Question

以下代码揭示了我理解中的差距。有人可以告诉我它是什么以及如何修复代码

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim NumberToGuess, Answer As Integer
    NumberToGuess = InputBox("Enter a Secret Number Between 1 and 20!")
    While Answer <> NumberToGuess
        Answer = InputBox("Please enter your guess")
        If IsNumeric(Answer) = False Then MsgBox("That ain't no number")
        If Answer > NumberToGuess Then MsgBox("Too high thicko. Try Again")
        If Answer < NumberToGuess Then MsgBox("Too Low chump. Try Again")
    End While
    MsgBox("Well done you guessed the right number")
End Sub

Answer 1

这个问题有很多问题，你的问题是关于你在谈论哪一个问题。所以我会在这里列出所有这些。

您将NumberToGuess和Answer都声明为整数，并为其指定InputBox的结果。但是InputBox可以返回任何内容（数字或字母）。一旦您尝试将用户的输入分配给NumberToGuess，它就会出错。那是在你检查它是否是数字之前。
如果您有OPTION STRICT ON，它将显示编译错误“Option Strict On禁止从'String'到'Integer'的隐式转换。”保持OPTION STRICT ON是一个不错的选择一般的练习，有助于避免无辜的错误。例如在这里，您要将String类型分配给Integer变量，但不允许这样做。
您使用While循环InputBox。除非他们给出正确答案，否则用户无法取消游戏。 InputBox的“取消”按钮不起作用。
将评估您的所有If条件，而不管之前的条件。我假设您希望一次只显示一个消息框。所以你可能也想使用ElseIf。

要解决问题，请转到：

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim NumberToGuess As String    '<-- declare as string because we will hold the result of InputBox in it.
    Dim Answer As String = ""      '<-- declare as string because we will hold the result of InputBox in it.

    NumberToGuess = InputBox("Enter a Secret Number Between 1 and 20!")
    While Answer <> NumberToGuess
        Answer = InputBox("Please enter your guess")
        If String.IsNullOrEmpty(Answer) Then Exit While '<-- if user pressed cancel button in InputBox.
        If Not IsNumeric(Answer) Then
            MsgBox("That ain't no number")
        ElseIf CInt(Answer) > CInt(NumberToGuess) Then
            MsgBox("Too high thicko. Try Again")
        ElseIf CInt(Answer) < CInt(NumberToGuess) Then
            MsgBox("Too Low chump. Try Again")
        Else
            ' neither less nor more. so this is the correct answer.
            MsgBox("Well done you guessed the right number")
            Exit While
        End If
    End While
End Sub

上面的代码是一个很大的烦恼因为MessageBox，然后是InputBox, then MessageBox , then InputBox ... 要解决此问题，您可以在InputBox本身显示消息。

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim NumberToGuess As String    '<-- declare as string because we will hold the result of InputBox in it.
    Dim Answer As String = ""      '<-- replace with whatever answer you are expecting.
    Dim Message As String = "Please enter your guess"

    NumberToGuess = InputBox("Enter a Secret Number Between 1 and 20!")
    While Answer <> NumberToGuess
        Answer = InputBox(Message)
        If String.IsNullOrEmpty(Answer) Then Exit While '<-- if user pressed cancel button in InputBox.
        If Not IsNumeric(Answer) Then
            Message = "That ain't no number"
        ElseIf CInt(Answer) > CInt(NumberToGuess) Then
            Message = "Too high thicko. Try Again"
        ElseIf CInt(Answer) < CInt(NumberToGuess) Then
            Message = "Too Low chump. Try Again"
        Else
            ' neither less nor more. so this is the correct answer.
            MsgBox("Well done you guessed the right number")
            Exit While
        End If
    End While
End Sub

Answer 2

没什么大不了的 - 你只是错过了一些else;）

private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim NumberToGuess, Answer As Integer
    NumberToGuess = InputBox("Enter a Secret Number Between 1 and 20!")
    While Answer <> NumberToGuess
        Answer = InputBox("Please enter your guess")
        If IsNumeric(Answer) = False Then MsgBox("That ain't no number")
        Else
            If Answer > NumberToGuess Then MsgBox("Too high thicko. Try Again")
            If Answer < NumberToGuess Then MsgBox("Too Low chump. Try Again")
        End If
    End While
    MsgBox("Well done you guessed the right number")

End Sub

问题在于，如果您只是这样写，则检查第一个条件 - 如果您没有输入数字，则会显示消息并检查您的下一个条件 - 您显然只希望检查这些条件是否为一个号码。所以将它包装在Else块

中 BTW：我不认为Answer的缺失值是个问题，但我现在无法检查（我的Linux发行版上的My MonoDevelop与VB.net存在一些问题:( - 调试代码以查找如果是请的话）

Answer 3

问题是InputBox function的返回值它返回一个字符串，并尝试将其分配给整数变量这会强制VB编译器执行从字符串到整数的隐式转换，直到您键入有效数字为止，但是如果您将输入框保留为空，则隐式转换将失败并引发InvalidCastException。

如果使用Option Strict On编译代码，则会在构建期间捕获此代码如果没有它，你的程序会在作业中崩溃 NumberToGuess

的分配中存在同样的问题

Dim NumberToGuess, Answer As Integer
While True
    Dim input = InputBox("Enter a Secret Number Between 1 and 20!")
    if IsNumeric(input) Then
        NumberToGuess = Convert.ToInt32(input)
        Exit While
    Else
        MsgBox("Not a valid number")
    End If
End While    
While Answer <> NumberToGuess
    Dim result = InputBox("Please enter your guess")
    If IsNumeric(result) = False Then 
       MsgBox("That ain't no number")
    Else
       Answer = Convert.ToInt32(result)
       If Answer > NumberToGuess Then MsgBox("Too high thicko. Try Again")
       If Answer < NumberToGuess Then MsgBox("Too Low chump. Try Again")
    End If
End While
MsgBox("Well done you guessed the right number")

我还应该补充一点，Mr Carsten Konig的答案正确指向逻辑代码流中的错误。

Answer 4

您可以使用：

 Dim NumberToGuess, Answer As Integer
        NumberToGuess = InputBox("Enter a Secret Number Between 1 and 20!")
        While Answer <> NumberToGuess
            Answer = InputBox("Please enter your guess")
            If IsNumeric(Answer) = False Then
                MsgBox("That ain't no number")
            Else
                Select Case Answer < NumberToGuess
                    Case True
                        MsgBox("Too Low chump. Try Again")
                    Case False
                        MsgBox("Too high thicko. Try Again")
                    Case Else
                        MsgBox("Well done you guessed the right number")
                End Select
            End If
        End While

我的IF语句和Is Numeric出了什么问题

4 个答案: