VBA - applying function to a sub - vba

Question

im a VBA newbie. I have to create function, that transform state address to state full name eg. CA -> California and apply it to the whole column with addresses.
Given task:
*Open VBE and add module named modFunction. In this module create function (named this function StateFullName) which transform state address into state full name. Function should take one parameter (state address) and return one string value (state full name)
In column 7 each rows with data should have full state name (Tip: use loop and function prepared in modFunction).*
I have created a function, but now I don't know how to apply it in sub with loop.
My function:
Function StateFullName(state_address As String) As String
Select Case state_address
Case "CA": StateFullName = "California"
Case "AZ": StateFullName = "Arizona"
Case "MT": StateFullName = "Montana"
Case "NM": StateFullName = "New Mexico"
End Select
End Function

Answer 1

When setting up your Function as a public function, you can use it in two ways, as a formula and as a Function on other Macros/Subscripts.
Here is a sample of your code:
Public Function statestring(twoletter As String) As String
Select Case twoletter
Case "CA": statestring = "California"
Case "AZ": statestring = "Arizona"
Case Else: statestring = "Unknown State"
End Select
End Function
And here I am using it as a Formula on Column B, top right you can see the formula:
And here I am using it on another Sub as a Function to fill Column C:
(It could be a lot better coded but I just wrote it as it came to mind)
Edit: After a quick thought an offset would be make it much better
Sub getFullState()
Set wk = ThisWorkbook
With wk.Sheets("Sheet1")
'startRow = 2 ' Removed
For Each Rng In .Range("A2:A4")
'Next line Replaced with Offset
'.Range("C" & startRow).Value = statestring(Rng.Value)
Rng.Offset(0, 2).Value = statestring(Rng.Value)
'startRow = startRow + 1 'Removed
Next
End With
End Sub