Chapter 10 Nested If..Then..Else and Case

In a lot of situations, a number of comparisons based on the input must be made. The solution requires the if..then..else structure within other if..then..else statemetns. This is called nesting, and can become very complex very quickly. An alternate method using a Case statement can often simplify these situaltions..

Problem 10

Sample: self extracting 10_nested... self extracting 10_case

Parcel-Post Airfreight charges for parcel delivery based on weight. The following is a table of their charges.

A program is required that will calculate the cost due when the weight is entered. It is necessary to check to see which category the weight falls in. If Weight is not less than 2, it must be checked again to see whether it is less than 5 or greater then 5. The charge, Charge, is calculated based on final rate.

Planning

This is a good opportunity to use the option buttons. If the button is checked (true), then a value for the rate can be assigned.

Also, nested if statements can be used to allow for the three way (or more) selection process.

Pseudocode

If Weight1 Then
  Set Post To 3.50
ElseIf Weight3 Then
      Set Post To 6.50
    Else Set Post To 5.50
End If
Write Post

Code 

Private Sub CalculateCmd_Click()
  Dim Post As Single
 
  If WeightOpt1.checked = True Then
    Post = 3.50
  ElseIf WeightOpt3.checked = True Then
    Post = 6.50
  Else
   Post = 5.50
  End If
  MsgBox "The cost is " & Format(Post, "currency")
End Sub

An alternate solution can be achieved using the CASE statement. The case allows us to compare a given variable against a test value. If the test is true, the program control is passed to the next statement outside the case, otherwise it enacts the associated code. In the case below, there is only a command button procedure that controls the program.

Pseudocode

Get Weight
Case Weight
  Is < 2
    Set Post To 3.50
  From 2 To 5
    Set Post To 5.50
  Is > 5
    Set Post To 6.50
EndCase
Write Post

Note in this version we use a Textbox to get the weight and also display the cost.

Code

Private Sub CalculateCmd_Click()
 Dim weight As Single
        Dim post As decimal ' 2 decimal places for currency
        Dim strweight As String
dim weight as sinlge
        strweight = txtWeight.Text
        weight = Val(strweight)
        Select Case weight
            Case Is < 2
                post = 3.5
            Case 2 To 5
                post = 5.5
            Case Is > 5
                post = 6.5
        End Select
        txtWeight.Text = "Cost is $" & post

End Sub

Exercise 10

1. A CD manufacturing company charges Multimedia companies $6.50 per CD if they create less than 1000 copies. If the company requires more than 10000, they only pay $5.00 a copy. Otherwise, they pay $5.70 a copy. Write a program that will allow the company to calculate how much to charge for different jobs they do. Use the If..then..else statement.
2. Most countries use a sliding scale income tax program based on the amount of money earned. Write a program to calculate the tax owing on an income of an individuals weekly income.

You have been contracted by the Tax Office to write a program that will accept an income and calculate the amount of tax payable. Use the case statement.

Author Mike Leishman

Updated 28 June 1998

edited FDS 28/3/06