C++ Program to implement the Type Conversion in Classes:

TypeConversion.cpp

#include<iostream>

using namespace std;

class duration{
    int mi;

    public:
        duration();
        duration(int t);
        friend istream& operator >>(istream& inp,duration &a){
            inp>>a.mi;
            return inp;
        }
        friend ostream& operator <<(ostream& out,duration &a){
            out<<"Duration is "<<a.mi<<" minutes.";
        }
};

duration::duration(){
    mi=0;
}

duration::duration(int t){
    mi=t;
}

class ttime{
    int hr,mi;

    public:
        ttime();
        ttime(int t);
        ttime(int h,int m);
        operator int();
        operator duration();
        friend istream& operator >>(istream& inp,ttime &a){
            inp>>a.hr>>a.mi;
            return inp;
        }
        friend ostream& operator <<(ostream& out,ttime &a){
            out<<a.hr<<" hours and "<<a.mi<<" minutes. ";
            return out;
        }
};

ttime::ttime(){
    hr=0;
    mi=0;
}

ttime::ttime(int t){
    hr=t/60;
    mi=t%60;
}

ttime::ttime(int h,int m){
    hr=h;
    mi=m;
}

ttime::operator int(){
    return (hr*60+mi);
}

ttime::operator duration(){
    duration d(hr*60+mi);
    return d;
}

int main()
{
    int ch;
    cout<<"Choice : 1) Time to Minutes(primitive type) conversion 2) Minutes(primitive type) to time conversion 3) Time to Duration conversion 4)Exit :P";
    ttime t;
    duration d;
    int n;
    while(1){
        cout<<"\nEnter your choice...";
        cin>>ch;
        if(ch==1){
            cout<<"Enter the time.";
            cin>>t;
            n=t;
            cout<<"The time in minutes is "<<n;
        }
        else if(ch==2){
            cout<<"Enter the time in minutes.";
            cin>>n;
            t=n;
            cout<<t;
        }
        else if(ch==3){
            cout<"Enter the time.";
            cin>>t;
            d=t;
            cout<<d;
        }
        else{
            break;
        }
    }
    return 0;
}