An iterative way of writing merge sort:

#include <iostream>

using namespace std;

void merge(int A[], int l, int r, int e, int B[]) {

	int i = l, j = r, k = l;

	while (i<r && j<e) {

		if (A[i] > A[j]) B[k++] = A[j++];

		else B[k++] = A[i++];

	}

	while (i < r) B[k++] = A[i++];

	while (j < e) B[k++] = A[j++];

}

void mergeSort(int A[], int n) {

	int *B = new int[n];

	for (int w=1; w<n; w<<=1) {

		for (int i=0; i<n; i+=(w<<1)) {

			merge(A, i, min(i+w, n), min(i+(w<<1), n), B);

		}

		for (int i=0; i<n; ++i) A[i] = B[i];

	}

	delete[] B;

}

int main() {

	int A[5] = {5,4,3,2,1};

	mergeSort(A, 5);

	for (int i=0; i<5; ++i) cout<<A[i]<<" ";

	return 0;

}