定义一个复数类Complex，重载运算符“+,-,*,/”,使之能用于复数的加减乘除.....出现的问题及代码

 定义一个复数类Complex，重载运算符“+”、“-”、“*”、“/”，使之能用于复数的加、减、乘、除。要求：将“+”和“-”的运算符重载函数作为Complex的成员函数；将“*”和“/” 的运算符重载函数作为友元函数。编写程序，分别求两个复数之和、差、积、商。
提示：若已知c1=a+bi，c2=c+di，则：
c1+c2=(a+c)+(b+d)i
c1-c2=(a-c)+(b-d)i
c1*c2=(ac-bd)+(ad+bc)i
c1/c2=(ac+bd)/(c*c+d*d)+((bc-ad)/( c*c+d*d))i
运行结果参考如下： 

下面是代码

#include <iostream>
using namespace std;
class Complex
{
public :
Complex (double x=0,double y=0):real(x),imag(y){} 
friend Complex operator * (Complex &c1,Complex &c2);
friend Complex operator / (Complex &c1,Complex &c2);
Complex operator + (Complex &c2 );
Complex operator - (Complex &c2 );
void display();
private :
double real;
double imag;
};
Complex operator * (Complex &c1,Complex &c2)
{
return Complex (c1.real*c2.real-c1.imag*c2.imag,c1.real*c2.imag+c1.imag*c2.real);
}
Complex operator / (Complex &c1,Complex &c2)
{
Complex c;
c.real=(c1.real*c2.real+c1.imag*c2.imag)/(c2.real*c2.real+c2.imag*c2.imag);
c.imag=(c1.imag*c2.real-c1.real*c2.imag)/(c2.real*c2.real+c2.imag*c2.imag);
return c;
}
Complex  Complex ::operator + (Complex &c2)
{
return Complex (real+c2.real,imag+c2.imag);
}
Complex  Complex ::operator - (Complex &c2)
{
return Complex (real-c2.real,imag-c2.imag);
}
void Complex ::display()
{
cout<<"<"<<real<<","<<imag<<"i>"<<endl;
}
int main()
{
Complex c1(3,4),c2(5,-10),c3;
c1.display();
c2.display();
c3=c1+c2;
c3.display();
c3=c1-c2;
c3.display();
c3=c1*c2;
c3.display();
c3=c1/c2;
c3.display();
return 0;

 } 

出现过的问题，

1.

    Complex (double x=0,double y=0):real(x),imag(y){} 

参数初始化表这里需要对x，y赋初值，不然c3在编译时会报错；

2.

    must take either zero or one argument

出现这个问题也困扰了我很久

  二元运算符用成员重载时,   只需要一个参数,   另一个参数由this指针传入 （第一个参数由this指针自动传入到函数中去的.）

Complex operator + (Complex &c1,Complex &c2 );

所以这样写是不对的