C++ program to implement a Complex Class and make use of operator overloading:

Complexclass.cpp

#include<iostream>
#include<cmath>

using namespace std;

class cmplx{
    float real,img;

    public:
        cmplx();
        cmplx operator +(cmplx a);
        cmplx operator -(cmplx a);
        void operator =(cmplx a);
        cmplx* operator ->();
        float operator [](int index);
        void operator ()(float a,float b);
        void display();

        friend istream& operator >>(istream &inp,cmplx &a){
            inp>>a.real>>a.img;
            return inp;
        }
        friend ostream& operator <<(ostream &out,cmplx &a){
            if(a.img>=0){
                out<<a.real<<" + "<<a.img<<" i"<<endl;
            }
            else{
               out<<a.real<<" - "<<abs(a.img)<<" i"<<endl;
            }
        }
};

cmplx::cmplx(){
    real=0;
    img=0;
}

cmplx cmplx:: operator +(cmplx a){
    cmplx t;
    t.real=real+a.real;
    t.img=img+a.img;
    return t;
}

cmplx cmplx:: operator -(cmplx a){
    cmplx t;
    t.real=real-a.real;
    t.img=img-a.img;
    return t;
}

float cmplx::operator[](int index){
    if(index==1){
        return real;
    }
    else if(index==2){
        return img;
    }
}

void cmplx::operator ()(float a,float b){
    real=a;
    img=b;
}

void cmplx::operator =(cmplx a){
    real=a.real;
    img=a.img;
}

cmplx* cmplx::operator ->(){
    return this;
}

void cmplx::display(){
    if(img>=0){
        cout<<real<<" + "<<img<<" i"<<endl;
    }
    else{
        cout<<real<<" - "<<abs(img)<<" i"<<endl;
    }
}

int main()
{
    cmplx a,b,c;
    float x,y;
    cout<<"Choice : 1) Addition 2) Subtraction 3) Initialization using function call operator 4) Exit";
    int ch;
    while(1){
        cout<<"\nEnter your choice..";
        cin>>ch;
        if(ch==1){
            cout<<"Enter the real and imaginary part of the first complex number..";
            cin>>a;
            cout<<"Enter the real and imaginary part of the second complex number..";
            cin>>b;
            c=a+b;
            cout<<"The added complex number is ";
            cout<<c;
        }
        else if(ch==2){
            cout<<"Enter the real and imaginary part of the first complex number..";
            cin>>a;
            cout<<"Enter the real and imaginary part of the second complex number..";
            cin>>b;
            c=a-b;
            cout<<"The resultant complex number is ";
            if(c[2]>=0){
                cout<<c[1]<<" + "<<c[2]<<" i";
            }
            else{
                cout<<c[1]<<" - "<<abs(c[2])<<" i";
            }
            cout<<endl;
        }
        else if(ch==3){
            cout<<"Enter the real and imaginary part of the complex number..";
            cin>>x>>y;
            a(x,y);
            b=a;
            b->display();
        }
        else{
            break;
        }
    }
    return 0;
}