write cpp code for merging algo with and without use of inbuilt method.

void mergeArrays(int arr1[], int arr2[], int n1,
  int n2, int arr3[]) {
  int i = 0, j = 0, k = 0;
  while (i < n1 && j < n2) {
    if (arr1[i] < arr2[j])
      arr3[k++] = arr1[i++];
    else
      arr3[k++] = arr2[j++];
  }
  while (i < n1)
    arr3[k++] = arr1[i++];
 
  while (j < n2)
    arr3[k++] = arr2[j++];
}