C++ Trouble adding objects to a list

Question

I am having trouble adding objects to a list.

I want to make a List of Persons, and I know the size of the list is fixed at 5 people. Each Person has an age (int) and a gender (string). I want to add the Persons to the List, but I don't know how, I've only worked with integers now that I think of it.

Below is what I have so far. The random age and gender is working, however clunky that is. I'm thinking instead of creating the Persons as I did, maybe somehow I should create them dynamically in a for loop which will somehow generate the age and gender per loop iteration? Maybe the list should be pointers to the Person objects.

#include <iostream>
#include <list>
#include <memory>

using namespace std;

class Person {
private:
    const int OLDEST_AGE = 100;
    const int YOUNGEST_AGE = 1;
    int age;
    string gender;
public:
    Person()
    {
        age = generateAge();
        gender = generateGender();
    }
    // Person: generate random age for Person, from 1-100
    int generateAge() {
        int randomAge;
        randomAge = rand() % (OLDEST_AGE - YOUNGEST_AGE + 1) + YOUNGEST_AGE;
        return randomAge;
    };
    // Person: generate random gender for Person, Male or Female
    string generateGender() {
        int genderNumber;
        genderNumber = rand() % (1 - 0 + 1) + 0;
        if (genderNumber == 1)
            return "Male";
        else
            return "Female";
    };
    void getStats() {
        cout << "Person Age: " << age << endl;
        cout << "Person Gender: " << gender << endl;
    };
};
int main()
{
    Person P1, P2, P3, P4, P5;
    // Just to see if the objects are created
    P1.getStats();
    P2.getStats();
    P3.getStats();
    P4.getStats();
    P5.getStats();

    list<Person> myList;
    list<Person>::iterator IT;

    for (int i = 1; i <= 5; i++)
        //don't know how to add each Person to the list
        myList.push_back(P1);

    cout << "myList contains: ";
    for (IT = myList.begin(); IT != myList.end(); IT++)
        // similar to above, how do I get the list to print each object's stats
        P1.getStats();
    cout << endl;

    return 0;
}

Hint -- If you had 1000 `Person`'s, would you declare 1000 separate variables named `P1`, `P2`, `P3`, etc. all the way up to `P1000`? Of course not. So what would you do instead? — PaulMcKenzie, Nov 15 '20 at 01:28
Hmm I think I would do a for loop, with int i = 1 and i <= 1000. but in a list myList I would seemingly do myList.push_back(i) with i++, I don't how to do it for a Person. I do see how slow and memory-intensive creating each object would be. — SeePlusPlus, Nov 15 '20 at 01:36
I guess you didn't learn about arrays and containers such as `std::vector` and `std::array`. Why not simply `Person P[5];`? — PaulMcKenzie, Nov 15 '20 at 01:37

score 1 · Answer 1 · answered Nov 15 '20 at 04:21

Using vector would be better in your case if you want to add a lot of elements one after the other as specified in another response to another question comparing list and vector.

Back to the question, as some comments specified, declaring a variable for each person is not a good practice. What you could do instead is to populate your list with a loop like so:

for(int i = 0; i < 5; i++)
    myList.push_back(Person());

Then to access the objects you would just loop through the list again wherever you need to.

for(int i = 0; i < 5; i++)
    myList[i].getStats();

score 0 · Answer 2 · answered Nov 15 '20 at 05:38

You can create a vector, and run through a loop where you instantiate the person, and then push them into the vector. This way, you won't need to create separate person variables like p1, p2, etc., and your vector would hold all the "Person" objects.

vector<Person> people;
for (int i = 0; i < 5; i++) {
    people.push_back(Person());
}

for (Person person : people) {
    person.getStats();
}

C++ Trouble adding objects to a list

2 Answers2