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Managing Conditional Statements

 
 
 

Fundamentals of Managing Conditional Statements

 

Conditional Nesting

We know how to create normal conditional statements and loops. Here is an example:

Module Exercise

    Private Sub RequestNumber()
        Dim Number%

        Number% = InputBox("Enter a number that is lower than 5")

        If Number% <= 5 Then
            MsgBox(Number%)
        End If

    End Sub

    Public Function Main() As Integer
        RequestNumber()
        Return 0
    End Function

End Module

When this program runs, if the user enter a number lower than 5 (included), a message box would display that number. If the user enter a number higher than 5, the program would end but would not display it. In a typical program, after validating a condition, you may want to take action. To do that, you can create a section of program inside the validating conditional statement. In fact, you can create a conditional statement inside of another conditional statement. This is referred to as nesting a condition. Any condition can be nested in another and multiple conditions can be included inside of another.

Here is an example where an If...Then condition is nested inside of a Do...Loop While loop:

Module Exercise

    Private Sub RequestNumber()
        Dim Number%

        Do
            Number% = InputBox("Enter a number that is lower than 5")

            If Number% <= 5 Then
                MsgBox(Number%)
            End If
        Loop While Number <= 5
    End Sub

    Public Function Main() As Integer
        RequestNumber()
        Return 0
    End Function

End Module

When the program runs, it asks the user to provide a number lower than 5 (included). If the user provides such a number, the value of the number is displayed and the user is asked to provide another number. This would continue as long as the user is entering a number lower than 5. Otherwise, the program would stop.

Practical LearningPractical Learning: Nesting Conditions

  1. Start Microsoft Visual Basic and create a Console Application named BCR7 (or open the BCR6 application from the previous lesson and go to the next section)
  2. In the Solution Explorer, right-click Module1.vb and click Rename
  3. Type BethesdaCarRental.vb and press Enter
  4. Change the document as follows:
    Module BethesdaCarRental
        Private Function GetEmployeeName(ByVal EmplNbr As Long) As String
            Dim Name As String
    
            If EmplNbr = 22804 Then
                Name = "Helene Mukoko"
            ElseIf EmplNbr = 92746 Then
                Name = "Raymond Kouma"
            ElseIf EmplNbr = 54080 Then
                Name = "Henry Larson"
            ElseIf EmplNbr = 86285 Then
                Name = "Gertrude Monay"
            Else
                Name = "Unknown"
            End If
    
            Return Name
        End Function
    
        Public Function Main() As Integer
            Dim EmployeeNumber As Long, EmployeeName As String
            Dim CustomerName As String
            Dim TagNumber As String, CarSelected As String
            Dim RentStartDate As Date, RentEndDate As Date
            Dim NumberOfDays As Integer
            Dim RateType As String, RateApplied As Double
            Dim OrderTotal As Double
            Dim OrderInvoice As String
            Dim Answer As MsgBoxResult
    
            RateType = "Weekly Rate"
            RateApplied = 0
            OrderTotal = RateApplied
    
            Do
                EmployeeNumber =
    		CLng(InputBox("Employee number (who processed this order):",
                                               "Bethesda Car Rental", "00000"))
    
                EmployeeName = GetEmployeeName(EmployeeNumber)
    
                CustomerName = InputBox("Enter Customer Name:",
                                               "Bethesda Car Rental", "John Doe")
    
                TagNumber = InputBox("Enter the tag number of the car to rent:",
                                               "Bethesda Car Rental", "000000")
    
                CarSelected = Microsoft.VisualBasic.Switch(
                            TagNumber = "297419", "BMW 335i",
                            TagNumber = "485M270", "Chevrolet Avalanche",
                            TagNumber = "247597", "Honda Accord LX",
                            TagNumber = "924095", "Mazda Miata",
                            TagNumber = "772475", "Chevrolet Aveo",
                            TagNumber = "M931429", "Ford E150XL",
                            TagNumber = "240759", "Buick Lacrosse",
                            True, "Unidentified Car")
    
                RentStartDate = CDate(InputBox("Enter Rent Start Date:",
                                               "Bethesda Car Rental", #1/1/1900#))
                RentEndDate = CDate(InputBox("Enter Rend End Date:",
                                               "Bethesda Car Rental", #1/1/1900#))
                NumberOfDays = DateDiff(DateInterval.Day, RentStartDate, RentEndDate)
    
                RateApplied = CDbl(InputBox("Enter Rate Applied:", _
                                               "Bethesda Car Rental", 0))
    
                Dim TemporaryRate As Double
    
                Select Case NumberOfDays
                    Case 0, 1
                        RateType = "Daily Rate"
                        OrderTotal = RateApplied
                    Case 2
                        RateType = "Weekend Rate"
                        TemporaryRate = RateApplied * 50 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * 2
                    Case 2 To 7
                        RateType = "Weekly Rate"
                        TemporaryRate = RateApplied * 25 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * NumberOfDays
                    Case Is > 8
                        RateType = "Monthly Rate"
                        TemporaryRate = RateApplied * 15 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * NumberOfDays
                End Select
    
                OrderInvoice = "===========================" & vbCrLf &
                          "=//= BETHESDA CAR RENTAL =//=" & vbCrLf &
                          "==-=-= Order Processing =-=-==" & vbCrLf &
                      "------------------------------------------------" & vbCrLf &
                          "Processed by:" & vbTab & EmployeeName & vbCrLf &
                          "Processed for:" & vbTab & CustomerName & vbCrLf &
                      "------------------------------------------------" & vbCrLf &
                          "Car Selected:" & vbCrLf &
                          vbTab & "Tag #:" & vbTab & TagNumber & vbCrLf &
                          vbTab & "Car:" & vbTab & CarSelected & vbCrLf &
                      "------------------------------------------------" & vbCrLf &
                          "Start Date:" & vbTab & RentStartDate & vbCrLf &
                          "End Date:" & vbTab & RentEndDate & vbCrLf &
                          "Nbr of Days:" & vbTab & NumberOfDays & vbCrLf &
                    "------------------------------------------------" & vbCrLf &
                          "Rate Type:" & vbTab & RateType & vbCrLf &
                  "Rate Applied:" & vbTab & FormatCurrency(RateApplied) & vbCrLf &
                    "Order Total:" & vbTab & FormatCurrency(OrderTotal) & vbCrLf &
                          "==========================="
    
