Boolean Conjunctions and Disjunctions

Conditional Conjunctions

Nesting a Conditional Statement

In the body of the conditional statement, you can create another conditional statement. This is referred to as nesting the condition.

Practical Learning: Nesting a Conditional Statement

1. Start Microsoft Access
2. In the list of files, click Business Mathematics database from the previous lesson
3. In the Navigation Pane, right-click Loan Decision2 and click Design View
4. On the form, right-click the Decide button and click Build Event...
5. In the Choose Builder dialog box, click Code Builder and click OK
6. Implement the event as follows:

   Private Sub cmdDecide_Click()
       Dim decision As String
       Dim creditScore As Integer
   
       If IsNumeric(txtCreditScore) Then
           creditScore = CInt(Nz(txtCreditScore))
   
           If creditScore >= 650 Then
               decision = "Loan Approved"
           ElseIf creditScore >= 550 Then
               decision = "We will need 2 professional and 3 personal references."
           Else
               decision = "Loan Denied"
           End If
       End If
       
       txtDecision = decision
   End Sub

7. Return to Microsoft Access and switch the to Form View
8. Click the Decide button

   

9. Click Customer Credit Store and type 428
10. Click the Decide button

    

11. Click Customer Credit Store and type 568
12. Click the Decide button

    

13. Click Customer Credit Store and type 685
14. Click the Decide button

    

15. Save and close the form

Nesting an Immediate If Function

To get the functionality of an If...Then...ElseIf... conditional statement, you can nest one IIf() function in another. In reality, you would call the IIf() function in place of the FalsePart of another IIf() function. The nesting can be resolved as follows:

Function IIf(ByVal Expression As Boolean, 
             ByVal TruePart As Object,
             Function IIf(ByVal Expression As Boolean,
			  ByVal TruePart As Object,
			  Function IIf(ByVal Expression As Boolean,
				       ByVal TruePart As Object, 
				       Function IIf(ByVal Expression As Boolean,
						    ByVal TruePart As Object,
						    ByVal FalsePart As Object
				       ) As Object
			  ) As Object
	     ) As Object
) As Object

By nesting IIf() calls, a long expression like the following can be written in one line:

Private Sub FirstName_LostFocus()
    If FirstName = "" Then
        If LastName = "" Then
            FullName = ""
        Else
            FullName = LastName
        End If
    Else
        FullName = LastName & ", " & FirstName
    End If
End Sub

Practical Learning: Nesting an Immediate If Function

1. In the Navigation Pane, right-click Compound Interest1 and click Design View
2. On the form, right-click the Calculate button and click Build Event...
3. In the Choose Builder dialog box, double-click Code Builder and implement the event as follows:

   Private Sub cmdCalculate_Click()
       Dim factor
       Dim principal
       Dim futureValue
       Dim interestRate
       Dim interestEarned
       Dim periods As Integer
       Dim compounded As Integer
       Dim compoundFrequency As Integer
   
       principal = CDbl(Nz(txtPrincipal))
       interestRate = CDbl(Nz(txtInterestRate)) / 100#
       periods = CInt(Nz(txtPeriods))
   
       compounded = CInt(InputBox("Enter a number for the desired compound frequency:" & vbCrLf & _
                                  "1 - Daily" & vbCrLf & _
                                  "2 - Weekly" & vbCrLf & _
                                  "3 - Monthly" & vbCrLf & _
                                  "4 - Quarterly" & vbCrLf & _
                                  "5 - Semiannually" & vbCrLf & _
                                  "6 - Anually", _
                                  "Compound interest", "1"))
       compoundFrequency = iif(compounded = 1, 365, iif(compounded = 2, 52, iif(compounded = 3, 12, iif(compounded = 4, 4, iif(compounded = 5, 2, 1)))))
       factor = iif(compounded = 1, interestRate / 365, _
                  iif(compounded = 2, interestRate / 52, _
                    iif(compounded = 3, interestRate / 12, _
                      iif(compounded = 4, interestRate / 4, _
                        iif(compounded = 5, interestRate / 2, interestRate) _
                      ) _
                    ) _
                  ) _
                )
   
       futureValue = principal * ((1# + factor) ^ (periods * compoundFrequency))
       interestEarned = futureValue - principal
   
       txtCompounded = iif(compounded = 1, "Compounded Daily", _
                       iif(compounded = 2, "Compounded Weekly", _
                       iif(compounded = 3, "Compounded Monthly", _
                       iif(compounded = 4, "Compounded Quarterly", _
                       iif(compounded = 6, "Compounded Semi-Annually", _
                                           "Compounded Anually")))))
       txtInterestEarned = FormatNumber(interestEarned)
       txtFutureValue = FormatNumber(futureValue)
   End Sub

