VBA custom function to compare values - vba

Question

I am trying to create a custom function that basically does this:
The function is in column F and looks at column C to see what the valus is in there.
If it is USA_USD it will display USD in colomn F
If it is Australia_AUD the it will display AUD in colomn F
etc.
Function The_Decider(DealCurrency, X)
If DealCurrency = "USA_USD" Then X = "USD"
Else
If DealCurrency = "Australia_AUD" Then X = "AUD"
Else
If DealCurrency = "Switzerland_CHF" Then X = "CHF"
Else
If DealCurrency = "China_CNY" Then X = "CNY"
Else
If DealCurrency = "EMU_EUR" Then X = "EUR"
Else
If DealCurrency = "Great Britain_GBP" Then X = "GBP"
Else
If DealCurrency = "Hong Kong_HKD" Then X = "HKD"
Else
If DealCurrency = "Japan_JPY" Then X = "JPY"
Else
If DealCurrency = "Korea(South)_KRW" Then X = "KRW"
Else
If DealCurrency = "Viet Nam_VND" Then X = "VND"
End Function
Why I am getting #value in column C?

Answer 1

First of all, you don't actually supply a return value at any point. Also you would probably be better going for a Select Case block for the sake of readability.
You should declare the return type in the function header, then use the same name as the function to return the value in your code:
Function The_Decider(ByVal DealCurrency As String) As String '// <~~ return type
Dim X As String
Select Case DealCurrency
Case "USA_USD": X = "USD"
Case "Australia_AUD": X = "AUD"
Case "Switzerland_CHF": X = "CHF"
Case "China_CNY": X = "CNY"
Case "EMU_EUR": X = "EUR"
Case "Great Britain_GBP": X = "GBP"
Case "Hong Kong_HKD": X = "HKD"
Case "Japan_JPY": X = "JPY"
Case "Korea(South)_KRW": X = "KRW"
Case "Viet Nam_VND": X = "VND"
Case Else: X = "Unknown"
End Select
The_Decider = X '// <~~ the part that actually returns the value
End Function
Although seeing as your input appears to have the currency code in the last 3 letters, I wouldn't even use a UDF. Simply using a worksheet formula would suffice:
=RIGHT(C1,3)