A2);
};

Complex operator+(const Complex& A1, const Complex& A2)//operator+中间不能有空格
{
    Complex temp(A1.a + A2.a, A1.b + A2.b);
    return temp;
}

Complex operator-(const Complex& A1, const Complex& A2)//返回值不能加引用，返回的是值
{
    Complex temp(A1.a - A2.a, A1.b - A2.b);
    return temp;
}

int main(void)
{
    Complex A1(3, 4);
    Complex A2(4, 5);
    Complex C1 = A1 + A2 + A1;
    Complex C2 = A1 - A2 - A2;
    return 0;
}