4. Return to Microsoft Access and switch the to Form View

   

5. Click Principal and type 8500
6. Click Interest Rate and type 4.25
7. Click Periods and type 10
8. Click the Calculate button
9. In the input box, type 3

   

10. Click OK

    

11. Click the Calculate button
12. In the input box, type 8 and press Enter

    

13. Save and close the form

Boolean Conjunctions

When you nest one condition in another condition as in:

If condition1 = True	  ' The first or external condition
    If condition2 = True  ' The second or internal condition
	statement(s)
    End If
End If

you are in fact saying "If condition1 verifies, Then if condition2 verifies, do this...". To support  a simplified version of this scenario, the Visual Basic language provides the Boolean conjunction operator named And. Its primary formula is:

condition1 And Condition2
    statement(s)

You must formulate each condition to produce a true or a false result. The result is as follows:

• If condition1 is True AND condition2 is True, the whole expression produces a true result. Here is an example:

   Sub Calculate()
          Dim principal As Double, commission As Double
          Dim numberOfShares As Integer, pricePerShare As Double
  
          numberOfShares = CInt(TxtNumberOfShares)
          pricePerShare = CDbl(TxtPricePerShare)
  
          principal = numberOfShares * pricePerShare
  
          If principal >= 0.00 And principal <= 2500.00 Then
              commission = 26.25 + (principal * 0.0014)
          End If
  End Sub

• If either condition1 or condition2 is false (including if both are false), the whole expression produces a false result

To make your code easier to read, it is a good idea to include each Boolean operation in its own parentheses.

Practical Learning: Creating and Using Boolean Conjunctions

1. In the Navigation Pane, right-click Brokerage Company1 and click Design View
2. On the form, right-click the Calculate button and click Build Event...
3. In the Choose Builder dialog box, double-click Code Builder and implement the event as follows:

   Private Sub cmdCalculate_Click()
       Dim principal As Double, commission As Double
       Dim numberOfShares As Integer, pricePerShare As Double
   
       numberOfShares = CInt(Nz(txtNumberOfShares))
       pricePerShare = CDbl(Nz(txtPricePerShare))
   
       principal = numberOfShares * pricePerShare
   
       If principal = 0# Then
           commission = 0#
       End If
   
       If (principal > 0#) And (principal <= 2500#) Then
           commission = 26.25 + (principal * 0.0014)
       End If
           
       If (principal > 2500#) And (principal <= 6000#) Then
           commission = 45# + (principal * 0.0054)
       End If
           
       If (principal > 6000#) And (principal <= 20000#) Then
           commission = 60# + (principal * 0.0028)
       End If
           
       If (principal > 20000#) And (principal <= 50000#) Then
           commission = 75# + (principal * 0.001875)
       End If
           
       If (principal > 50000#) And (principal <= 500000#) Then
           commission = 131.25 + (principal * 0.0009)
       End If
           
       If (principal > 500000#) Then
           commission = 206.25 + (principal * 0.000075)
       End If
   
       txtPrincipal = FormatNumber(principal)
       txtCommission = FormatNumber(commission)
       txtTotalInvestment = FormatNumber(principal + commission)
   End Sub

4. Return to Microsoft Access and switch the to Form View

   

5. Click Number of Shares and type 1500
6. Click Price per Share and type 48.75

   

    

7. Click Calculate

   

8. Click the Calculate button
9. In the input box, type 8 and press Enter
10. Save and close the form

Creating Many Conjunctions

Depending on your program, if two conditions are not enough, you can create as many conjunctions as you want. The formula to follow is:

condition1 And condition2 And condition3 And . . . And condition_n

When the expression is checked, if any of the operations is false, the whole operation is false. The only time the whole operation is true is if all of the operations are true.

Of course, you can nest a Boolean condition inside another conditional statement.

Boolean Disjunctions

Introduction

A Boolean disjunction is a combination of conditions where only one of the conditions needs to be true for the whole operation to be true. This operation is performed using the Boolean disjunction operator represented as Or. The primary formula to follow is:

condition1 Or condition2

The operation works as follows:

• If at least one of condition1 OR condition2 is true, the whole operation is true
• If both conditions are false, only then will the whole operation produce a false result

Combining Conjunctions and Disjunctions

Conjunctions and disjunctions can be used in the same expression. A conjunction (or disjunction) can be used to evaluate one sub-expression while a disjunction (or conjunction) can be used to evaluate another sub-expression.

As seen previously, one way you can combine conditional statements is by nesting them.

Practical Learning: Ending the Lesson

• Close Microsoft Access