你如何检查输入是否为VB中的负数 [英] How do you check if an input is a negative number in VB

问题描述

我正在尝试进行一些验证，检查文本框中的值是否为整数，然后检查该值是否为负.它正确检查该值是否为整数，但我无法检查该值是否为负数.

I am trying to do some validation which checks if the value in a textbox is an integer then checks if the the value is negative. It correctly checks if the value is an integer but I can't get it to check if the value is negative.

注意:输入的值是参加的比赛次数，因此 comps = 比赛等...

Note: The value being entered is the number of competitions attended so comps = competition etc...

Dim comps As Integer
    Dim value As Double
    If Integer.TryParse(txtCompsEntered.Text, integer) Then
        value = txtCompsEntered.Text
        If value < 0 Then
            lblcompsatten.ForeColor = Color.Red
            txtCompsEntered.ForeColor = Color.Red
            lblcompsatten.Text = "No negative numbers"
        Else
            lblcompsatten.ForeColor = Color.Black
            txtCompsEntered.ForeColor = Color.Black
            lblcompsatten.Text = ""
        End If
        lblcompsatten.ForeColor = Color.Black
        txtCompsEntered.ForeColor = Color.Black
        lblcompsatten.Text = ""
    Else
        lblcompsatten.ForeColor = Color.Red
        txtCompsEntered.ForeColor = Color.Red
        lblcompsatten.Text = "Not a number"
    End If

我已经看过这个帖子，但似乎没有用how-to-check-for-negative-values-in-text-box-in-vb

I have already looked at this thread but it didn't seem to work how-to-check-for-negative-values-in-text-box-in-vb

推荐答案

如果成功，Tryparse 会将输入转换为整数 - 您不需要 comps 和 value 变量.以下是其工作原理的示例:

Tryparse will convert the input to an integer if it succeeds - you don't need both the comps and value variables. Here's an example of how it works:

Dim comps As Integer
Dim input As String = "im not an integer"
Dim input2 As String = "2"

'tryparse fails, doesn't get into comps < 0 comparison
If Integer.TryParse(input, comps) Then
    If comps < 0 Then
        'do something
    End If
Else
   'I'm not an integer!
End If

'tryparse works, goes into comps < 0 comparison
If Integer.TryParse(input2, comps) Then
    If comps < 0 Then
        'do something
    End If
End If

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