                MsgBox(OrderInvoice,
                          MsgBoxStyle.Information Or MsgBoxStyle.OkOnly,
                       "Bethesda Car Rental")
    
                Answer = MsgBox("Do you want to process another order?",
                                MsgBoxStyle.Information Or MsgBoxStyle.YesNo,
                                "Bethesda Car Rental")
            Loop Until Answer = MsgBoxResult.No
            Return 0
        End Function
    
    End Module
  5. Execute the application
  6. Enter the employee number as 92746, the customer name as James Wiley, the tag number as 297419, the car condition as 1, the tank level as 5, the start date as 10/22/2008, the end date as 11/07/2008, and the rate applied 49.95
     
    Bethesda Car Rental
  7. When asked whether you want to process another order, click No
  8. Close the message box and the DOS window to return to your programming environment

The Goto Statement

The Goto statement allows a program execution to jump to another section of a procedure in which it is being used. In order to use the Goto statement, insert a name on a particular section of your procedure so you can refer to that name. The name, also called a label, is made of one word and follows the rules we have applied to names (the name can be anything), then followed by a colon ":".

The following program uses a For loop to count from 2 to 18, but when it encounters 10, it jumps to a designated section of the program:

Module Exercise

    Public Function Main() As Integer
        Dim i As Integer

        For i = 2 To 18 Step 1
            If i = 10 Then
                GoTo StoppingHere
            End If
            MsgBox("Value: " & i)
        Next

StoppingHere:
        MsgBox("The execution jumped here.")
        Return 0
    End Function

End Module

This would produce:

In the same way, you can create as many labels as you judge them necessary in your code and refer to them when you want. Here is an example with various labels:

Module Exercise

    Public Function Main() As Integer
        Dim Answer As Byte

        Answer = InputBox(" -=- Multiple Choice Question -=-" & vbCrLf &
                          "To create a constant in your code, " &
                          "you can use the Constant keyword" & vbCrLf &
                          "Your choice (1=True/2=False)? ")


        If Answer = 1 Then GoTo Wrong
        If Answer = 2 Then GoTo Right

Wrong:  MsgBox("Wrong: The keyword used to create a constant is Const")
        GoTo Leaving

Right:  MsgBox("Right: Constant is not a keyword")

Leaving:
        Return 0
    End Function

End Module

Here is an example of executing the program with Answer = 1:

Go To

Go To

Here is another example of executing the same program with Answer = 2:

Go To

Go To

 

Practical LearningPractical Learning: Going To a Label

  1. To go to a label, change the document as follows:
    Module BethesdaCarRental
        Private Function GetEmployeeName(ByVal EmplNbr As Long) As String
            Dim Name As String
    
            If EmplNbr = 22804 Then
                Name = "Helene Mukoko"
            ElseIf EmplNbr = 92746 Then
                Name = "Raymond Kouma"
            ElseIf EmplNbr = 54080 Then
                Name = "Henry Larson"
            ElseIf EmplNbr = 86285 Then
                Name = "Gertrude Monay"
            Else
                Name = "Unknown"
            End If
    
            Return Name
        End Function
    
        Public Function Main() As Integer
            Dim EmployeeNumber As Long, EmployeeName As String
            Dim CustomerName As String
            Dim TagNumber As String, CarSelected As String
            Dim RentStartDate As Date, RentEndDate As Date
            Dim NumberOfDays As Integer
            Dim RateType As String, RateApplied As Double
            Dim OrderTotal As Double
            Dim OrderInvoice As String
            Dim Answer As MsgBoxResult
    
            RateType = "Weekly Rate"
            RateApplied = 0
            OrderTotal = RateApplied
    
            Do
                EmployeeNumber =
    		CLng(InputBox("Employee number (who processed this order):", _
                                               "Bethesda Car Rental", "00000"))
    
                EmployeeName = GetEmployeeName(EmployeeNumber)
    
                CustomerName = InputBox("Enter Customer Name:",
                                               "Bethesda Car Rental", "John Doe")
    
                TagNumber = InputBox("Enter the tag number of the car to rent:", _
                                               "Bethesda Car Rental", "000000")
    
                CarSelected = Microsoft.VisualBasic.Switch(
                            TagNumber = "297419", "BMW 335i",
                            TagNumber = "485M270", "Chevrolet Avalanche",
                            TagNumber = "247597", "Honda Accord LX",
                            TagNumber = "924095", "Mazda Miata",
                            TagNumber = "772475", "Chevrolet Aveo",
                            TagNumber = "M931429", "Ford E150XL",
                            TagNumber = "240759", "Buick Lacrosse",
                            True, "Unidentified Car")
    
                RentStartDate = CDate(InputBox("Enter Rent Start Date:",
                                               "Bethesda Car Rental", #1/1/1900#))
                RentEndDate = CDate(InputBox("Enter Rend End Date:",
                                               "Bethesda Car Rental", #1/1/1900#))
    
                If RentEndDate < RentStartDate Then
                    MsgBox("The values you entered for the start and end dates " &
                           "are not consecute. The rent start date must occur " &
                           "prior to the rent end date",
                           MsgBoxStyle.Critical Or MsgBoxStyle.OkOnly,
                           "Bethesda Car Rental")
                    GoTo RestartOrderProcessing
                End If
    
                NumberOfDays = DateDiff(DateInterval.Day, RentStartDate, RentEndDate)
    
                RateApplied = CDbl(InputBox("Enter Rate Applied:",
                                               "Bethesda Car Rental", 0))
    
                Dim TemporaryRate As Double
    
                Select Case NumberOfDays
                    Case 0, 1
                        RateType = "Daily Rate"
                        OrderTotal = RateApplied
                    Case 2
                        RateType = "Weekend Rate"
                        TemporaryRate = RateApplied * 50 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * 2
                    Case 2 To 7
                        RateType = "Weekly Rate"
                        TemporaryRate = RateApplied * 25 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * NumberOfDays
                    Case Is > 8
                        RateType = "Monthly Rate"
                        TemporaryRate = RateApplied * 15 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * NumberOfDays
                End Select
    
                OrderInvoice = "===========================" & vbCrLf &
                          "=//= BETHESDA CAR RENTAL =//=" & vbCrLf &
                          "==-=-= Order Processing =-=-==" & vbCrLf &
                      "------------------------------------------------" & vbCrLf &
                          "Processed by:" & vbTab & EmployeeName & vbCrLf &
                      "Processed for:" & vbTab & CustomerName & vbCrLf &
                      "------------------------------------------------" & vbCrLf &
                          "Car Selected:" & vbCrLf &
                          vbTab & "Tag #:" & vbTab & TagNumber & vbCrLf &
                          vbTab & "Car:" & vbTab & CarSelected & vbCrLf &
                      "------------------------------------------------" & vbCrLf &
                          "Start Date:" & vbTab & RentStartDate & vbCrLf &
                          "End Date:" & vbTab & RentEndDate & vbCrLf &
                          "Nbr of Days:" & vbTab & NumberOfDays & vbCrLf &
                      "------------------------------------------------" & vbCrLf &
                          "Rate Type:" & vbTab & RateType & vbCrLf &
                    "Rate Applied:" & vbTab & FormatCurrency(RateApplied) & vbCrLf &
                      "Order Total:" & vbTab & FormatCurrency(OrderTotal) & vbCrLf &
                          "==========================="
    
                MsgBox(OrderInvoice,
                          MsgBoxStyle.Information Or MsgBoxStyle.OkOnly,
                       "Bethesda Car Rental")
    
    RestartOrderProcessing:
                Answer = MsgBox("Do you want to process another order?",
                                MsgBoxStyle.Information Or MsgBoxStyle.YesNo,
                                "Bethesda Car Rental")
            Loop Until Answer = MsgBoxResult.No
            Return 0
        End Function
    
    End Module
  2. Execute the application
  3. Enter the employee number as 92746, the customer name as James Wiley, the tag number as 297419, the car condition as 1, the tank level as 5, the start date as 10/22/2008, the end date as 11/07/2008, and the rate applied 49.95
  4. When asked whether you want to process another order, click Yes
  5. Enter the employee number as 92746, the customer name as James Wiley, the tag number as 297419, the car condition as 1, the tank level as 5, the start date as 11/07/2008, the end date as 11/10/2008, and the rate applied 49.95
  6. When asked whether you want to process another order, click No
  7. Close the message box and the DOS window to return to your programming environment

Negating a Conditional Statement

So far, we have learned to write a conditional statement that is true or false. You can reverse the true (or false) value of a condition by making it false (or true). To support this operation, the Visual Basic language provides an operator called Not. Its formula is:

Not Expression

When writing the statement, type Not followed by a logical expression. The expression can be a simple Boolean expression. Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim IsMarried As Boolean

        MsgBox("Is Married: " & IsMarried)
        MsgBox("Is Married: " & Not IsMarried)

        Return 0
    End Function

End Module

This would produce:

Not

Not

In this case, the Not operator is used to change the logical value of the variable. When a Boolean variable has been "notted", its logical value has changed. If the logical value was True, it would be changed to False and vice versa. Therefore, you can inverse the logical value of a Boolean variable by "notting" or not "notting" it.

Now consider the following program we saw in Lesson 11:

Module Exercise

    Public Function Main() As Integer
        Dim IsMarried As Boolean
        Dim TaxRate As Double

        TaxRate = 33.0

        MsgBox("Tax Rate: " & TaxRate & "%")

        IsMarried = True
        If IsMarried = True Then
            TaxRate = 30.65

            MsgBox("Tax Rate: " & TaxRate & "%")
        End If

        Return 0
    End Function

End Module

This would produce:

If Condition If Condition

Probably the most classic way of using the Not operator consists of reversing a logical expression. To do this, you precede the logical expression with the Not operator. Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim IsMarried As Boolean
        Dim TaxRate As Double

        TaxRate = 33.0

        MsgBox("Tax Rate: " & TaxRate & "%")

        IsMarried = True
        If Not IsMarried Then
            TaxRate = 30.65

            MsgBox("Tax Rate: " & TaxRate & "%")
        End If

        Return 0
    End Function

End Module

This would produce:

If Condition

In the same way, you can negate any logical expression.

Exiting a Procedure or a Loop

 

Exiting a Procedure

In the conditional statements and loops we have created so far, we assumed that the whole condition would be processed. Here is an example:

Module Exercise

    Private Sub ShowNumbers()
        Dim Number As Short

        For Number = 1 To 6
            MsgBox(Number)
        Next

    End Sub

    Public Function Main() As Integer
        ShowNumbers()
        Return 0
    End Function

End Module

This would produce:

Exiting Exiting Exiting
Exiting Exiting Exiting

In some cases, you may want to exit a conditional statement or a loop before its end. To assist with with this, the Visual Basic language provides the Exit keyword. This keyword works like an operator. It can be applied to a procedure or a For loop. Consider the following ShowNames procedure:

Module Exercise

    Private Sub ShowNames()
        MsgBox("Patricia Katts")
        MsgBox("Gertrude Monay")
        MsgBox("Hermine Nkolo")
        MsgBox("Paul Bertrand Yamaguchi")
    End Sub

    Public Function Main() As Integer
        ShowNames()
        Return 0
    End Function

End Module

When the procedure is called, it displays four message boxes that each shows a name. Imagine that at some point you want to ask the compiler to stop in the middle of a procedure. To do this, in the section where you want to stop the flow of a procedure, type Exit Sub. Here is an example:

Module Exercise

    Private Sub ShowNames()
        MsgBox("Patricia Katts")
        MsgBox("Gertrude Monay")
        Exit Sub
        MsgBox("Hermine Nkolo")
        MsgBox("Paul Bertrand Yamaguchi")
    End Sub

    Public Function Main() As Integer
        ShowNames()
        Return 0
    End Function

End Module

This time, when the program runs, the ShowNames procedure would be accessed and would start displaying the message boxes. After displaying two, the Exit Sub would ask the compiler to stop and get out of the procedure.

Because a function is just a type of procedure that is meant to return a value, you can use the Exit keyword to get out of a function before the End Function line. To do this, in the section where you want to stop the flow of the function, type Exit Function.

