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Programming in Visual Basic

Sharing Data :

All the data we have used so far has been conveniently contained within controls on a form. This has meant that we can use the name of the control (txtQuantity, txtPrice, txtTotal, etc.) to refer to the data that is contained within those controls.

There are often times when we need to use variables data that is not contained in a control. Typical examples would be - to move data from one control to another, to move data from one form to another, as a temporary store during calculations and holding information for decision making.

To allow data to be shared between controls within a for, we declare the name of the data (and usually its data type) in the General Declarations section of the form's code. The general format of the declaration is

Dim data name as data type

For example:

Dim OldPrice As Integer

defines a new variable (data that can be changed troughout the program) called OldPrice that can only hold integer (whole number) values.

Dim Student As String

defines a new variable called Student that will hold text strings.

If you wish to define a constant item of data (one that holds the same value throughout) that is shared by controls within a form, we make a declaration using Const instead of Dim. For example:

Const VATRate = 17.5 defines a data item called VARRate which always has the value 17.5

Check Boxes :

Check Boxes only have two values 0 or 1, depending wether they are unchecked or checked. We can clear a check box by setting a-its value to 0 (e.g. chkAnswer1 = 0). We can also examine whether or not a check box has been checked or not. For Example:

If chkAnswer1 = 1 Then
   MsgBox ("Correct answer")
   MsgBox("Wrong answer")
End If

Task Nine :

1. Open the Quiz project, re-arrange and add controls so that it is similar to the above.

2. Double click anywhere on the form, avoiding the form's controls to bring up the form's code. Choose (general) from the Object list at the top of the form's code and (declarations) from the Proc list. Enter:

Dim QuestionNumber As Integer

This sets up a variable to hold the number of the questions we choose which we will need to know when checking which answer has been chosen.

3. As each question is chosen, we need to ensure that the check boxes are cleared and that the QuestionNumber variable is set to the correct value. Edit the code for the Question 1 command button as follows:

chkAnswer1 = 0
chkAnswer2 = 0
chkAnswer3 = 0
QuestionNumber = 1
txtQuestion = "What do you call a small pice of silicon which has a number of electronic circuits fabricated on it?"
txtAnswer1 = "byte"
txtAnswer2 = "chip"
txtAnswer3 = "port"

4. Edit the code for the Question 2, Question 3 and Question 4 command buttons similarly.

5. We need to write the code for the Check Answer command button. Generally, the message given to the user depends on the Question Number and which Check Box has been chosen. We can use a select Case structure for the question number and an If ... Else ... End If structure for checking the answer given. For question numbers 1 and 2 (Case 1, 2) the second answer (chkAnswer2) is correct, for Question 3 (Case 3) the first answer is correct (chkAnswer1) and for question 4 (Case 4) the third answer is correct (chkAnswer3). Doube click on the Check Answer command button and enter the following code

Select Case QuestionNumber
   Case 1,2
      If chkAnswer2 = 1 Then
         MsgBox ("Well done, that is correct")
         MsgBox ("I'm afraid that is the wrong answer")
      End If

6. Enter the code for Case 3 and Case 4, the End Select statement and statements to clear the check boxes after the Select Case structure.

7. Save the project, start the program and test all options to see if your code works.

Exercise Nine :

1. Open the Stock project and add two check boxes labeled VAT and no VAT.

2. Edit the coding of the Calculate command button to see whether or not VAT is payable and carry out the appropriate calculation.

3. Open the Address project and add two check boxes labeled First Name and Surname.

4. Edit the coding for the Find Name command button to make it look for the first or last name of the person entered, dependent on the check boxes, and enter the relevant details. (Make up some first names of your own).

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