Problem with a VB function on my form (Visual Studio 2019) - vb.net

Question

The function I am trying to create takes in an input from a combo box (Small, Medium, Large)
and then spits out a price based on what was selected. For example, if the user chooses small the calculated price would be 100, if Medium: 200, and if Large: 300. I want the function to be executed after the user clicks the button I created "Calculate Price". I would then have a message box tell the user "The calculated price is: {result}." I currently just keep getting the output "The calculated price is: 0." upon testing my work. Here is the code I am using for the function and button click. (Note: I don't need to have the dollar amounts be returned as integers, they can just be strings Im not too picky about that)
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim result As Integer
result = calcpriceFunction(cboUnitType.ToString)
MessageBox.Show("The calculated price is: " & result)
End Sub
Private Function calcpriceFunction(ByVal untype As String) As Integer
Dim price As String
untype = ""
price = ""
If untype = "Small" Then
Return price = "100"
ElseIf untype = "Medium" Then
Return price = "200"
ElseIf untype = "Large" Then
Return price = "300"
End If
End Function
If anyone can spot a mistake or some sort of convention flaw that would be amazing. I am all out of options right now!

Answer 1

There are many problems with calcpriceFunction
First of all, the code declares that function as returning an integer but instead you try to return a string. This is accepted by the compiler because in the option of your project you have the Option Strict set to Off and this enables automatic type conversion (when possible). While it seems a good thing, in reality this automatic conversion creates lot of problems because you will never know when, for any reason, it doesn't work as expected. So, first thing is to change that option to Option Strict On.
Then it is necessary to remove that untype = "" because it changes the value passed in the parameter.
Finally, don't return at each if/else statement, but just set the price value and use just one final return
Private Function calcpriceFunction(ByVal untype As String) As Integer
' Zero is the default, but I like to be explicit
Dim price As Integer = 0
If untype = "Small" Then
price = 100
ElseIf untype = "Medium" Then
price = 200
ElseIf untype = "Large" Then
price = 300
End If
Return price
End Function
This change will remove the many exit points from your method but also remove another subtle bug present in the original return statement
Return price = "100"
doesn't assign the value "100" to the variable price and then return it, instead it ask the compiler to return the result of the comparison between the current value of price and the constant "100". Or in other words. Is the current value of price equals to "100"? If not return 0

Answer 2

Private Function calculatePrice(untype As String) As Integer
If untype = "Small" Then Return 100
If untype = "Medium" Then Return 200
If untype = "Large" Then Return 300
Throw New ArgumentOutOfRangeException()
End Function
One thing to understand early is that it's very bad to conflate integers and strings. "100" and 100 are not the same value! Moreover, thanks to internationalization/localization and other cultural concerns, converting back and forth between those values is so much slower and error-prone than you can know. It's absolutely something to avoid as much as possible.
Therefore, when accepting numeric input from a user, which of course must start as a string, convert to a numeric type like integer or Decimal as soon as possible, and keep it that way as long as possible, only convert it back to a string again when you must show it to a user again.
The same principle applies to DateTime values.

Answer 3

Here are some modifications to your calcpriceFunction:
Private Function CalculatePrice(untype As String) As Integer
Select Case untype.ToLowerInvariant
Case "small"
Return 100
Case "medium"
Return 200
Case "large"
Return 300
Case Else
Return 0
End Select
End Function
In addition to the issues Steve mentioned in his answer, I suggest you make the function case-insensitive for the untype value. Also, I changed the condition block from If ... ElseIf ... ElseIf ... End If to Select Case for readability. Note that you can return the price directly once you have determined what it is as it is done in this example with Return 100. Finally, I renamed the function to CalculatePrice. There is no reason to abbreviate the name and you should not have Function in a function name.

Answer 4

I made these changes to my Button Click and function and I got my desired outcome! Thank you so much everyone for the help.
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim result As Integer
result = calcpriceFunction(cboUnitType.SelectedValue)
MessageBox.Show("The calculated price is: $" & result & " per month.")
End Sub
Private Function calcpriceFunction(ByVal untype As String) As Integer
Dim price As Integer = 0
If untype = "Small" Then
price = 100
ElseIf untype = "Medium" Then
price = 200
ElseIf untype = "Large" Then
price = 300
End If
Return price
End Function