#define NOT_FOUND -1     /* this is not a legal index, so it is safe. */

int linear_search(int data[], int target, int n)
{
  /* Use parameter n as local counter variable.
   * Initial value is one larger than largest index.
   */
  while ( --n >= 0 )
    if ( data[n] == target )
      break;                 /* found target */

  return n;  /* If while-condition failed, this is NOT_FOUND;
                    * if loop terminated by break, this is the target index.
                    */
}