Exiting a For Loop Counter

You can also exit a For loop. To do this, in the section where you want to stop, type Exit For. Here is an example to stop a continuing For loop:

Module Exercise

    Private Sub ShowNumbers()
        Dim Number As Short

        For Number = 1 To 6
            MsgBox(Number)
            If Number = 4 Then
                Exit For
            End If
        Next

    End Sub

    Public Function Main() As Integer
        ShowNumbers()
        Return 0
    End Function

End Module

When this program executes, it is supposed to display numbers from 1 to 6, but an If...Then condition states that if it gets to the point where the number is 4, it should stop. If you use an Exit For statement, the compiler would stop the flow of For and continue with code after the Next keyword.

Exiting a Do Loop

You can also use the Exit operator to get out of a Do loop. To do this, inside of a Do loop where you want to stop, type Exit Do.

Logical Conjunction

 

Introduction

As mentioned already, you can nest one conditional statement inside of another. To illustrate, imagine you create a program that would be used by a real estate company that sells houses. You may face a customer who wants to purchase a single family house but the house should not cost over $550,001. To implement this scenario, you can first write a program that asks the user to select a type of house and then a conditional statement would check the type of house. Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim Type As String
        Dim Choice As Integer
        Dim Value As Double
        
        Type = "Unknown"

        Choice = CInt(InputBox("Enter the type of house you want to purchase"
		  & vbCrLf &
                  "1. Single Family" & vbCrLf &
                  "2. Townhouse" & vbCrLf &
                  "3. Condominium" & vbCrLf & vbCrLf &
                  "You Choice? "))
        Value = CDbl(InputBox("Up to how much can you afford?"))

        Type = Choose(Choice, "Single Family",
                              "Townhouse",
                              "Condominium")

        Return 0
    End Function

End Module

If the user selects a single family, you can then write code inside the conditional statement of the single family. Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim Type As String
        Dim Choice As Integer
        Dim Value As Double
        
        Type = "Unknown"

        Choice = CInt(InputBox("Enter the type of house you want to purchase"
		  & vbCrLf &
                  "1. Single Family" & vbCrLf &
                  "2. Townhouse" & vbCrLf &
                  "3. Condominium" & vbCrLf & vbCrLf &
                  "You Choice? "))
        Value = CDbl(InputBox("Up to how much can you afford?"))

        Type = Choose(Choice, "Single Family",
                              "Townhouse",
                              "Condominium")

        If Choice = 1 Then
            MsgBox("Desired House Type:      " & vbTab & Type & vbCrLf &
                   "Maximum value afforded:  " & vbTab & FormatCurrency(Value))
        End If

        Return 0
    End Function

End Module

In that section, you can then write code that would request and check the value the user entered. If that value is valid, you can take necessary action. Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim Type As String
        Dim Choice As Integer
        Dim Value As Double
        
        Type = "Unknown"

        Choice =
	  CInt(InputBox("Enter the type of house you want to purchase" & vbCrLf &
                  "1. Single Family" & vbCrLf &
                  "2. Townhouse" & vbCrLf &
                  "3. Condominium" & vbCrLf & vbCrLf &
                  "You Choice? "))
        Value = CDbl(InputBox("Up to how much can you afford?"))

        Type = Choose(Choice, "Single Family",
                              "Townhouse",
                              "Condominium")

        If Choice = 1 Then
            MsgBox("Desired House Type:      " & vbTab & Type & vbCrLf &
                   "Maximum value afforded:  " & vbTab & FormatCurrency(Value))
            If Value <= 550000 Then
                MsgBox("Desired House Matched")
            Else
                MsgBox("The House Doesn't Match the Desired Criteria")
            End If
        End If

        Return 0
    End Function

End Module

A Conditional Conjunction

Using conditional nesting, we have seen how you can write one conditional that depends on another. But you must write one first condition, check it, then nest the other condition. This works fine and there is nothing against it. To provide with with an alternative, you can use what is referred to as a logical conjunction. It consists of writing one If...Then expression that checks two conditions at the same time. To illustrate, once again consider a customer who wants to purchase a single family home that is less than $550,000. You can consider two statements as follows:

  1. The house is single family
  2. The house costs less than $550,000

To implement it, you would need to write an If...Then condition as:

If The house is single family AND The house costs less than $550,000 Then

    Validate

End If

In the Visual Basic language, the operator used to perform a logical conjunction is And. Here is an example of using it:

Module Exercise

    Public Function Main() As Integer
        Dim Type As String
        Dim Choice As Integer
        Dim Value As Double

        Type = "Unknown"

        Choice = _
	  CInt(InputBox("Enter the type of house you want to purchase" & vbCrLf &
                  "1. Single Family" & vbCrLf &
                  "2. Townhouse" & vbCrLf &
                  "3. Condominium" & vbCrLf & vbCrLf &
                  "You Choice? "))
        Value = CDbl(InputBox("Up to how much can you afford?"))

        Type = Choose(Choice, "Single Family",
                              "Townhouse",
                              "Condominium")

        If Type = "Single Family" And Value <= 550000 Then
            MsgBox("Desired House Type:      " & vbTab & Type & vbCrLf &
                   "Maximum value afforded:  " & vbTab & FormatCurrency(Value))
            MsgBox("Desired House Matched")
        Else
            MsgBox("The House Doesn't Match the Desired Criteria")
        End If

        Return 0
    End Function

End Module

By definition, a logical conjunction combines two conditions. To make the program easier to read, each side of the conditions can be included in parentheses. Here is an example:

Module Exercise

    Public Function Main() As Integer
        . . . No Change

        If (Type = "Single Family") And (Value <= 550000) Then
            MsgBox("Desired House Type:      " & vbTab & Type & vbCrLf &
                   "Maximum value afforded:  " & vbTab & FormatCurrency(Value))
            MsgBox("Desired House Matched")
        Else
            MsgBox("The House Doesn't Match the Desired Criteria")
        End If

        Return 0
    End Function

End Module

 

To understand how logical conjunction works, from a list of real estate properties, after selecting the house type, if you find a house that is a single family home, you put it in the list of considered properties:

Type of House House
The house is single family True
  

If

If you find a house that is less than or equal to $550,000, you retain it:

Price Range Value
$550,000 True

For the current customer, you want a house to meet BOTH criteria. If the house is a town house, based on the request of our customer, its conditional value is false. If the house is less than $550,000, such as $485,000, the value of the Boolean Value is true:

If

If

AND

If the house is a town house, based on the request of our customer, its conditional value is false. If the house is more than $550,000, the value of the Boolean Value is true. In logical conjunction, if one of the conditions is false, the result if false also. This can be illustrated as follows:

