Pointer to array of objects in C++

Question

Write a program to implement pointer to object in a class TRAIN. Train_Number , Train_Name, Arrival_Hr ,Arrival_Min, TimeDiff() are members in class. Member function TimeDiff() is used to find the time difference between Arrival Time (Arrival_Hr and Arrival_Min) and Reached Time ( New given Hr and Min for late arrival) and display the calculated time difference of the specified train. Use pointer to array of objects for different trains.

Is this program the correct answer to the question? I'm asking because I don't know what "Use a pointer to array of objects for different trains" means.

This is the code that I came up with:

#include <iostream>

using namespace std;

class TRAIN{
    public: int Train_Number;
    public: string Train_Name;
    int Arrival_Hr;
    int Arrival_Min;
    TRAIN(int Hr1,int Mn1, int Hr2, int Mn2) {
        Arrival_Hr = Hr2-Hr1;
        Arrival_Min = Mn2-Mn1;
        cout<<Arrival_Hr<<"Hr"<<Arrival_Min<<"min is the difference";
    }
};

int main(){
    TRAIN* ptr[10];
    ptr[0] = new TRAIN(2,30,4,40);
    ptr[1] = new TRAIN(1,20,5,30);
    ptr[0]->Train_Number = 100;
    ptr[0]->Train_Name = "Jansadabti";
    cout<<ptr[0]->Train_Number;
    cout<<ptr[0]->Train_Name;
    return 0;
}

question from:https://stackoverflow.com/questions/65651060/pointer-to-array-of-objects-in-c

Answer 1

The program is a good start, but as-is it does not correctly address the things the question asks for.

You are missing the TimeDiff() method. What you have put into the TRAIN constructor is supposed to be in the TimeDiff() method instead.

The question asks for a “pointer to array of objects”, but you are using an “array of pointers to objects” instead.

Try something more like this:

#include <iostream>
using namespace std;

class TRAIN{
    public:
        int Train_Number;
        string Train_Name;
        int Arrival_Hr;
        int Arrival_Min;

        int TimeDiff(int Reached_Hr, int Reached_Min) const {
            int a_mins = (Arrival_Hr * 60) + Arrival_Min;
            int r_mins = (Reached_Hr * 60) + Reached_Min;
            return r_mins - a_mins;
        }
};

int main() {
    TRAIN* trains = new TRAIN[10];

    trains[0].Train_Number = 100;
    trains[0].Train_Name = "Jansadabti";
    trains[0].Arrival_Hr = 2;
    trains[0].Arrival_Min = 30;

    // populate other trains as needed...

    cout << trains[0].Train_Number << " " << trains[0].Train_Name << ", Time Difference: " << trains[0].TimeDiff(4, 40) << " minute(s)";

    delete[] trains;

    return 0;
}