法一：友元函数

#include<iostream>
#include<cmath>
using namespace std;
class Complex
{
public:
    Complex()
    {
        real=0;
        imag=0;
    }
    Complex(float re,float im)
    {
        real=re;
        imag=im;
    }
Complex(float re)//如果用这种方法，那么complex就不能用引用
{
    real=re;
    imag=0;
}
    friend Complex operator+(const Complex c1,const Complex c2);//只有声明为友元函数，才可以引用两个参数
     friend Complex operator-(const Complex c1,const Complex c2);

    friend ostream &operator<<(ostream &outs,const Complex &B);
    friend istream &operator>>(istream &ins,Complex &C)
    {
        ins>>C.real>>C.imag;
    }
private:
    float real;
    float imag;
    float x;
};


Complex operator+(const Complex c1,const Complex c2)//友元函数的类型是Complex
{
    return Complex(c1.real+c2.real,c1.imag+c2.imag);
}


Complex operator-(const Complex c1,const Complex c2)
{
    return Complex(c1.real-c2.real,c1.imag-c2.imag);
}
ostream &operator<<(ostream&outs,const Complex &B)
{
if(B.imag>0)
    outs<<"("<<B.real<<","<<B.imag<<"i)"<<"\n";
    else
         outs<<"("<<B.real<<","<<B.imag<<"i)"<<"\n";
}

int main( )
{
    Complex c1(5.0,10.0);   	//5+10i
    Complex c2(3.0,-2.5);    	//3-2.5i
    Complex c3,c4;
    c3=c1+c2;
    c4=c1-5;
    cout<<c1<<c2<<c3<<c4;
    Complex c5;
    cout<<"请输入一个复数,实部和虚部以空格分开:"<<endl;
    cin>>c5;
    cout<<"输入的复数为:"<<c5<<endl;
 c4=5+c5;

    cout<<c4<<endl;
    return 0;
}

法二：成员函数

最基础的（最笨的，最麻烦）

#include<iostream>
using namespace std;
class Complex
{public:
    Complex()
    {
        real=0;
        imag=0;
    }
    Complex(float re,float im)
    {
        real=re;
        imag=im;
    }
    //成员函数，负数直接相加减
    Complex operator+(const Complex &c);
    Complex operator-(const Complex &c);
    //浮点数与负数之间的加减,涉及到两个参数，需要用友元函数
    friend Complex operator+(const Complex &c,float hh);
    friend Complex operator+(float hh,const Complex &c);
    friend  Complex operator-(const Complex &c,float hh);
    friend Complex operator-(float hh,const Complex &c);
 friend ostream &operator<<(ostream &outs,const Complex &B);
    friend istream &operator>>(istream &ins,Complex &C)
    {
        ins>>C.real>>C.imag;
    }
protected:
    float real;
    float imag;
};
Complex Complex::operator+(const Complex &c)
{
    return Complex(real+c.real,imag+c.imag);

}
Complex Complex::operator-(const Complex &c)
{
    return Complex(real-c.real,imag-c.imag);

}
 Complex operator+(const Complex &c,float hh)//类型是Complex
 {
     return Complex(c.real+hh,c.imag);
 }
  Complex operator+(float hh,const Complex &c)//类型是Complex
 {
     return Complex(c.real+hh,c.imag);
 }
 Complex operator-(const Complex &c,float hh)//类型是Complex
 {
     return Complex(c.real-hh,c.imag);
 }
  Complex operator-(float hh,const Complex &c)//类型是Complex
 {
     return Complex(hh-c.real,c.imag);
 }
 //输入输出流，只能为友元函数
ostream &operator<<(ostream&outs,const Complex &B)
{
if(B.imag>0)
    outs<<"("<<B.real<<","<<B.imag<<"i)"<<"\n";
    else
         outs<<"("<<B.real<<","<<B.imag<<"i)"<<"\n";
}

 int main( )
{
    Complex c1(5.0,10.0);   	//5+10i
    Complex c2(3.0,-2.5);    	//3-2.5i
    Complex c3,c4;
    c3=c1+c2;
    c4=c1-5;
    cout<<c1<<c2<<c3<<c4;
    Complex c5;
    cout<<"请输入一个复数,实部和虚部以空格分开:"<<endl;
    cin>>c5;
    cout<<"输入的复数为:"<<c5<<endl;
 c4=5+c5;

    cout<<c4<<endl;
    return 0;
}

“我踏碎万家灯火来寻你，山河璀璨权作聘礼”