解析字符串用VB等式 [英] parsing string to equation with vb

问题描述

有没有一种方法来分析运营商在字符串等式中使用？

Is there a way to parse operators in String to use in an equation?

例：5 + 4

在这种情况下，5个和4都是字符串，但我可以通过使用for循环把它解析为整数，对不对？但怎么样+操作？

In this case, the 5 and 4 are strings, but I can parse them to integer by using a for loop, right? But what about the + operator?

好吧，我用ChrisF的解决方案

Okay I used ChrisF's solution

推荐答案

海报似乎已经解决了他的问题，但以防万一有人发现这个职位找我做了一个非常简单的解决答案。

The poster seems to have solved his problem, but just in case someone finds this post looking for an answer I have made a very simple solution.

        Dim s As String = "5 * 4" 'our equation
        s = s.Replace(" ", "") 'remove spaces
        Dim iTemp As Double = 0 'double (in case decimal) for our calculations
        For i As Integer = 0 To s.Length - 1 'standard loop
            If IsNumeric(s(i)) Then
                iTemp = Convert.ToInt32(s(i)) - 48 'offset by 48 since it gets ascii value when converted
            Else
                Select Case s(i)
                    Case "+"
                        'note s(i+1) looks 1 index ahead
                        iTemp = iTemp + (Convert.ToInt32(s(i + 1)) - 48)'solution
                    Case "-"
                        iTemp = iTemp - (Convert.ToInt32(s(i + 1)) - 48)'solution
                    Case "*"
                        iTemp = iTemp * (Convert.ToInt32(s(i + 1)) - 48)'solution
                    Case "/"
                        'you should check for zero since x/0 = undefined
                        iTemp = iTemp / (Convert.ToInt32(s(i + 1)) - 48)'solution
                End Select
                Exit For 'exit since we are done
            End If
        Next
        MsgBox(iTemp.ToString)

这仅仅是一个简单快速和肮脏的解决方案。我在学校（许多很久以前）学到的方法是做这些类型的堆栈与问题。复杂的数学字符串可以使用堆栈进行解析。

This is just a simple quick and dirty solution. The way I learned in school (many many moons ago) was to do these types of problems with stacks. Complex mathematical strings can be parsed using stacks.

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