C18 Answer

void makeEven( int arr[], int size )
{
  int j;
  for ( j=0; j < size; j++ )
  {
    if ( arr[j]%2 == 1 )
      arr[j] += 1;
    else if ( arr[j]%2 == -1 )
      arr[j] -= 1;
  }
}