Type of House House Value Result
Town House $625,000 Town House AND $625,000
False False False

Suppose we find a single family home. The first condition is true for our customer. With the AND Boolean operator, if the first condition is true, then we consider the second criterion. Suppose that the house we are considering costs $750,500: the price is out of the customer's range. Therefore, the second condition is false. In the AND Boolean algebra, if the second condition is false, even if the first is true, the whole condition is false. This would produce the following table:

Type of House House Value Result
Single Family $750,500 Single Family AND $750,500
True False False

Suppose we find a townhouse that costs $420,000. Although the second condition is true, the first is false. In Boolean algebra, an AND operation is false if either condition is false:

Type of House House Value Result
Town House $420,000 Town House AND $420,000
False True False

If we find a single family home that costs $345,000, both conditions are true. In Boolean algebra, an AND operation is true if BOTH conditions are true. This can be illustrated as follows:

Type of House House Value Result
Single Family $345,000 Single Family AND $345,000
True True True

These four tables can be resumed as follows:

If Condition1 is If Condition2 is Condition1
AND
Condition2
False False False
False True False
True False False
True True True

As you can see, a logical conjunction is true only of BOTH conditions are true.

Practical LearningPractical Learning: Using a Logical Conjunction

  1. Start Microsoft Visual Basic and create a Console Application named BCR7 (or open the BCR6 application from the previous lesson and go to the next section)
  2. In the Solution Explorer, right-click Module1.vb and click Rename
  3. Type BethesdaCarRental.vb and press Enter
  4. Change the document as follows:
    Module BethesdaCarRental
        Private Function GetEmployeeName(ByVal EmplNbr As Long) As String
            Dim Name As String
    
            If EmplNbr = 22804 Then
                Name = "Helene Mukoko"
            ElseIf EmplNbr = 92746 Then
                Name = "Raymond Kouma"
            ElseIf EmplNbr = 54080 Then
                Name = "Henry Larson"
            ElseIf EmplNbr = 86285 Then
                Name = "Gertrude Monay"
            Else
                Name = "Unknown"
            End If
    
            Return Name
        End Function
    
        Private Function GetCarCondition() As String
            Dim Status As Integer
            Dim Condition As String
    
            Do
                Status = CInt(InputBox( _
    		"After inpecting it, enter car condition:" & vbCrLf &
                    "1. Excellent - No scratch, no damage, no concern" & vbCrLf &
                    "2. Good - Some concerns (scratches or missing something)." &
                    "Make sure the customer is aware." & vbCrLf &
                    "3. Drivable - The car is good enough to drive." &
                    "The customer must know the status of the car " &
                    "and agree to rent it",
                    "Bethesda Car Rental", 1))
    
                Select Case Status
                    Case 1
                        Condition = "Excellent"
                    Case 2
                        Condition = "Good"
                    Case 3
                        Condition = "Drivable"
                    Case Else
                        Condition = "Unknown"
                End Select
    
            Loop Until (Status > 0) And (Status < 4)
    
            Return Condition
        End Function
    
        Public Function Main() As Integer
            Dim EmployeeNumber As Long, EmployeeName As String
            Dim CustomerName As String
            Dim TagNumber As String, CarSelected As String
            Dim CarCondition As String
            Dim RentStartDate As Date, RentEndDate As Date
            Dim NumberOfDays As Integer
            Dim RateType As String, RateApplied As Double
            Dim OrderTotal As Double
            Dim OrderInvoice As String
            Dim Answer As MsgBoxResult
    
            RateType = "Weekly Rate"
            RateApplied = 0
            OrderTotal = RateApplied
    
            Do
                EmployeeNumber =
    		CLng(InputBox("Employee number (who processed this order):",
                                               "Bethesda Car Rental", "00000"))
    
                EmployeeName = GetEmployeeName(EmployeeNumber)
    
                CustomerName = InputBox("Enter Customer Name:",
                                               "Bethesda Car Rental", "John Doe")
    
                TagNumber = InputBox("Enter the tag number of the car to rent:",
                                               "Bethesda Car Rental", "000000")
    
                CarSelected = Microsoft.VisualBasic.Switch(
                            TagNumber = "297419", "BMW 335i",
                            TagNumber = "485M270", "Chevrolet Avalanche",
                            TagNumber = "247597", "Honda Accord LX",
                            TagNumber = "924095", "Mazda Miata",
                            TagNumber = "772475", "Chevrolet Aveo",
                            TagNumber = "M931429", "Ford E150XL",
                            TagNumber = "240759", "Buick Lacrosse",
                            True, "Unidentified Car")
    
                CarCondition = GetCarCondition()
    
                RentStartDate = CDate(InputBox("Enter Rent Start Date:",
                                               "Bethesda Car Rental", #1/1/1900#))
                RentEndDate = CDate(InputBox("Enter Rend End Date:",
                                               "Bethesda Car Rental", #1/1/1900#))
    
                If RentEndDate < RentStartDate Then
                    MsgBox("The values you entered for the start and end dates " &
                           "are not consecute. The rent start date must occur " &
                           "prior to the rent end date",
                           MsgBoxStyle.Critical Or MsgBoxStyle.OkOnly,
                           "Bethesda Car Rental")
                    GoTo RestartOrderProcessing
                End If
                NumberOfDays = DateDiff(DateInterval.Day, RentStartDate, RentEndDate)
    
                RateApplied = CDbl(InputBox("Enter Rate Applied:",
                                               "Bethesda Car Rental", 0))
    
                Dim TemporaryRate As Double
    
                Select Case NumberOfDays
                    Case 0, 1
                        RateType = "Daily Rate"
                        OrderTotal = RateApplied
                    Case 2
                        RateType = "Weekend Rate"
                        TemporaryRate = RateApplied * 50 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * 2
                    Case 2 To 7
                        RateType = "Weekly Rate"
                        TemporaryRate = RateApplied * 25 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * NumberOfDays
                    Case Is > 8
                        RateType = "Monthly Rate"
                        TemporaryRate = RateApplied * 15 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * NumberOfDays
                End Select
    
