Detect the sign in number input - vb.net

Question

how can i detect if the input number in textbox contains "-"
so i can change the output into positive number and
if not contain "-" the output number is become negative
i'm using Vb.net 2010 tnx in advance for who wants to help

Answer 1

Dim output As String
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
If getbyte(TextBox1.Text, 0) = Chr(45) Then ' check whether the first character is - or not
output = New String((From c As Char In TextBox1.Text Select c Where Char.IsDigit(c)).ToArray())
else
output="-" & textbox1.text
End If
msgbox (CInt(output))' will give the number
End Sub
Getbyte function to take each character from a string based on the position
Private Function getbyte(ByVal s As String, ByVal place As Integer) As String
If place < Len(s) Then
place = place + 1
getbyte = Mid(s, place, 1)
Else
getbyte = ""
End If
End Function
if you want to convert the -eve number to positive for calculation you can use

Answer 2

You have couple of options, two of them are:
1) Use StartsWith functions:
If Textbox1.Text.Trim().StartsWith("-"))Then
' It is a negative number
End If
2) If you just need to toggle the number sign, then:
Dim number as Integer = Integer.Parse(Textbox1.Text) ' Preferrably use Integer.TryParse()
number *= -1 ' Toggle the number sign
Using option2, i get:
Dim txta1 As New TextBox
txta1.Text = "-2"
Dim number As Double = Double.Parse(txta1.Text) ' Preferrably use Integer.TryParse()
number *= -1 ' Toggle the number sign
Dim s As String = number & " | "
Output: 2 |