Select Case Statements

1
Select Case Statements
2

• Consider the following If statement...
• Dim SomeDay As String
• Dim DayNo As Integer
• SomeDay txtDayName.Text
• If SomeDay "Sun" Then
• DayNo 1
• ElseIf SomeDay "Mon" Then
• DayNo 2
• ElseIf SomeDay "Tue" Then
• DayNo 3
• ElseIf SomeDay "Wed" Then
• DayNo 4
• ElseIf SomeDay "Thu" Then
• DayNo 5
• ElseIf SomeDay "Fri" Then
• DayNo 6
• ElseIf SomeDay "Sat" Then
• DayNo 7

3

• The code reads in a value from a text box called
  txtDayName, and assigns a numeric value to the
  variable DayNo depending on the text entered in
  the box. This numeric value is ultimately
  displayed via a text box caled txtDayNo.
• The above If then ElseIf statement works fine for
  the task at hand, however the problem with these
  kinds of statements is that they can become
  unwieldy as their complexity increases.
• Q. What would we need to do to the above code
  should we need to change the name of the variable
  SameDay?

4
A. We would need to change the following lines of
code.

• Dim SomeDay As String
• SomeDay txtDayName.Text
• If SomeDay "Sun" Then
• ElseIf SomeDay "Mon" Then
• ElseIf SomeDay "Tue" Then
• ElseIf SomeDay "Wed" Then
• ElseIf SomeDay "Thu" Then
• ElseIf SomeDay "Fri" Then
• ElseIf SomeDay "Sat" Then

5
Here is the above code using a Select Case
statement...

• Dim SomeDay As String
• Dim DayNo As Integer
• SomeDay txtDayName.Text
• Select Case SomeDay
• Case "Sun"
• DayNo 1
• Case "Sun"
• DayNo 2
• Case "Sun"
• DayNo 3
• Case "Sun"
• DayNo 4
• Case "Sun"
• DayNo 5
• Case "Sun"
• DayNo 6
• Case "Sun"
• DayNo 7
• Case Else

6

• Notice that the Select Case statement starts with
  the words Select Case along with the name of the
  variable we want to test...
• Select Case SomeDay
• Unlike an If statement we do not insert any
  Boolean expressions at this point.

7

• We then specify the tests (cases) that we require
  using the key word Case, e.g....
• Case "Sun
• DayNo 1
• Case "Sun"
• DayNo 2
• Case "Sun"
• DayNo 3
• Case "Sun"
• DayNo 4
• Case "Sun"
• DayNo 5
• Case "Sun"
• DayNo 6
• Case "Sun"
• DayNo 7
• Case Else
• DayNo 8
• End Select

8

• Q. If we change the name of the variable SomeDay,
  how many changes will be required in the above
  code?
• A. We would need to change....
• Dim SomeDay As String
• SomeDay txtDayName.Text
• Select Case SomeDay
• And that 's it!

9
Sample Application

• In order to see an example of a Select Case
  statement in action, we shall look at the
  creation of the following program....
• The user enters a numeric value between 1 and 7,
  the application outputs the names of a colour of
  the rainbow based on the following values...
• 1 Red
• 2 Orange
• 3 Yellow
• 4 Green
• 5 Blue
• 6 Indigo
• Violet
• Should an invalid number be entered, than an
  error message should be displayed.