Visual Basic Programming - The Variables Program

Ross Sheppard High School
Computer Programming 20
Student Learning Guide
The Variables Program

	When you have finished this project, you will be able to:
	declare a variable
	describe different types of variable
	use a variable
	describe the following terms: variables declare integer string

Create a new folder called Variables on your personal drive.

The illustration below shows the visual implementation for the Variables Program.

The Variables Program

The user will enter two different numbers; one in each of the two TextBoxes, txtNum1 and txtNum2. When the SumIt! button btnSumIt is pressed the answer will appear in the TextBox txtAnswer. When the CommandButton btnExit is pressed the program will end.

Start a new Standard.exe project in Visual Basic.

Use the table below for the visual implementation of the Variables program:

Object	Property	Setting
Form	Name	frmVariables
	Caption	The Variables Program
TextBox	Name	txtAnswer
	Text	Make it blank
	Font	Ms Sans Serif Bold 18pt
TextBox	Name	txtNum1
	Text	Make it blank
	Font	Ms Sans Serif Bold 18pt
TextBox	Name	txtNum2
	Text	Make it blank
	Font	Ms Sans Serif Bold 18pt
Label	Name	lblSign
	Caption	+
	Font	Ms Sans Serif Bold 18pt
	Alignment	2- Center
CommandButton	Name	btnSumIt
	Caption	Sum It!
	Font	Your choice
CommandButton	Name	btnExit
	Caption	Exit
	Font	Your choice

Save this project in the Variables Program folder as Variables Program. It should look similar to the illustration below:
Add the following comment to the General_Delcarations() area of your form:
Now it is time to enter the code for the Variables Program. Start by entering the code for the Exit Button:
When you have input from the user in a program, you require a variable. You also require a variable anytime anything in the program changes. In the Hello World project there were no variables, so you didn't need to learn to work with them. However, this program does have variables. Do you know what the variables are?
Go to the Code View window of your Variables Program project.
In the left hand box of the Code View, select General and in the right hand box select Declarations. The General Declarations is where code that applies to the entire program is placed. In this case you will write code that requires all variables to be declared, thus preventing mistakes when you run the program.
Enter the following code:
The Option Explicit statement means that Visual Basic will not accept any varibles that have not been declared. Using this statement is good programming convention and will save you many hours of trouble shooting later on.
To ensure this statement is added to every new project, click on Tools in the Menu Bar then Options . . .
The window shown below will appear; check the Require Variable Declaration as shown in the illustration below:
Next, declare the variables that the user will enter in the TextBoxes txtNum1 and txtNum2.
The variables will be used when the CommandButton btnSumIt is pressed. Therefore, the variables should be declared during that event.
In the View Code window, select the btnSumIt_(Click) procedure and enter the following code:
Save your Variable Program and run it. Does it work?

A note about variables:
- variables are used to represent data that changes
- a variable is actually a memory location
- the variable type tells the computer how much memory to allocate
- a variable is given a name
- a variable is referenced by the name given
Syntax for declaring a variable:

Dim varName As Datatype
Where:
- Dim = Dimension or the size of the memory allocation for the variable
- varName = the name of the variable
- Datatype = the type of variable; integer for example

In addition to the Integer variable there are a number of other types as shown in the table below:

Variable Type	Code	Example
Integer	Whole numbers 2 bytes allocated	Integer to hold a person's age Dim nAge As Integer
Long	Whole numbers 4 bytes allocated	Long number to count the population of Canada Dim nCanadianPopulation As Long
Single	Decimal	Decimal point number to answer a math problem Dim sAnswer As Float
Double	Decima to 12 digits of accuracy	Double to record salaries Dim fSalary As Double
Boolean	True/False statements	Boolean as in if you pass this course or not Dim bPassed As Boolean
String	Text Data	String to hold your name Dim strFirstName As String

When a user first starts a program it is expected that the cursor will be in the first place that data will need to be entered. In the case of your Variables Program, the user is expected to enter a number into the TextBox txtNum1.
When the Variables Program is first started, it may not default to the txtNum1 TextBox, so as a programmer, you must set the place where the cursor starts. This is called setting the Focus.
For this project, you will set the focus during the loading of the form using the TabIndex procedure. Go to the Code View window. Create a new sub by selecting Form in the object box and Load in the Procedure box.
This will add a new sub to the code window:
Add the following code to make the txtNum1 TextBox as the place where the cursor will appear when the form loads:
While you are at it, add the code so that when the user presses the Tab key, the focus will change to the txtNum2 TextBox.
Note that you could also set the tab order when you create the object by changing it in the properties box:
For all projects that you create in Visual Basic, you will be expected to set the focus in the appropriate place.
Write the pseudo-code for the Variables Program directly in your program as comments.
Be sure to add the tool tips to this and all subsequent programs.
Click here to see the marking guide for the project.
When you have finished, send an email to your teacher asking that this project be marked.