CODEWITHSUNDEEP
c++classobjectdynamic-memory-allocationdynamic-arrays
eM3e
eM3e

Reputation: 55

Changing Dynamic Arrays lengths?

Lets say that I own a repair shop and I want to add a vehicle to my database each time a new customer comes to my shop. Assuming that I have a car class that asks for all the necessary information. Is is possible to create a dynamic array of this object that is constantly adding or subtracting the amount of customer cars that come into the shop, or is this more improbable?

Ex.

    using namespace std; //I know its not a good idea to use, prof wants us too.

    class Car{
         Car(){
         //get user data
         }
    };

    int main () {

          int choice;
          static int counter = 0;
          Car *car = new Car[Counter];

          cout << "Would you like to add a vehicle to the our database(yes/no): ";
          cin >> choice;
                if (choice == "yes") {
                    car[counter].Car::Car();
                    counter++;
                }

Upvotes: 0

Views: 58

Answers (3)

aaamourao
aaamourao

Reputation: 128

You may be looking for vector from the Standard Template Library:

#include <vector>

...
vector<Car> car;
...
if (choice == "yes") {
    car.push_back(Car{});
}

You won't need counter variable on your main function, since you can use the method size, which returns the number of elements inside the vector.

e.g.

car.size();

For removing items, use the method pop_back or the method erase

e.g.

car.pop_back();  // Remove last element from car vector
car.erase(3); // Remove the 4th element from car vector

Upvotes: 1

Arnav Borborah
Arnav Borborah

Reputation: 11769

Yes, this is possible with raw dynamic arrays, but it is very complicated as you are going to have to manually manage your memory and deal with a lot of pointer arithmetic. To simplify this process, the STL contains std::vector which represents an dynamic array that can easily be changed in size. For example:

std::vector<Car> car;

cout << "Would you like to add a vehicle to the our database(yes/no): ";
cin >> choice;

if (choice == "yes") {
    car.push_back(Car{}); // No indices required; Just add a new car to the end
    counter++; // You might not even need this, 
               // as there is std::vector::size for that
}

Similarly, to remove a Car, you can use std::vector::pop_back which can be called in the same way as std::vector::push_back.

Upvotes: 1

Stephan Lechner
Stephan Lechner

Reputation: 35154

Letting a dynamically allocated array grow and shrink is possible, but tricky. Fortunately, standard library provides containers (e.g. std::vector) for exactly this issue:

struct Car{
    Car(string _type) : type(_type) { };
    string type;
};

int main () {

    std::vector<Car> cars;
    while(1) {
        string input;
        cout << "Enter the type of a new car (or 'exit'):" << endl;
        if (!(cin >> input) || input=="exit") {
            break;
        }
        cout << "added." << endl;
        cars.emplace_back(input);
    }

    cout << "you have entered " << cars.size() << " car(s):" << endl;
    for(auto car : cars) {
        cout << car.type << endl;
    }

}

Upvotes: 1

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