Doubling an array?

[Derekrm14]

I'm almost done with this assignment, i just can't figure out how to double the original array, and the unused elements of the second array have to be initialized with 0. I left the last function with a return 0, and that's where i'd like to double the array. Here's my code, Thanks!:

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

void populateArr(int* a, int size);
void printArr(int* a, int size);
int* doubleArray(int* old, int size);
int main()
{
	int* arr, arrX2; //two pointers
	int size; //variable

	cout<< "Enter size of an array: ";
	cin >> size;

	arr = new int[size];

	populateArr(arr, size);
	printArr(arr, size);

	system("pause");
	return 0;
}
void populateArr(int* a, int size)
{
	int* arr = 0;

	for(int i=0;i<size;i++)
	{
		a[i] = rand()%51;
	}
}
void printArr(int a[], int size)
{
	for(int k=0;k<size;k++)
	{
		cout << a[k] << endl;
	}
	cout << "-------------------" << endl;
	cout << "size= " << size << endl;
	cout << "-------------------" << endl;

}
int* doubleArray(int* old, int size)
{
	return 0;
}

[Derekrm14]

bump. can anyone help me out?