动态内存分配和堆积损坏

对于学校的作业，我需要创建一个程序，将一个数组插入一个数组，将第一个数组的第一个x值分配到新数组中，然后将所有内容分配给全部第二，然后是其余的第一个。还需要通过动态分配的数组来完成这一点。我不明白为什么，但是由于某种原因，堆正在腐败，我不知道为什么。我刚刚学习指针，所以我发现的解决方案对我来说没有太多意义。

如果有人可以确切地指出我在做错什么，并向我解释一下，以便我可以从错误中学习，我会非常感谢。谢谢！

#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] << ", ";
    }
}