Visual Basic Programming

Page 12

As you may recall on Page 9, Visual Basic can test values and return something depending on the result. Another form of this selection process is the Select Case structure. This allows the programmer to choose certain conditions depending on the value of a user input (text box, etc.) or of a variable. In this exercise, we will design a tax withholdings calculator as seen above to demonstrate this method.

• Open a new project and name the Project Cases with the project's Name property.

  • Select the project icon in the Project Explorer window, then type the name in the properties window.

• Next, select the form and name the form frmCases with the form's name property in the properties window.
• Set the BorderStyle property to 1-Fixed Single, then the MinButton property to True.
• Set the form's Caption to Tax Calculator. or whatever you want.
• Adjust the objects as shown above.
  • Name the textbox txtIncome.
  • Name the label to the left of the textbox lblIncome.
  • Name the label below lblWithholdings.
  • Name the label to the right lblTotal.
  • Name the label below lblWithholdings lblNetIncome.
  • Name the label to the right lblTotalNetIncome.
  • Name the command buttons as follows from left to right:
    • cmdCalc
    • cmdClear
    • cmdExit
  • Set the command button's captions as seen above. Notice the access keys.
  • Lock the controls.

Now to code the application:

• Code the cmdExit button to end the application.
• Code the cmdClear button to clear txtIncome and lblTotal.

  txtIncome.Text = ""
  lblTotal.Caption = ""
  

• Click on the object box and click on General to open the General Declarations section of the code window.
• Type Dim lngIncome as Long.
• Press Enter, then type Dim lngWithholding as Long
• Press Enter again.

The code above simply declares form-level variables named lngIncome and lngWithholding as the Long.

The lng prefix to Income is just an identifier to remind the programmer what type of variable they are using (in this case Long). We did not do that previously, but it is not necessary. Any serious programmer heavy into programming principles would debate that passionately, but I just want to try to teach you how to do it. I know plenty of people who do not care about most of the principals of programming. The principles will only become partially important when and if you decide to do this for a company. Now we will continue.

• Go to the cmdCalc sub-procedure code window.
• Press tab, then type the following line:

  lngIncome = txtIncome.Text 'Assigns txtIncome.Text (the text in textbox txtIncome) to the variable lngIncome
  
  

• Press Enter.

Now we will begin our Case statement.

• Type the following lines

  Select Case lngIncome 'Opens the selection process using the variable lngIncome. Tests the variable for all the following cases.
      Case 0 To 4000 'Sets the range of values for lngIncome; in this case, 0 to 4000
          lngWithholding = txtIncome.Text * 0 'No tax; lngWithholding will equal 0.
      End Select 'Ends the select case statements
      lblTotal.Caption = Format(lngIncome, "Currency") 'Formats resulting value for lngIncome in dollars and cents

This code will not tax anything equal to or below 4000 dollars. Refer to the comments to understand code if necessary.

• Now for our next case, type the following lines above the End Select line.

  Case 4001 To 15000 'Sets the range of values for lngIncome; in this case, 4001 to 15000.
      lngWithholding = txtIncome.Text * .04

This code multiplies the text in txtIncome by .04, then assigns the value to the variable lngWithholding.

Now to finish this program off. Just remember that the Case statement that sets the range determines the decimal, or percentage, that txtIncome.Text will be multiplied by.

• Type in the following Cases above the End Select line:

  Case 15001 To 39999
      lngWithholding = lngIncome * .06
  Case 40000 To 59999
      lngWithholding = lngIncome * 0.1
  Case 60000 To 79999
      lngWithholding = lngIncome * 0.14
  Case 80000 To 99999
      lngWithholding = lngIncome * 0.2
  Case 100000 To 129999
      lngWithholding = lngIncome * 0.27
  Case Is >= 130000 'Just says when Case Is greater than or equal to 130000, multiply as follows
      lngWithholding = lngIncome * 0.3

Try testing the application now if you would like.

I hope you enjoyed this study in cases. Now it is time to move on to Page 13.

How do you like this tutorial? Are you learning this language easily? Please let me know via e-mail at webtechjava@yahoo.com.

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