Convert input of a textbox to the output of another textbox - vb.net

Question

I'm new to VB, been learning for about three months. I would like to take the input of a textbox, ex. “1234” and turn it into “one, two, three, four” in the second textbox (with commas). No buttons, just two textboxes. This is the code that I've been trying, it doesn't work. I get the error message:
Object reference not set to an instance of an object
If I could get a simple explanation that would be great, anything super complex will just blow my mind and make it more difficult for me to learn. You guys/gals are awesome and I'm ready to learn, thanks.
Dim boxOne = txtNumber.Text.Split(" "c)
Private Sub TxtNumber_TextChanged(sender As Object, e As EventArgs) Handles txtNumber.TextChanged
For Each i As Integer In boxOne
If txtNumber.Text = "1" Then
lblMessage.Text = "one"
End If
If txtNumber.Text = "2" Then
lblMessage.Text = "two"
End If
If txtNumber.Text = "3" Then
lblMessage.Text = "three"
End If
If txtNumber.Text = "4" Then
lblMessage.Text = "four"
End If
If txtNumber.Text = "5" Then
lblMessage.Text = "five"
End If
If txtNumber.Text = "6" Then
lblMessage.Text = "six"
End If
If txtNumber.Text = "7" Then
lblMessage.Text = "seven"
End If
If txtNumber.Text = "8" Then
lblMessage.Text = "eight"
End If
If txtNumber.Text = "9" Then
lblMessage.Text = "nine"
End If
If txtNumber.Text = "10" Then
lblMessage.Text = "ten"
End If
Next
lblMessage.Text = boxOne
End Sub

Answer 1

I suggest to create a mapper, a collection of items that can map/convert one value to another.
A Dictionary comes in handy for this task: given a Key, it returns the associated Value:
Private valueConverter As Dictionary(Of String, String) = New Dictionary(Of String, String) From {
{"0", "Zero"}, {"1", "One"}, {"2", "Two"}, {"3", "Three"}, {"4", "Four"},
{"5", "Five"}, {"6", "Six"}, {"7", "Seven"}, {"8", "Eight"}, {"9", "Nine"}}
A String is a collection of Chars: to parse it, you just need to loop the collection.
If you need to work with the collection of chars directly, you can use the String.ToCharArray() method (e.g., Dim charCollection = [TextBox].Text.ToCharArray()).
Check whether the current char represents a number (Char.IsNumber(char)) and map if it does:
Imports System.Text
Dim sb As New StringBuilder()
For Each part As Char In txtNumber.Text
If Not Char.IsNumber(part) Then Continue For
sb.Append(valueConverter(part) & ", ")
Next
lblMessage.Text = sb.ToString().TrimEnd({","c, " "c})
The StringBuilder class is often used when we need to cancatenate string. Since strings are immutable, each time you add a string to an existing one, you actually generate a new string each time, which needs to be garbage-collected.
For this reason, using a StringBuilder, the code performs way better.

Answer 2

Public Class Form1
Private Sub Str_TextChanged(sender As Object, e As EventArgs) Handles Str.TextChanged
Dim value As String = ""
For Each Str As String In Me.Str.Text
If Str = "1" Then
If value.Length = 0 Then
value = "One"
Else
value = value & ",One"
End If
ElseIf Str = "2" Then
If value.Length = 0 Then
value = "Two"
Else
value = value & ",Two"
End If
ElseIf Str = "3" Then
If value.Length = 0 Then
value = "Three"
Else
value = value & ",Three"
End If
ElseIf Str = "4" Then
If value.Length = 0 Then
value = "Four"
Else
value = value & ",Four"
End If
ElseIf Str = "5" Then
If value.Length = 0 Then
value = "Five"
Else
value = value & ",Five"
End If
ElseIf Str = "6" Then
If value.Length = 0 Then
value = "Six"
Else
value = value & ",Six"
End If
ElseIf Str = "7" Then
If value.Length = 0 Then
value = "Seven"
Else
value = value & ",Seven"
End If
ElseIf Str = "8" Then
If value.Length = 0 Then
value = "Eight"
Else
value = value & ",Eight"
End If
ElseIf Str = "9" Then
If value.Length = 0 Then
value = "Nine"
Else
value = value & ",Nine"
End If
End If
Next
'Your needed value is in variable 'value', use it to set it to another TextBox :)
End Sub
End Class

Answer 3

I don't think we use For Each on integer values to get individual ones. Try using For Each on string.
Here's a code:
Private Sub TxtNumber_TextChanged(sender As Object, e As EventArgs) Handles txtNumber.TextChanged
Dim value As String
For Each Str As String In TxtNumber.Text
If Str = "1" Then
If value.Length = 0 Then
value = "One"
Else
value = value & ",One"
End If
ElseIf Str = "2" Then
If value.Length = 0 Then
value = "Two"
Else
value = value & ",Two"
End If
ElseIf Str = "3" Then
If value.Length = 0 Then
value = "Three"
Else
value = value & ",Three"
End If
ElseIf Str = "4" Then
If value.Length = 0 Then
value = "Four"
Else
value = value & ",Four"
End If
ElseIf Str = "5" Then
If value.Length = 0 Then
value = "Five"
Else
value = value & ",Five"
End If
ElseIf Str = "6" Then
If value.Length = 0 Then
value = "Six"
Else
value = value & ",Six"
End If
ElseIf Str = "7" Then
If value.Length = 0 Then
value = "Seven"
Else
value = value & ",Seven"
End If
ElseIf Str = "8" Then
If value.Length = 0 Then
value = "Eight"
Else
value = value & ",Eight"
End If
ElseIf Str = "9" Then
If value.Length = 0 Then
value = "Nine"
Else
value = value & ",Nine"
End If
End If
Next
'Your needed value is in variable 'value', use it to set it to another TextBox :)
End Sub
And.... its done.