Dynamic Arrays not properly initializing - c++

Question

I am writing a program that uses two dynamic arrays to sort the original array: One for the left side, and one for the right side.
However, the dynamic arrays do not receive the original array in lines 23 and 28 (As demonstrated by the cout methods throughout the array). They are either empty, or contain elements that are out of bounds. Thus, the program does not work as a whole. My question is then, is the issue with the initialization itself, or is it with the declaration on lines 18-19? I personally believe it is with the declaration, but I am unsure of what I should do with it, as with a Dynamic Array, I do not want to mess with the size too much. I included all of the methods for proper testing, but I will edit this question if they are deemed unnecessary. Thank you in advance for your help.
#include "stdafx.h"
#include <iostream>
using namespace std;
void Merge(int *array, int left, int middle, int right)
{
int * LArray;
int * RArray;
int counter = left;//This counter is used as a marker for the main array.
int mid = middle;
cout<<"Left " << left << "middle: "<< middle << " right: " << right<<endl;
LArray = new int[middle-left + 1];
RArray = new int[right];
/*Initializes LArray*/
for (int i = left; i < middle - left + 1; i++)
{
LArray[i] = array[i];
}
/*Initializes RArray*/
int temp = 0;
for (int i = middle; i < right; i++)
{
RArray[temp] = array[i];
temp++;
}
/*Prints out LArray*/
cout<<"LARRAY: ";
for (int i = left; i < middle- left + 1; i++)
{
cout<<LArray[i]<< " ";
}
/*Prints out RArray*/
cout<<endl<<"RARRY: ";
temp = 0;
for (int i = middle; i < right; i++)
{
temp = 0;
cout<<RArray[temp]<< " ";
temp++;
}
cout<<endl;
while (left <= middle && mid <= right)
{
/*This if statement checks if the number in the left array is smaller than the number in the right array*/
if (LArray[left] < RArray[right])
{
array[counter] = LArray[left];
left++;
counter++;
cout<<"First if: array[counter]: "<< array[counter]<<" LArray[left]" << LArray[left]<<" left: "<< left<<" counter : "<< counter<<endl;
}
/*This else statement checks if the number in the right array is smaller than the number in the left array*/
else
{
array[counter] = RArray[right];
mid++;
counter++;
cout<<" First else: array[counter]: "<< array[counter] << " RArray[right] "<< RArray[right]<<" mid: "<< mid<<" counter : "<< counter<<endl;
}
}
/*If RArray is completed, check this one for any remaining elements.*/
while (left <= middle)
{
array[counter] = LArray[left];
left++;
counter++;
cout<<" First while: array[counter]: "<< array[counter]<<" LArray[left]" << LArray[left]<<" left: "<< left<<" counter : "<< counter<<endl;
}
/*If LArray is completed, check this one for any remaining elements.*/
while (mid <= right)
{
array[counter] = RArray[right];
mid++;
counter++;
cout<<" Second while: array[counter]: "<< array[counter] << " RArray[right] "<< RArray[right]<<" mid: "<< mid<<" counter : "<< counter<<endl;
}
delete [] LArray;
delete [] RArray;
}
void MergeSort( int *array,int left, int right )
{
if ( left < right )
{
int middle = ( left + right ) / 2;
MergeSort( array, left, middle );
MergeSort( array, middle + 1, right );
Merge( array, left, middle, right );
}
};
/*Checks if the array listed is sorted by looping through and checking if the current number is smaller than the previous.*/
bool IsSorted(int* array, unsigned long long size)
{
for (int i = 0; i < size; i++)
{
cout<<array[i]<< " ";
}
cout<<endl;
for (int i = 1; i < size; i++)
{
if (array[i] < array[i-1])
return false;
}
return true;
}
int _tmain(int argc, _TCHAR* argv[])
{
int array[8] = {5, 2, 4, 7, 1, 3, 2, 6};
MergeSort(array, 0, 8);
bool check = IsSorted(array, 8);
if (check)
cout<<"It is sorted!";
else
cout<<"It is not sorted!";
return 0;
}

Answer 1

The idea of merge sort is that you recursively split an array into two halves, sort those two halves and then merge them back together.
Here are the things I see wrong with your code:
Code weirdness that aren't the problem with your algorithm:
Your left array is always larger than necessary, since you're allocating it to have middle elements and initializing it as such.
You initialize right array twice.
The actual problems with your algorithm:
You're not initializing counter correctly, it's always being set as 0 so no matter how deep you are in the callstack, you are always setting elements 0 through middle to be the sorted array instead of the range between left and right.
You're trying to index into the right array with argument right ...which will always be large than the number of elements in right array since you allocated it to have right - middle elements.
You also have an error in your MergeSort function. You are never actually sorting the middle element since in the Merge function array[right] is never added to RArray, so the first recursive call won't sort it, and you're passing in middle + 1 to the second recursive call so it's not sorting it.