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