                OrderInvoice = "===========================" & vbCrLf &
                          "=//= BETHESDA CAR RENTAL =//=" & vbCrLf &
                          "==-=-= Order Processing =-=-==" & vbCrLf &
                  "------------------------------------------------" & vbCrLf &
                          "Processed by:" & vbTab & EmployeeName & vbCrLf &
                          "Processed for:" & vbTab & CustomerName & vbCrLf &
                  "------------------------------------------------" & vbCrLf &
                          "Car Selected:" & vbCrLf &
                          vbTab & "Tag #:" & vbTab & TagNumber & vbCrLf &
                          vbTab & "Car:" & vbTab & CarSelected & vbCrLf &
                          "Car Condition:" & vbTab & CarCondition & vbCrLf &
                  "------------------------------------------------" & vbCrLf &
                          "Start Date:" & vbTab & RentStartDate & vbCrLf &
                          "End Date:" & vbTab & RentEndDate & vbCrLf &
                          "Nbr of Days:" & vbTab & NumberOfDays & vbCrLf &
                  "------------------------------------------------" & vbCrLf &
                          "Rate Type:" & vbTab & RateType & vbCrLf &
                  "Rate Applied:" & vbTab & FormatCurrency(RateApplied) & vbCrLf &
                  "Order Total:" & vbTab & FormatCurrency(OrderTotal) & vbCrLf &
                          "==========================="
    
                MsgBox(OrderInvoice, _
                          MsgBoxStyle.Information Or MsgBoxStyle.OkOnly,
                       "Bethesda Car Rental")
    
    RestartOrderProcessing:
                Answer = MsgBox("Do you want to process another order?",
                                MsgBoxStyle.Information Or MsgBoxStyle.YesNo,
                                "Bethesda Car Rental")
            Loop Until Answer = MsgBoxResult.No
            Return 0
        End Function
    
    End Module
  5. Execute the application
  6. Enter the employee number as 92746, the customer name as James Wiley, the tag number as 297419, and the car condition as -5 and click OK
     
  7. Enter the car condition as 8tank level as 5 and press Enter
  8. Enter the car condition as 2, the start date as 11/07/2008, the end date as 11/10/2008, and the rate applied 49.95
  9. When asked whether you want to process another order, click Yes
  10. Enter the employee number as 54080, the customer name as Sunil Ajat, the tag number as 240759, the car condition as 3, the tank level as 3, the start date as 11/05/2008, the end date as 11/15/2008, and the rate applied 70.25
  11. When asked whether you want to process another order, click No
  12. Close the message box and the DOS window to return to your programming environment

Combining Conjunctions

As seen above, the logical conjunction operator is used to combine two conditions. In some cases, you will need to combine more than two conditions. Imagine a customer wants to purchase a single family house that costs up to $450,000 with an indoor garage. This means that the house must fulfill these three requirements:

  1. The house is a single family home
  2. The house costs less than $450,001
  3. The house has an indoor garage

Here the program that could be used to check these conditions:

Module Exercise

    Public Function Main() As Integer
        Dim Type As String
        Dim Choice As Integer
        Dim Value As Double
        Dim IndoorGarageAnswer As MsgBoxResult
        Dim Answer As String

        Type = "Unknown"

        Choice =
	  CInt(InputBox("Enter the type of house you want to purchase" & vbCrLf &
                  "1. Single Family" & vbCrLf &
                  "2. Townhouse" & vbCrLf &
                  "3. Condominium" & vbCrLf & vbCrLf &
                  "You Choice? "))
        Value = CDbl(InputBox("Up to how much can you afford?"))

        Type = Choose(Choice, "Single Family",
                              "Townhouse",
                              "Condominium")

        IndoorGarageAnswer =
	  MsgBox("Does the house have an indoor garage (1=Yes/0=No)? ",
                                    MsgBoxStyle.Question Or MsgBoxStyle.YesNo,
                                    "Real Estate")
        Answer = IIf(IndoorGarageAnswer = MsgBoxResult.Yes, "Yes", "No")

        If (Type = "Single Family") And (Value <= 550000) And
	   (IndoorGarageAnswer = MsgBoxResult.Yes) Then
            MsgBox("Desired House Type:      " & vbTab & Type & vbCrLf &
                   "Maximum value afforded:  " & vbTab &
		   FormatCurrency(Value) & vbCrLf &
                "House has indoor garage: " & vbTab & Answer)
            MsgBox("Desired House Matched")
        Else
            MsgBox("The House Doesn't Match the Desired Criteria")
        End If

            Return 0
    End Function

End Module

We saw that when two conditions are combined, the compiler first checks the first condition, followed by the second. In the same way, if three conditions need to be considered, the compiler evaluates the truthfulness of the first condition:

Type of House
A
Town House
False

If the first condition (or any condition) is false, the whole condition is false, regardless of the outcome of the other(s). If the first condition is true, then the second condition is evaluated for its truthfulness:

Type of House Property Value
A B
Single Family $655,000
True False

If the second condition is false, the whole combination is considered false:

A B A && B
True False False

When evaluating three conditions, if either the first or the second is false, since the whole condition would become false, there is no reason to evaluate the third. If both the first and the second conditions are false, there is also no reason to evaluate the third condition. Only if the first two conditions are true will the third condition be evaluated whether it is true:

Type of House Property Value Indoor Garage
A B C
Single Family $425,650 None
True True False

The combination of these conditions in a logical conjunction can be written as A && B && C. If the third condition is false, the whole combination is considered false:

A B A && B C A && B && C
True True True False False

From our discussion so far, the truth table of the combinations can be illustrated as follows:

A B C A && B && C
False Don't Care Don't Care False
True False Don't Care False
True True False False

The whole combination is true only if all three conditions are true. This can be illustrated as follows:

A B C A && B && C
False False False False
False False True False
True False False False
True False True False
False True False False
False True True False
True True False False
True True True True
 
 
 
 

Logical Disjunction: OR

 

Introduction

Our real estate company has single family homes, townhouses, and condominiums. All of the condos have only one level, also referred to as a story. Some of the single family homes have one story, some have two and some others have three levels. All townhouses have three levels.

