Type mismatch VBA error in a variable declared as string

Question

I don't understand the code below, please help.

It keeps on returning a type mismatch error against the variable b.

Dim a As Integer
Dim b As String

a = InputBox("Input the number of items", "Total Number of Items.")
b = InputBox("Which Block?", "Total Number of Items.")

Do While b <> "a" Or "A" Or "B" Or "b"
        MsgBox ("Invalid Block. Try again, Input A or B")
        b = InputBox("Which Block?", "SELECT BLOCK.")
Loop
     If b = "a" Or "A" Then
        Me.ComboBox1.List = Worksheets("Sheet1").Range("a3:a39").Value
    Else
        Me.ComboBox2.List = Worksheets("Sheet2").Range("a3:a35").Value
    End If

Answer 1

You can use Application.InputBox to force a text input for a and and numeric input for b

Using UCASE$ shortens your testing

Dim a As Long
Dim b As String

a = Application.InputBox("Input the number of items", "Total Number of Items.", , , , , , 1)
b = Application.InputBox("Which Block?", "Total Number of Items.", , , , , 2)

Do While UCase$(b) <> "A" And UCase$(b) <> "B"
b = Application.InputBox("Which Block?", "Invalid Entry - Total Number of Items.", , , , , 2)
Loop