merge sort using recursion

#include <iostream>
using namespace std;

void merge(int *, int *, int, int, int); //prototype
void mergesort(int *a, int *b, int low, int high)
{
int pivot;
if (low < high)
{
pivot = (low + high)/2;
mergesort(a, b, low, pivot);
mergesort(a, b, pivot + 1, high);
merge(a, b, low, pivot, high);
}
}
void merge(int *a, int *b, int low, int pivot, int high)
{
int h, i, j, k;
h = low;
i = low;
j = pivot + 1;

while ((h <= pivot) && (j <= high)) // Traverse both halves of the array
{
if (a[h] <= a[j]) // if an element of left half is less than element of right half
{
b[i] = a[h]; // store element of left half in the temporary array
h++; // shift the index of the array from which the element was copied to temporary
}
else // otherwise store the element of the right half in the temporary array
{
b[i] = a[j];
j++; // shift the index of the array from which the element was copied to temporary
}
i++;
}
if (h > pivot) // If traversal of left half is done,
// copy remaining elements from right half to temporary
{
for (k = j; k <= high; k++)
{
b[i] = a[k];
i++;
}
}
else // otherwise copy remaining elements from left half to temporary
{
for (k = h; k <= pivot; k++)
{
b[i] = a[k];
i++;
}
}
for (k = low; k <= high; k++) a[k] = b[k]; // recopy the values from temporary to original array.
}

int main()
{
int a[] = {12, 10, 43, 23, -78, 45, 123, 56, 98, 41, 90, 24};

const int num = sizeof(a)/sizeof(int);

int b[num]; // temporary array to be used for merging

mergesort(a, b, 0, num-1);

for (int i = 0; i < num; i++)
cout << a[i] << " ";
cout << endl;
system("pause");
return 0;
}