关于“为什么不加friend就会提示参数过多”

 1 #include <iostream>
 2 using namespace std;
 3 
 4 class Complex
 5 {
 6     double real, imag;
 7 public:
 8     Complex(double r, double i) :real(r), imag(i){}
 9     Complex operator+(double r);
10      Complex operator+ (double r, const Complex & c);//改为以下即可：friend Complex operator+ (double r, const Complex & c)
11     void ValueGet(){
12         cout << real << "," << imag << endl;
13     }
14 };
15 Complex Complex::operator+(double r)
16 {
17     return Complex(real + r, imag);
18 }
19 
20 int main()
21 {
22     Complex c1(3,2);
23     c1=c1 + 3;
24     c1.ValueGet();
25 }