如何在 VB.NET 中創建多重 if 語句？

Question

所以我試圖通過將表達式推入堆棧來制作一個中綴來反轉波蘭符號程序。 該程序迭代表達式以查找運算符，一旦找到它，它就會彈出 2 個值並執行計算。 但是，如果我嘗試添加多個 if 語句，則會彈出轉換錯誤。 “if express(i) <> “+” 行用於添加但是如果我要通過添加多個條件來擴展它“if express(i) <> “+” or “-” or “*” 然后它說“從字符串“-”轉換為類型 Boolean 無效。 誰能幫我解決這個問題？ 謝謝。

模塊模塊1

Sub Main()
    Dim expres As String
    Console.WriteLine("Enter infix expression")
    expres = Console.ReadLine()
    Dim S As New Stack
    Dim current(1) As Integer
    Dim temp_val As Integer
    For i = 0 To expres.Length - 1
        If expres(i) <> "+" Then
            S.Push(expres(i))
        End If

        If expres(i) = "+" Then
            current(0) = S.Pop().ToString
            current(1) = S.Pop().ToString
            temp_val = current(0) + current(1)
            Console.WriteLine(temp_val)
            S.Push(temp_val)

        End If
        If expres(i) = "-" Then
            current(0) = S.Pop().ToString
            current(1) = S.Pop().ToString
            temp_val = current(0) - current(1)
            Console.WriteLine(temp_val)
            S.Push(temp_val)

        End If
        If expres(i) = "*" Then
            current(0) = S.Pop().ToString
            current(1) = S.Pop().ToString
            temp_val = current(0) * current(1)
            Console.WriteLine(temp_val)
            S.Push(temp_val)

        End If
        If expres(i) = "/" Then
            current(0) = S.Pop().ToString
            current(1) = S.Pop().ToString
            temp_val = current(0) / current(1)
            Console.WriteLine(temp_val)
            S.Push(temp_val)

        End If
        If expres(i) = "^" Then
            current(0) = S.Pop().ToString
            current(1) = S.Pop().ToString
            temp_val = current(0) ^ current(1)
            Console.WriteLine(temp_val)
            S.Push(temp_val)

        End If
        If expres(i) = "~" Then
            current(0) = S.Pop().ToString
            current(1) = S.Pop().ToString
            temp_val = current(0) + current(1)
            Console.WriteLine(temp_val)
            S.Push(temp_val)

        End If
    Next
    Console.ReadLine()
End Sub

端模塊

Answer 1

每次比較時，您應該 state 左表達式，例如

if express(i) <> "+" or express(i) <> "-" or express(i) <> "*"

Answer 2

試試這個

Module Module1

    Sub Main()
        Dim expres As String
        Console.WriteLine("Enter infix expression")
        expres = Console.ReadLine()
        Dim s As New Stack
        Dim current(1) As Integer
        Dim tempVal As Integer
        For i = 0 To expres.Length - 1

            If Array.IndexOf({"+", "-", "*", "/", "^", "~"}, expres(i)) = -1 Then
                s.Push(expres(i))
            End If

            current(0) = s.Pop().ToString
            current(1) = s.Pop().ToString

            Select Case expres(i)
                Case "+"
                    tempVal = current(0) + current(1)

                Case "-"
                    tempVal = current(0) - current(1)

                Case "*"
                    tempVal = current(0) * current(1)


                Case "/"
                    tempVal = current(0) / current(1)

                Case "^"
                    tempVal = current(0) ^ current(1)


                Case "~"
                    tempVal = current(0) + current(1)

            End Select
            Console.WriteLine(tempVal)
            s.Push(tempVal)

        Next
        Console.ReadLine()
    End Sub
End Module