Resizing dynamic array in c++

arrays, c++

Solution

`A()` is not modifying `nums` to point at the new array. Even if it were, it is deleting the new array, so `nums` would end up pointing at invalid memory. You need to declare the `arr` parameter as a reference, and delete the old array instead of the new array:

void A(int** &arr)
{
    int **resize;
    resize = new int*[size*2];

    for(int i = 0; i < size; i++)
         resize[i] = new int(*arr[i]);

    cout << endl;
    delete[] arr;
    arr = resize;
    size *= 2;
}

For what you are attempting, I think you have too much indirection. Try removing a level:

#include <iostream>
using namespace std;

int *nums;
int size;

void A(int* &arr)
{
    int *resize;
    resize = new int[size*2];

    for(int i = 0; i < size; i++)
        resize[i] = arr[i];

    cout << endl;
    delete[] arr;
    arr = resize;
    size *= 2;
}

int main()
{
    size = 10;
    nums = new int[size];
    for(int i = 0; i < size; i++)
         nums[i] = i;

    for(int i = 0; i < size; i++)
        cout << nums[i] << endl;

    A(nums);

    cout << endl;
    for(int i = (size / 2); i < size; i++)
        nums[i] = i;

    for(int i = 0; i < size; i++)
        cout << nums[i] << endl;

    delete[] nums;
}

Since you are using C++, you should be using a `std::vector` instead of a raw array, then you can eliminate `A()` altogether:

#include <iostream>
#include <vector>
using namespace std;

vector<int> nums;

int main()
{
    nums.resize(10);
    for(int i = 0; i < nums.size(); i++)
         nums[i] = i;

    for(int i = 0; i < nums.size(); i++)
        cout << nums[i] << endl;

    nums.resize(nums.size()*2);

    cout << endl << endl;

    for(int i = (nums.size() / 2); i < nums.size(); i++)
        nums[i] = i;

    for(int i = 0; i < nums.size(); i++)
        cout << nums[i] << endl;
}

Problem

Original source