Dynamic Memory Allocation and Heap Corruption

Question

For an assignment for school, I need to create a program that takes one array and splices another into it, assigning the first X values of the first array into a new array, then all of the second, and then the rest of the first. It is also required that this is done by means of dynamically allocated arrays. I don't understand why, but for some reason, the heap is becoming corrupted and I can't figure out why. I am just now learning about pointers, so the solutions I have found don't make much sense to me.

If someone could point out exactly what I'm doing wrong, and explain it to me so that I can learn from my mistakes, I'd greatly appreciate it. Thanks!

#include <stdlib.h>
#include <iostream>
#include <time.h>

int* createArray(int);
int* splice(int[], int[], int, int, int);
void arrayPrint(int []);

using namespace std;

int main(void)
{
    int firstLength, secondLength, copyLength;

    cout << "Enter the length of the first array: ";
    cin >> firstLength;
    cout << "Enter the length of the second array: ";
    cin >> secondLength;
    cout << "Enter the length of the first array to be copied: ";
    cin >> copyLength;

    int* firstArray;
    int* secondArray;
    int* thirdArray;

    srand(100);

    firstArray = createArray(firstLength);
    secondArray = createArray(secondLength);

    firstArray = new int[firstLength];
    for (int i = 0; i < firstLength; i++)
        firstArray[i] = rand() % 100;
    secondArray = new int[secondLength];
    for (int i = 0; i < secondLength; i++)
        secondArray[i] = rand() % 100;

    thirdArray = splice(firstArray, secondArray, firstLength, secondLength, copyLength);

    cout << "First Array: " << endl;
    for (int i = 0; i < firstLength; i++)
    {
        cout << firstArray[i] << ", ";
    }
    arrayPrint(firstArray);
    cout << endl << "Second Array: " << endl;
    for (int i = 0; i < secondLength; i++)
    {
        cout << secondArray[i] << ", ";
    }
    arrayPrint(secondArray);
    cout << endl << "Spliced Array: " << endl;
    arrayPrint(thirdArray);

    delete firstArray;
    delete secondArray;
    delete thirdArray;
    system("pause");
    return 0;
}

int* createArray(int arrayLength)
{
    int* createdArray;
    createdArray = new int[arrayLength];
    for (int i = 0; i < arrayLength; i++)
        createdArray[i] = rand();
    return createdArray;
}

int* splice(int firstArray[], int secondArray[], int firstLength, int secondLength, int copyLength)
{
    int* splicedArray;
    splicedArray = new int[copyLength];
    for (int i = 0; i < copyLength; i++)
    {
        splicedArray[i] = firstArray[i];
    }
    for (int j = 0; j < secondLength; j++)
    {
        splicedArray[j + copyLength] = secondArray[j];
    }
    for (int k = 0; k < firstLength - copyLength; k++)
    {
        splicedArray[k + copyLength + secondLength] = firstArray[k + copyLength];
    }
    return splicedArray;
}

void arrayPrint(int toPrint[])
{
    for (int i = 0; i < sizeof(toPrint) / sizeof(*toPrint); i++)
    {
        if ((i % 10) == 9)
            cout << toPrint[i] << endl;
        else
            cout << toPrint[i] << ", ";
    }
}

Answer 1

Combining C_Raj's answer, vinodsaluja's and Wander3r's comments:

you are allocating first and second arrays twice, once is enough, actually more is memory leak (vinodsaluja). Logically, since thirdarray is a combination of first and second arrays, its length should be sum of both array lengths, which is firstlength+secondlength not copylength. This is where heap corruption occurs (vinodsaluja). Finally ararys should be deallocated with delete[] (Wander3r).

C_Raj's code is what the result should be so I'm not copying it.