Operator overloading using constructor add two Complex number - c++

Question

I wanted to get a value from the user via using constructor and another value will be in the program itself. I try to code it as below. But constructor is initializing all the values to 0,0(no argument). What to do?
#include<iostream>
using namespace std;
class complex
{
float x;
float y;
public :
complex() //no argument constructor
{
/* cout<<"Enter real = ";
cin>>x;
cout<<"Enter imaginary = ";
cin>>y;*/
}
complex(float real, float imag)
{
cout<<"Enter real = ";
cin>>x;
cout<<"Enter imaginary = ";
cin>>y;
x = real;
y = imag;
}
complex operator+(complex);
void display(void);
};
complex complex :: operator+(complex c)
{
complex temp;
temp.x = x + c.x;
temp.y = y+c.y;
return(temp);
}
void complex :: display(void)
{
cout<<x<<" +i"<<y<<"\n";
}
int main()
{
complex c1,c2(2.5,1.7),c3(0,0);
c3 = c1+c2;
c1.display();
c2.display();
c3.display();
system ("PAUSE");
// return 0;
}

Answer 1

Below is probably what you would want.
I changed your Complex number class to only use one constructor that has default parameters both will default to 0 if you do not provide any parameters.
In your code your parameter less function does nothing and defaults to just using the default constructor for x and y (in the case of floats using 0). You can combine this with the parametered constructor by using default parameters, as mentioned above.
This makes it explicit that if you don't provide values to the Complex constructor you should expect x and y to be 0.
I also added input and output stream operators, but that may not be necessary for your uses.
But it allows you to use cin >> c1; and it is apparent that you expect the user to input the values for c1, instead of embedding that code in the default constructor.
#include<iostream>
using namespace std;
class complex{
float x;
float y;
public :
// it seems like one constructor with default parameters
// should work for your case.
complex(float real = 0, float imag = 0):x(real),y(imag){}
complex operator+(complex);
friend ostream& operator << (ostream& outs, Complex C);
friend istream& operator << (istream& ins, Complex C);
};
ostream& operator << (ostream& outs, Complex C){
cout << C.x << " + i" << C.y;
return outs;
}
istream& operator << (istream& ins, Complex C){
if (ins == cin){
cout << "Enter real part" << endl;
ins >> C.x;
cout << "Enter imaginary part" << endl;
ins >> C.y;
} else {
ins >> C.x >> C.y;
}
return ins;
}
// your plus operator is fine.
int main(){
complex c1,c2(2.5,1.7),c3(0,0); //c1 will have x = 0, y = 0
c3 = c1+c2; // c3.x = 2.5, c3.y = 1.7
cout << c1 << endl; // displays 0 + i0
cout << c2 << endl; // displays 2.5 + i1.7
cout << c3 << endl; // displays 2.5 + i1.7
return 0;
}
Output:
0 + i0
2.5 + i1.7
2.5 + i1.7
If this is not what you expect for output, what would you expect?

Answer 2

I have made a couple of assumptions and modified your code accordingly, the assumptions are:
The second constructor constructs values from the ones present in the main function, so we need a different constructor to create object using the input
c1 contains the values entered by the user and c3 is created using default constructor
Keeping the above in mind the code can be modified as follows:
#include<iostream>
using namespace std;
class complex
{
float x;
float y;
public :
complex() {}
complex(float real, float imag) { x=real; y=imag; } //constructor for creating x and y from values given in the code
complex(istream&);//constructor for creating values entered as input
complex operator+(complex);
void display(void);
};
//definition for constructor for taking user input
complex::complex(istream& in)
{
cout<<"Enter real = ";
in>>x;
cout<<"Enter imaginary = ";
in>>y;
}
complex complex :: operator+(const complex& c) const
{
complex temp;
temp.x = x + c.x;
temp.y = y+c.y;
return(temp);
}
void complex :: display(void)
{
cout<<x<<" +i"<<y<<"\n";
}
int main()
{
complex c1(cin),c2(2.5,1.7),c3;
//note the changes, c1 is made from user input, c2 from constructor and c3 using default constructor
c3 = c1+c2;
c1.display();
c2.display();
c3.display();
}
Make note of the modifications made which I have indicated by the comment lines