In this tutorial, subtraction - operator is overloaded to perform subtraction of a complex number from another complex number. Since - is a binary operator( operator that operates on two operands ), one of the operands should be passed as argument to the operator function and the rest process is similar to the overloading of unary operators.

## Binary Operator Overloading to Subtract Complex Number

```
/* C++ program to demonstrate the overloading of binary operator by subtracting one complex number from another. */
#include <iostream>
using namespace std;
class Complex
{
private:
float real;
float imag;
public:
Complex(): real(0), imag(0){ }
void input()
{
cout<<"Enter real and imaginary parts respectively: ";
cin>>real;
cin>>imag;
}
Complex operator - (Complex c2) /* Operator Function */
{
Complex temp;
temp.real=real-c2.real;
temp.imag=imag-c2.imag;
return temp;
}
void output()
{
if(imag<0)
cout<<"Output Complex number: "<<real<<imag<<"i";
else
cout<<"Output Complex number: "<<real<<"+"<<imag<<"i";
}
};
int main()
{
Complex c1, c2, result;
cout<<"Enter first complex number:\n";
c1.input();
cout<<"Enter second complex number:\n";
c2.input();
/* In case of operator overloading of binary operators in C++ programming, the object on right hand side of operator is always assumed as argument by compiler. */
result=c1-c2; /* c2 is furnised as an argument to the operator function. */
result.output();
return 0;
}
```

In this program, three objects of type Complex is created and user is asked to enter the real and imaginary parts for two complex numbers which is stored in objects c1 and c2. Then statement result=c1-c2 is executed. This statement invokes the operator function Complex operator - (Complex c2). When result=c1-c2 is executed, c2 is passed as argument to the operator function. **In case of operator overloading of binary operators in C++ programming, the object on right hand side of operator is always assumed as argument by compiler.** Then, this function returns the resultant complex number(object) to main() function and then, it is displayed.

Though, this tutorial contains the overloading of - operators, binary operators in C++ programming like: +, *, <, += etc. can be overloaded in similar manner.