Private Sub cmdCondition_Click()
    Dim Number As Integer

    For Number = 1 To 6
        MsgBox Number
    Next
End Sub

1. Start Microsoft Access
2. From the resources that accompany these lessons, open the Bethesda Car Rental2 database
3. In the Navigation Pane, right-click New ExistingRentalOrder and click Design View
4. On the form, double-click the Mileage End text box
5. In the Properties window, click Event and double-click On Lost Focus
6. Click its ellipsis button and implement the event as follows:
   

   Private Sub txtMileageEnd_LostFocus()
       If IsNull(txtMileageEnd) Then
           MsgBox "You must enter the ending mileage."
           Exit Sub
       Else
           txtTotalMileage = Nz(txtMileageEnd) - Nz(txtMileageStart)
       End If
   End Sub

7. In the Object combo box, select txtEndDate
8. In the Procedure combo box, select LostFocus and implement the event as follows:
   

   Private Sub txtEndDate_LostFocus()
       If IsNull(txtEndDate) Then
           MsgBox "You must enter the ending date."
           Exit Sub
       Else
           txtTotalDays = DateDiff("d", CDate(txtStartDate), CDate(txtEndDate))
       End If
   End Sub

9. In the Object combo box, select txtRateApplied
10. In the Procedure combo box, select LostFocus and implement the event as follows:
    

    Private Sub txtRateApplied_LostFocus()
        If IsNull(txtRateApplied) Then
            MsgBox "You must enter the rate applied."
            Exit Sub
        Else
            txtSubTotal = Nz([txtRateApplied]) * Nz([txtTotalDays])
        End If
    End Sub

11. In the Object combo box, select txtTaxRate
12. In the Procedure combo box, select LostFocus and implement the event as follows:
    

    Private Sub txtTaxRate_LostFocus()
        If IsNull(txtTaxRate) Then
            MsgBox "You must enter the tax rate."
            Exit Sub
        Else
            txtTaxAmount = CLng(Nz([txtSubTotal]) * Nz([txtTaxRate]) * 100) / 100
            txtRentTotal = Nz([txtSubTotal]) + Nz([txtTaxAmount])
        End If
    End Sub

13. Return to Microsoft Access
14. Close the form
15. When asked whether you want to save, click Yes

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 procedure:

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

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 interpreter 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:

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

This time, when the program runs, the procedure would be accessed and would start displaying the message boxes. After displaying two, the Exit Sub would ask the interpreter 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.

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:

Private Sub cmdCondition_Click()
    Dim Number As Integer

    For Number = 1 To 12
        MsgBox Number

        If Number = 4 Then
            Exit For
        End If
    Next
End Sub

When this program executes, it is supposed to display numbers from 1 to 12, 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 interpreter would stop the flow of For and continue with code after the Next keyword.

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.

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

Private Sub cmdCondition_Click()
    Dim TypeOfHouse As String
    Dim Choice As Integer
    Dim Value As Double
        
    TypeOfHouse = "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?"))

    TypeOfHouse = Choose(Choice, "Single Family", _
                                 "Townhouse", _
                                 "Condominium")
End Sub

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

Private Sub cmdCondition_Click()
    Dim TypeOfHouse As String
    Dim Choice As Integer
    Dim Value As Double
        
    TypeOfHouse = "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?"))

    TypeOfHouse = Choose(Choice, "Single Family", _
                                 "Townhouse", _
                                 "Condominium")

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

Here is an example of running the program:

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:

Private Sub cmdCondition_Click()
    Dim TypeOfHouse As String
    Dim Choice As Integer
    Dim Value As Double
        
    TypeOfHouse = "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?"))

    TypeOfHouse = Choose(Choice, "Single Family", _
                                 "Townhouse", _
                                 "Condominium")
                                 
    If Choice = 1 Then
        MsgBox ("Desired House Type:      " & vbTab & TypeOfHouse & 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
End Sub

Using conditional nesting, we have seen how you can write one conditional statement 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 you 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:

Private Sub cmdCondition_Click()
    Dim TypeOfHouse As String
    Dim Choice As Integer
    Dim Value As Double

    TypeOfHouse = "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?"))

    TypeOfHouse = Choose(Choice, "Single Family", _
                                 "Townhouse", _
                                 "Condominium")

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

Here is an example of running the program:

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:

Private Sub cmdCondition_Click()
    . . . No Change

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

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:

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

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 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:

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:

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:

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:

These four tables can be resumed as follows:

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