Merge sort - something's WRONG

whatswrong.cpp

#include <stdlib.h>
#include <iostream>

using namespace std;

int * merge_sort(int *A, int begin, int end) {
  if (end - begin <= 1) {
    return A;
  }

  int middle = begin + (end - begin) / 2;
  int *B = merge_sort(A, begin, middle);
  int *C = merge_sort(A, middle, end);

  int *result = (int *) malloc(sizeof(int) * (end - begin));
  int i = begin, j = middle, k = 0;

  for (; i < middle && j < end; ) {
    result[k++] = (C[j] < B[i]) ? C[j++] : B[i++];
  }

  for (; i < (middle - begin); ++i) {
    result[k++] = B[i++];
  }

  for (; j < (end - middle); ++j) {
    result[k++] = C[j++];
  }

  for (i = begin; i < end; ++i) A[i] = result[i - begin];
  free(result);

  return A;
}

int main() {
  int *A, n;
  cin >> n;
  int i;
  for (i = 0; i < n; ++i) {
    cin >> A[i];
  }
  for (i = 0; i < n; ++i) {
    cout << A[i] << ", ";
  }
  cout << endl;
  A = merge_sort(A, 0, n);
  for (i = 0; i < n; ++i) {
    cout << A[i] << ", ";
  }
  cout << endl;
  return 0;
}