int fsub ( int *a, int *b );

int main ( void )
{
  int sub = 0;
  int a = 1, b = 2;

  sub = fsub ( &a, &b );

  return ( 0 );
}

int fsub ( int *a, int *b )
{
  int sub = 0;

  if ( a > b )              //违背1
  {
    sub = ( *a ) - ( *b );
  }
  else if ( a < b )         //违背2
  {
    sub = ( *b ) - ( *a );
  }
  else
  {
    sub = 0;
  }

  return sub;
}