Another customer wants to buy a home. The customer says that he primarily wants a condo, but if our real estate company doesn't have a condominium, that is, if the company has only houses, whatever it is, whether a house or a condo, it must have only one level (story) (due to an illness, the customer would not climb the stairs). When considering the properties of our company, we would proceed with these statements:

  1. The property is a condominium
  2. The property has one story

If we find a condo, since all of our condos have only one level, the criterion set by the customer is true. Even if we were considering another (type of) property, it wouldn't matter. This can be resumed in the following table:

Type of House House
Condominium True

The other properties would not be considered, especially if they have more than one story:

Number of Stories Value
3 False

We can show this operation as follows:

Condominium One Story Condominium or 1 Story
True False True

Creating a Logical Disjunction

To support "either or" conditions in the Visual Basic language, you use the Or operator. Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim Type As String
        Dim Choice As Integer
        Dim Stories As Short
        
        Type = "Unknown"

        Choice =
	  CInt(InputBox("Enter the type of house you want to purchase" & vbCrLf &
                  "1. Single Family" & vbCrLf &
                  "2. Townhouse" & vbCrLf &
                  "3. Condominium" & vbCrLf & vbCrLf &
                  "You Choice? ", "Real Estate", 1))

        Type = Choose(Choice, "Single Family",
                              "Townhouse",
                              "Condominium")
        Stories = CShort(InputBox("How many stories?", "Real Estate", 1))

        If Choice = 1 Or Stories = 1 Then
            MsgBox("Desired House Type:" & vbTab & Type & vbCrLf &
                   "Number of Stories:" & vbTab & vbTab & Stories)
            MsgBox("Desired House Matched")
        Else
            MsgBox("The House Doesn't Match the Desired Criteria")
        End If

        Return 0
    End Function

End Module

As done for the And operator, to make a logical disjunction easy to read, you can include each statement in parentheses:

Module Exercise

    Public Function Main() As Integer
        . . . No Change

        If (Choice = 1) Or (Stories = 1) Then
            MsgBox("Desired House Type:" & vbTab & Type & vbCrLf &
                   "Number of Stories:" & vbTab & vbTab & Stories)
            MsgBox("Desired House Matched")
        Else
            MsgBox("The House Doesn't Match the Desired Criteria")
        End If

        Return 0
    End Function

End Module

Here is an example of running the program:

Or

Or

Suppose that, among the properties our real estate company has available, there is no condominium. In this case, we would then consider the other properties:

Type of House House
Single Family False

If we have a few single family homes, we would look for one that has only one story. Once we find one, our second criterion becomes true:

Type of House One Story Condominium OR 1 Story
False True True

This can be illustrated in the following run of the above program:

Or

Or

Or

If we find a condo and it is one story, both criteria are true. This can be illustrated in the following table:

Type of House One Story Condominium OR 1 Story
False True True
True True True

The following run of the program demonstrates this:

Or

Or

Or

A Boolean OR operation produces a false result only if BOTH conditions ARE FALSE:

If Condition1 is If Condition2 is Condition1 OR Condition2
False True True
True False True
True True True
False False False

Here is another example of running the program:

Or

Or

 

Practical LearningPractical Learning: Using Logical Disjunctions

  1. Start Microsoft Visual Basic and create a Console Application named BCR7 (or open the BCR6 application from the previous lesson and go to the next section)
  2. In the Solution Explorer, right-click Module1.vb and click Rename
  3. Type BethesdaCarRental.vb and press Enter
  4. Change the document as follows:
    Module BethesdaCarRental
        Private Function GetEmployeeName() As String
            Dim Name As String
            Dim EmployeeNumber As Long
    
            EmployeeNumber =
    	    CLng(InputBox("Employee number (who processed this order):",
                                           "Bethesda Car Rental", "00000"))
    
            If EmployeeNumber = 22804 Then
                Name = "Helene Mukoko"
            ElseIf EmployeeNumber = 92746 Then
                Name = "Raymond Kouma"
            ElseIf EmployeeNumber = 54080 Then
                Name = "Henry Larson"
            ElseIf EmployeeNumber = 86285 Then
                Name = "Gertrude Monay"
            Else
                Name = "Unknown"
            End If
    
            Return Name
        End Function
    
        Private Function GetCarCondition() As String
            Dim Status As Integer
            Dim Condition As String
    
            Do
                Status =
    	CInt(InputBox("After inpecting it, enter car condition:" & vbCrLf &
                      "1. Excellent - No scratch, no damage, no concern" & vbCrLf &
                      "2. Good - Some concerns (scratches or missing something)." &
                      "Make sure the customer is aware." & vbCrLf &
                      "3. Drivable - The car is good enough to drive." &
                      "The customer must know the status of the car " &
                                          "and agree to rent it",
                                          "Bethesda Car Rental", 1))
    
                Select Case Status
                    Case 1
                        Condition = "Excellent"
                    Case 2
                        Condition = "Good"
                    Case 3
                        Condition = "Drivable"
                    Case Else
                        Condition = "Unknown"
                End Select
    
                If (Status < 1) Or (Status > 3) Then
                    MsgBox("Please enter a valid number between 1 and 3",
                           MsgBoxStyle.Information Or MsgBoxStyle.OkOnly,
                           "Bethesda Car Rental")
                End If
            Loop Until (Status > 0) And (Status < 4)
    
            Return Condition
        End Function
    
        Private Function GetTankLevel() As String
            Dim Level As Integer
            Dim Result As String
    
            Do
                Level = CInt(InputBox("Enter Tank Level:" & vbCrLf &
                                         "1. Empty" & vbCrLf &
                                         "2. 1/4 Empty" & vbCrLf &
                                         "3. 1/2 Full" & vbCrLf &
                                         "4. 3/4 Full" & vbCrLf &
                                         "5. Full",
                                         "Bethesda Car Rental", 1))
                Result = Microsoft.VisualBasic.Switch(Level = 1, "Empty",
                                                       Level = 2, "1/4 Empty",
                                                       Level = 3, "1/2 Full",
                                                       Level = 4, "3/4 Full",
                                                       True, "Full")
                If (Level < 1) Or (Level > 5) Then
                    MsgBox("Invalid tank level. " &
                           "Please try again.",
                           MsgBoxStyle.Information Or MsgBoxStyle.OkOnly,
                           "Bethesda Car Rental")
                End If
            Loop While (Level < 1) Or (Level > 5)
    
