if, elseif, searching, comparison, greater, smaller - vb.net

Question

I have this code on VB. I get no syntax error but when running and testing the numbers i get "number is not valid" or a wrong answer. Would you please help me what is wrong with this code? Thank you.
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
TextBox2.Text = ""
Dim Num As Integer
Dim str As String
str = TextBox1.Text
Num = Integer.Parse(str)
If Num >= 100 And Num <= 199 Then
TextBox2.Text = "Basement"
ElseIf Num >= 200 And Num <= 500 And Num >= 900 Then
TextBox2.Text = "Main Floor"
ElseIf Num <= 700 And Num >= 501 And Num >= 750 And Num <= 900 Then
TextBox2.Text = "Upper Floor"
ElseIf Num <= 750 And Num >= 700 Then
TextBox2.Text = "Archives"
Else
TextBox2.Text = "Number is not valid"
End If
End Sub

Answer 1

This is impossible
ElseIf Num >= 200 And Num <= 500 And Num >= 900 Then
Here you are asking that a number be greater-equal than 200 (ok), lower-equal than 500 (ok) AND greater-equal than 900 (not ok since you already asked for a number lower-equal than 500). A number can't both be lower than 500 and greater than 900.
Without having the requirements, it's hard to know what your if statement should look like. I would suggest you run through your code manually "on paper" or start with one if statement at a time instead of writing all of them.

Answer 2

I would not mix to many checks in one line as it can get confusing.
Do somthing like this:
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
TextBox2.Text = ""
Dim Num As Integer
Dim str As String
str = TextBox1.Text
Num = Integer.Parse(str)
If Num >= 100 And Num <= 199 Then
TextBox2.Text = "Basement"
ElseIf Num >= 200 And Num <= 500 Then
TextBox2.Text = "Main Floor"
ElseIf Num >= 501 And Num <= 700 then
TextBox2.Text = "Upper Floor"
ElseIf Num ..... and so on
Else
TextBox2.Text = "Number is not valid"
End If
End Sub
Also it's good practice to name your TextBox controls and any other controls:
textbox1 could be something like txtfloornumber
textbox2 could be something like txtfloorname
This makes coming back to your code later in life easier.