Software Development

Activity A

If-Else Example - Ending a Program

Here is an example of an If-Else statement that asks the user if they really want to end the program or not.

1. Open Visual Basic.
2. Save the form and project to a new folder called If_Example
3. Add a command button to your form. Change the button's caption to Exit. Change the button's name to cmdExit. Like my form which is shown below.
   
4. Copy the code below into the form's coding window.
5. Run the program

The code is between the dotted lines below
.....................................................

Private Sub cmdExit_Click()

    Dim Response As Integer

    Response = MsgBox("Exit Program?", vbInformation + vbYesNo, "Title")

    If Response = vbYes Then

        End

    ElseIf Response = vbNo Then

        Me.Refresh

    End If

End Sub

.....................................................

Extension Work:

1. Change the MsgBox code " Exit Program?" so a different message is displayed to the user.
     
2. Change the MsgBox title to something better. For example, you could change it from "Title" to "Query Exit "
    
3. To help you understand the code better, add a breakpoint to the line -- >
    
       Private Sub cmdExit_Click()
   
   Run the program, click the Exit button and and then press F8 to step through the code line by line.

Activity B

If-Else Example - Calculator

This example program uses If-Else statements to check which option button is selected, Add, Subtract, Multiply or Divide.

1. Add the controls shown above to the form you created for Activity A.
2. Change the names of the controls to:-

   txtFirstNum
txtFirstNum
txtAnswer
optAdd
optSubtract
optMultiply
optDivide
cmdCalc
cmdExit

3. Copy the code given below into the form's coding window.
4. Run the program

The code is between the dotted lines below
.....................................................

Private Sub cmdCalc_Click()
    Dim firstNum As Double
    Dim secondNum As Double
    Dim answer As Double

    firstNum = txtFirstNum.Text   'get first number from textbox
    secondNum = txtSecondNum.Text   'get second number from textbox

    If optAdd.Value = True Then   'if the Add option button is selected
        answer = firstNum + secondNum
    ElseIf optSubtract.Value = True Then 'if Subtract option button is selected
        answer = firstNum - secondNum
    ElseIf optMultiply.Value = True Then 'if Multiply option button is selected
        answer = firstNum * secondNum
    ElseIf optDivide.Value = True Then   'if Divide option button is selected
        answer = firstNum / secondNum
    Else     'if the user forgot to select an option
        MsgBox "Please choose an option button"
        Exit Sub
    End If

    txtAnswer.Text = answer  'Display the answer in the answer textbox

End Sub

.....................................................

Extension Work:

1. One problem you will find with the program is that it will crash if the user does not enter any numbers into the two textboxes. Here is some code that helps correct that:-
   
   Replace the line...
   
       firstNumber = txtFirstNumber.Text
   
   with these lines...
   
   If IsNumeric(txtFirstNum.Text) Then    'if there is a number in the textbox
       firstNum = txtFirstNum.Text       'get the number from the textbox
   Else  'otherwise, inform user to put a number in the textbox, then exit the sub
       MsgBox "Please enter a number into the 'First Number' textbox"
       Exit Sub
   End If
   
   
2. Now that you have been shown how to check that a number has been entered into the first textbox, add code to check that a number has been entered into the second textbox as well.
     
3. To help you understand the code better, add a breakpoint to the line -- >
    
       Private Sub cmdCalc_Click()
   
   Run the program, click the Calculate button and and then press F8 to step through the code line by line.
   

Activity C

For-Next Example - Times Table

This example program uses a For-Next looping statement to display the two times table in a listbox.

1. Open Visual Basic.
2. Save the form and project to a new folder called Loop_Example
3. Add a listbox and a command button to your form as shown above.
4. Change the names of the controls to:-

   lstTimesTable
cmdTimesTable

5. Copy the code given below into the form's coding window.
6. Run the program

The code is between the dotted lines below
.....................................................

Private Sub cmdTimesTable_Click()

    Dim i As Integer
    Dim lineToDisplay As String
    lstTimesTable.Clear

    For i = 1 To 10
        lineToDisplay = i & " times 2 is " & (i * 2)
        lstTimesTable.AddItem lineToDisplay
    Next

End Sub

.....................................................

Extension Work:

1. Change the code above to display more than 10 lines of the 2 times table, say 20 lines.
     
   
2. Now change the code above to display the 3 times table.
     
3. To help you understand the code better, add a breakpoint to the line -- >
    
       Private Sub cmdTimesTable_Click()
   
   Run the program, click the cmdTimesTable button and and then press F8 to step through the code line by line.
     
4. How about adding option buttons so the user can specify the times table they want displayed. Like the form shown below.




To do this, add four option buttons and name them appropriately. for example, optTwo, optThree etc.

You will need to add If-Else code, similar to the code you used in Activity B. To start you off, find this line ...

    Dim lineToDisplay As String line

and insert the following code after it

Add this code after the line -- > Dim lineToDisplay As String
.....................................................

Dim multiplier As Integer

If optTwo.Value = True Then
    multiplier = 2
End If

.....................................................

Now change the line...

        lineToDisplay = i & " times 2 is " & (i * 2)
to

        lineToDisplay = i & " times " & multiplier & " is " & (i * multiplier)

This If-Else code only checks to see if the first option button is selected. What if the user selects one of the other option buttons? Add more code to check for this. Look at Activity B again if you don't know how to do it.