            Return Result
        End Function
    
        Public Function Main() As Integer
            Dim EmployeeName As String
            Dim CustomerName As String
            Dim TagNumber As String, CarSelected As String
            Dim CarCondition As String
            Dim TankLevel As String
            Dim RentStartDate As Date, RentEndDate As Date
            Dim NumberOfDays As Integer
            Dim RateType As String, RateApplied As Double
            Dim OrderTotal As Double
            Dim OrderInvoice As String
            Dim Answer As MsgBoxResult
    
            RateApplied = 0
            RateType = "Weekly Rate"
            OrderTotal = RateApplied
    
            Do
                EmployeeName = GetEmployeeName()
    
                CustomerName = InputBox("Enter Customer Name:", _
                                               "Bethesda Car Rental", "John Doe")
                TagNumber = InputBox("Enter the tag number of the car to rent:",
                                               "Bethesda Car Rental", "000000")
    
                CarSelected = Microsoft.VisualBasic.Switch(
                            TagNumber = "297419", "BMW 335i",
                            TagNumber = "485M270", "Chevrolet Avalanche",
                            TagNumber = "247597", "Honda Accord LX",
                            TagNumber = "924095", "Mazda Miata",
                            TagNumber = "772475", "Chevrolet Aveo",
                            TagNumber = "M931429", "Ford E150XL",
                            TagNumber = "240759", "Buick Lacrosse",
                            True, "Unidentified Car")
    
                CarCondition = GetCarCondition()
    
                TankLevel = GetTankLevel()
    
                RentStartDate = CDate(InputBox("Enter Rent Start Date:",
                                               "Bethesda Car Rental",
                                                #1/1/1900#))
                RentEndDate = CDate(InputBox("Enter Rend End Date:",
                                               "Bethesda Car Rental",
                                                #1/1/1900#))
    
                If RentEndDate < RentStartDate Then
                    MsgBox("The values you entered for the start and end dates " &
                           "are not consecute. The rent start date must occur " &
                           "prior to the rent end date",
                           MsgBoxStyle.Critical Or MsgBoxStyle.OkOnly,
                           "Bethesda Car Rental")
                    GoTo RestartOrderProcessing
                End If
    
                NumberOfDays = DateDiff(DateInterval.Day, RentStartDate, RentEndDate)
    
                RateApplied = CDbl(InputBox("Enter Rate Applied:", _
                                               "Bethesda Car Rental", 0))
    
                Dim TemporaryRate As Double
    
                Select Case NumberOfDays
                    Case 0, 1
                        RateType = "Daily Rate"
                        OrderTotal = RateApplied
                    Case 2
                        RateType = "Weekend Rate"
                        TemporaryRate = RateApplied * 50 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * 2
                    Case 2 To 7
                        RateType = "Weekly Rate"
                        TemporaryRate = RateApplied * 25 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * NumberOfDays
                    Case Is > 8
                        RateType = "Monthly Rate"
                        TemporaryRate = RateApplied * 15 / 100
                        RateApplied = RateApplied - TemporaryRate
                        OrderTotal = RateApplied * NumberOfDays
                End Select
    
                OrderInvoice = "===========================" & vbCrLf &
                          "=//= BETHESDA CAR RENTAL =//=" & vbCrLf &
                          "==-=-= Order Processing =-=-==" & vbCrLf &
                  "------------------------------------------------" & vbCrLf &
                          "Processed by:" & vbTab & EmployeeName & vbCrLf &
                          "Processed for:" & vbTab & CustomerName & vbCrLf &
                  "------------------------------------------------" & vbCrLf &
                          "Car Selected:" & vbCrLf &
                          vbTab & "Tag #:" & vbTab & TagNumber & vbCrLf &
                          vbTab & "Car:" & vbTab & CarSelected & vbCrLf &
                          vbTab & "Tank:" & vbTab & TankLevel & vbCrLf &
                          "Car Condition:" & vbTab & CarCondition & vbCrLf &
                  "------------------------------------------------" & vbCrLf &
                          "Start Date:" & vbTab & RentStartDate & vbCrLf &
                          "End Date:" & vbTab & RentEndDate & vbCrLf &
                          "Nbr of Days:" & vbTab & NumberOfDays & vbCrLf &
                  "------------------------------------------------" & vbCrLf &
                          "Rate Type:" & vbTab & RateType & vbCrLf &
                  "Rate Applied:" & vbTab & FormatCurrency(RateApplied) & vbCrLf &
                  "Order Total:" & vbTab & FormatCurrency(OrderTotal) & vbCrLf &
                          "==========================="
    
                MsgBox(OrderInvoice,
                          MsgBoxStyle.Information Or MsgBoxStyle.OkOnly,
                       "Bethesda Car Rental")
    
    RestartOrderProcessing:
                Answer = MsgBox("Do you want to process another order?",
                                MsgBoxStyle.Information Or MsgBoxStyle.YesNo,
                                "Bethesda Car Rental")
            Loop Until Answer = MsgBoxResult.No
                Return 0
        End Function
    
    End Module
  5. Execute the application
  6. Enter the employee number as 92746, the customer name as James Wiley, the tag number as 297419, the car condition as 1, the tank level as 5, the start date as 11/07/2008, the end date as 11/10/2008, and the rate applied 49.95
  7. When asked whether you want to process another order, click Yes
  8. Enter the employee number as 54080, the customer name as Sunil Ajat, the tag number as 240759, the car condition as 3, the tank level as 3, the start date as 11/05/2008, the end date as 11/15/2008, and the rate applied 70.25
  9. When asked whether you want to process another order, click Yes
  10. Enter the employee number as 22804, the customer name as George Livingstone, the tag number as 924095, the car condition as 2, the tank level as 4, the start date as 09/15/2008, the end date as 09/19/2008, and the rate applied 65.75
  11. When asked whether you want to process another order, click Yes
  12. Enter the employee number as 86285, the customer name as Antoinette D. Liel, the tag number as 485M270, the car condition as 2, the tank level as 2, the start date as 11/15/2008, the end date as 11/17/2008, and the rate applied 55.50
  13. When asked whether you want to process another order, click No
  14. Close the message box and the DOS window to return to your programming environment

Combinations of Disjunctions

As opposed to evaluating only two conditions, you may face a situation that presents three of them and must consider a combination of more than two conditions. You would apply the same logical approach we reviewed for the logical conjunction, except that, in a group of logical disjunctions, if one of them is true, the whole statement becomes true.

 
 
   
 

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