Iterative mergesort in C++ - c++

Question

i'm currently working on iterative version of mergesort, but i've encountered a problem. The program crashes when there are specific sizes of array's like 34,35,36 or 100(just few examples) and it works for the rest(fe works for powers of 2). I've ran some tests and debugged it, and the problem seems to be with the ranges of my iterations/left,right halves of mergesort, but i can't find it. I'll be thankful for your help.
Code:
int * loadArray(int size){ //i input size of array and it assigns random numbers
int *array = new int[size];
srand( time( NULL ) );
for( int i = 0; i < size; i++ )
array[i]=rand()%100;
return array;
}
void merge(int arr[], int left, int middle, int right)
{
int i, j, k; //iterators
int n1 = middle-left + 1; //indexes
int n2 = right-middle; //indexes
int Left[n1], Right[n2]; //arrays holding halves
for (i = 0; i < n1; i++)
Left[i] = arr[left + i];//assigning values to left half
for (j = 0; j < n2; j++)
Right[j] = arr[middle + 1+ j];//assigning values to right half
i = 0;
j = 0;
k = left;
while (i < n1 && j < n2) //comparing and merging
{
if (Left[i] <= Right[j])
{
arr[k] = Left[i];
i++;
}
else
{
arr[k] = Right[j];
j++;
}
k++;
}
while (i < n1) //leftovers
{
arr[k] = Left[i];
i++;
k++;
}
while (j < n2) //leftovers
{
arr[k] = Right[j];
j++;
k++;
}
}
void mergeSortIter(int array[], int size) //the function which is being called and handles division of the array
{
double startTime = clock(); //start measuring time
int i;
int left_start;
for (i=1; i<=size-1; i = 2*i)
{
for (left_start=0; left_start<size-1; left_start += 2*i)
{
int mid = left_start + i - 1;
int right_end = min(left_start + 2*i - 1, size-1);
merge(array, left_start, mid, right_end);
}
//showArray(array,size);
}
cout << double( clock() - startTime ) / (double)CLOCKS_PER_SEC<< " seconds." << endl; //output the time measured
}