kai

看錯了, 忘記用了 exit(1)

[此贴子已经被作者于2006-7-31 7:19:28编辑过]

yeshirow,

I can not go online through my computer, but can go to net through this laptop. So you see, I can just type in english.
What you thought is also mines. But you must think a little more.

The principle is right.
The simplest expression is nothing, then result = 0;
or when the expression is just a number, then result = this number
or when the expression is "a op b" then result = "a op b"

now something more,
an expression can an simple one like mentioned above, it can also be very complate, such like a op b op c op d ...
or (a op b) op c op (d op e) ...

and here op is one of '+', '-', '*', '/'.
when op = '+' then your idea is ok. why? because a + b op c = a + b op c you see the problem is changed to calculate b op c and then a + result from b op c. This is a recussive method.
But you must pay attention, when a * b op c you must first do a * b then the result from a * b work continue with c.
And what is a - b op c op d ? This situation is more complicated.
for example 2 - 3 - 4 + 5 , can you do first 3 - 4 + 5 then 2 - the result from 3 - 4 +5 ? No, you can not do this.
and other example 2 - 3 * 4 - 5 can you do first 3 * 4 - 5 then 2 - the result from 3 * 4 - 5 ? No, you can not do this.
and even -1 + 1 what will you do?

so you see the minus sign is a problem. What I have done is follows:

a - b + c op d = Expression(( Expression(a-b).doCalculation() -> string + c op d).doCalculation()
a - b * c op d = Expression(a - (Expression(b*c).doCalculation() ->string) op d).doCalculation()

ok, I agree with you.
========================================================
say something beside the point:
你不用休息嗎? 一整晚都在論壇裏了.

我很累了, 要大睡一覺.

我在學習 C++ 的路上肯定會遇到很多麻煩, 希望以後能多多指教.

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我在安装 php 呢。 装了几个小时了， 就是不行啊。 按网上的介绍， 在conf 文件里要做很多改动。 我真的不理解了， 发布php 的人怎么不把事情做做好呢？ 这就是开源的一个很大的问题。 我真的实在太生气了。 哇，哇，哇， 气死我了。

那个Apache我印象中好像是有一个高级版本的, 安装完之后连 PHP都装好了,配置好了,不过PHP是4来的

现在都php 5 了。 asp 太霸道相信学的人会越来越少。 在欧洲 php 是主流。 出现这样的局面是因为 firefox 已经可以与IE 抗衡。 甚至超过了IE, 我知道IE7 出来了， 但是我不会去装它。 jsp 太繁琐， 涉及的方方面面太多， 而且 Java 总是给人一种感觉， 那就是它的不确定因素太多， jsp 的学习难度 是3者中最大的。 所以唯一可选的就是 php 了。