Program:

    #include<iostream.h>
    #include<conio.h>

    class complex
    {
    private:
    float real,imag;
    public:
    complex()
    {}
    complex(float r,float I)
    {
    real=r;
    imag=I;
    }
    void add_data(complex c)
    {
    real+=c.real;
    imag+=c.imag;
    }
    complex mul_data(complex c)
    {
    float r=real*c.real-imag*c.imag;
    float I=real*c.imag+imag*c.real;
    return(complex(r,I));
    }
    void complex::display()
    {
    cout<<"\n"<<real<<"+"<<imag<<"i"<<endl;
    }
    };
    void main()
    {
    clrscr();
    complex c3,c1(5,9),c2(11,6);
    c3=c1;
    cout<<"Before any Operation: \n";
    c1.display();
    c2.display();
    c3.display();
    c3=c1.mul_data(c2);
    c1.add_data(c2);
    cout<<"After the Operation: \n";
    c1.display();
    c2.display();
    c3.display();
    getch();
    }