C++ program to create a time class and perform the required operations :

Timeclass.cpp

    #include<iostream>

    using namespace std;

    // Creating a class time...

    class time{
        int hour,minute;

        public:

    // Member functions of class time...

            void initialize(int hr,int mi);
            time sum(time t1,time t2);
            void update(int val);
            void display();
    };

    // Function definitions of the defined functions...

    void time::initialize(int hr,int mi){
        hour=hr;
        minute=mi;
    }

    void time::update(int val){
        minute+=val;
        hour+=(minute/60);
        minute%=60;
        hour%=24;
    }

    time time::sum(time t1,time t2){
        time t3;
        t3.minute=t1.minute+t2.minute;
        t3.hour=t1.hour+t2.hour;
        t3.hour+=(t3.minute/60);
        t3.minute%=60;
        t3.hour%=24;
        return t3;
    }

    void time::display(){
        cout<<hour<<" hours and "<<minute<<" minutes";
    }

    int main()
    {
        int choice;
        int hr,mi;
        time t1,t2,t3;
        int val;
        cout<<"Choice : 1) Update the existing time by a certain value..\n 2) Find the sum of given two times..\n 3) Exit :P";
        while(1){
            cout<<"\nEnter your choice..";
            cin>>choice;
            if(choice==1){
                cout<<"\nEnter the time to be updated in hours and minutes...( hour followed by minute ) ";
                cin>>hr>>mi;
                t1.initialize(hr,mi);
                cout<<"\nEnter the increment value..";
                cin>>val;
                t1.update(val);
                cout<<"\nThe new time  is...";
                t1.display();
                cout<<endl;
            }
            else if(choice==2){
                cout<<"\nEnter the first and second time one by one.. ( hour followed by minute )";
                cin>>hr>>mi;
                t1.initialize(hr,mi);
                cin>>hr>>mi;
                t2.initialize(hr,mi);
                t3=t3.sum(t1,t2);
                cout<<"\nThe sum of the times is.. ";
                t3.display();
                cout<<endl;
            }
            else{
                break;
            }
        }
        return 0;
    }