try .. except语法如何写?

Question

我现在想
  case strtoint(s1) of
  211: showmessage('heelo');
  220: showmessage('what');
  end;
但s1有可能是字母而不是数字, 所以在转的时候会出错, 如何实现是字母的就不管它转下一个?　也就是说try  .. except语法如何写?

Answer 1

try
  case strtoint(s1) of
  211: showmessage('heelo');
  220: showmessage('what');
  end;
except
  showmessage(程序出错)
end;

Answer 2

case strtointdef(s1, 0) of
  211: showmessage('heelo');
  220: showmessage('what');
    0: ShowMessage('輸入非數字串');
  end;

Answer 3

except
  showmessage(程序出错) //这里写什么让程序不管它继续循环???
end;

Answer 4

case strtointdef(s1, -1) of
  211: showmessage('heelo');
  220: showmessage('what');
  -1：showmessage('number please!');  end;

Answer 5

try
  case strtointdef(s1, 0) of
  211: showmessage('heelo');
  220: showmessage('what');
  0: ShowMessage('輸入非數字串');
  end;
except
  showmessage(程序出错)
end;

Answer 6

try
 case strtoint(s1) of
  211: showmessage('heelo');
  220: showmessage('what');
 end;
except
end;