1. Chapter 3 Programming Fundamentals
Exploring Microsoft Visual Basic 6.0 3
Chapter 3 Programming Fundamentals
Writing Code
Exploring Microsoft Visual Basic 6.0 Copyright © 1999 Prentice-Hall, Inc.
By Carlotta Eaton
Copyright 1999 Prentice-Hall, Inc.

2. Copyright 1999 Prentice-Hall, Inc.
Objectives...
1. Use the Sub command to create event procedures and general procedures
2. Use variables and differentiate data types
3. Differentiate between a variable and a constant
4. Differentiate between Dim and Static statements
5. Use help to find appropriate predefined function, and then utilize the function
Exploring MS Visual Basic 6
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Objectives
6. Convert an algebraic formula to a Visual Basic statement; Write a program that calculates
7. Use the If...Then or Select Case statements to write code that makes decisions
8. Write code that repeats using Do...Loop, For...Next, or For Each ...Next looping statements
Exploring MS Visual Basic 6
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4. Modules and Procedures
Code - the man behind the curtain
Modules - large units of code that comprise a Visual Basic application
Form Modules - contains a form and code for the form
Standard Modules - contains code that is typically used by other modules
Exploring MS Visual Basic 6
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5. Modules and Procedures
Procedures - smaller units that comprise a module
Event procedure - automatically invoked by an event
General procedure - explicitly invoked by another procedure
Private procedure - accessible from within a module
Public procedure - accessible from anywhere
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The Code Editor Window
View and edit code
Views
Full Module View
Procedure View
Features
Auto List Members
Auto Quick Info
Auto Syntax Check
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The Code Editor Window
Object List Box
Procedure List Box
Full Module View button
Auto List Members
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The Code Editor Window
Help window
Syntax error in Red
Procedure view button
Error message box
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Syntax Boxes
Syntax for a Visual Basic statement is shown in a syntax box
Reserved words are shown in bold
Programmer named words are shown in italics
See next slide for an example
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The Sub Statement
Private Sub controlname_eventname( )
Statements
End Sub
Where
Private is the default procedure type
Sub indicates beginning of procedure
controlname is name of associated control
_ (underscore) required separator
eventname is name of corresponding event
( ) set of parentheses is required
End Sub indicates end of a procedure
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The Sub Statement
Example
Private Sub cmdCalcTriangle_Click
Dim Base As Single
Dim Height As Single
Area = 1 / 2 * (Base * Height)
End Sub
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12. Declarations, Variables, and Constants
Variable - a uniquely named storage location that contains data that changes during program execution
Constant - a uniquely named storage locations that contains data that does not change during program execution
Exploring MS Visual Basic 6
Copyright 1999 Prentice-Hall, Inc.

13. Declarations, Variables, and Constants
Rules for Naming Variables
Must begin with an alphabetic character
Can’t contain a period or type-declaration characters such as %, &, !, or $
Must be unique with same scope
Must be no longer than 255 characters
Should not reserved word (See Appendix A)
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Declaring Variables
Declaration statement - nonexecutable code that sets aside storage locations for future use
Local variables - declared within a procedure or function
Global variables - declared in the general section of the application
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Declaring Variables
Declare variables using the Dim or Static statements
Dim statement - value of variable preserved only until procedure ends
Static statement - value of variable preserved the entire time the application is running
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The Dim Statement
Dim variablename As datatype
Where
Dim is required
variablename should be a descriptive name
As is required
datatype is one of the following types:
Boolean, Byte, Date, Integer, Long, Single,
Double, Currency, String, Object or Variant
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Declaring Variables
Data Types
Boolean - True or false
Date - From Jan 1, 100 to Dec 31, 9999
Integer - Numbers without a decimal point
Long - Long integer
Single - Numbers with a decimal point
Double - Long Single
Currency - Dollar amounts
String - Character and alphanumeric data
Object - Any object reference such as Word document
Variant - default, can hold any data type
Exploring MS Visual Basic 6
Copyright 1999 Prentice-Hall, Inc.

18. Assigning Values to Variables
Variablename = value
Where
variablename is the descriptive name of the variable
= is the assignment operator
value is the value the variable will contain
Examples:
Number1 = 5
FirstName = “Steve”
LoanAmount = 67.38
Length = 17.8
Note: Order is important. Variable name always on the left, and value on the right.
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Declaring Constants
Const constantname As datatype = value
Where
Const is required
constantname is the descriptive name of the constant
As is required
datatype is the type of data the constant will contain
= is the assignment operator
value is the value of the constant
Examples:
Const Pi As Single
Const MaxNumber As Integer = 100
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The Wind Chill Project
Write a program that calculates the wind chill temperature
Find a formula - UST Today Weather Web site
Inputs: Wind Speed and Temperature
Outputs: Wind Chill Temperature
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The Wind Chill Project
Orginal formula
WC = (3.71(V **0.5) V)(T )
Visual Basic statement
WC = * (3.71 * Sqr(V) (0.25 * V)) * (T )
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Functions
Function - unit of code that returns a value
Build-in Functions
Sqr - square root
Rnd - random number generator
Int - returns integer portion of a number
Val - converts a string to a value
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Functions
Locating built-in functions
Open the Functions online reference book or search for a function by name
Programmer-written functions
Write your own functions using the Function statement
Exploring MS Visual Basic 6
Copyright 1999 Prentice-Hall, Inc.

24. The Function Statement
Private Function function-name (argument1, argument2....)
statements
End Function
Where
Private or Public is required
Function indicates the beginning of a function
function-name is the name that will be used to call the function
( ) parentheses are required around the argument list
argument1, argument2 are optional variables needed to perform
the calculation or actions needed for the function
End Function indicates the end of the function
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WindChill Function
Private Function WindChill( )
‘Purpose: Calculate the Wind Chill
‘Reference: National Weather Service
Dim V As Integer ‘Wind Speed Velocity
Dim T AS Integer ‘Temperature
V = hsbSpeed.Value
T = hsbTemperature.Value
WindChill = * (3.71 * Sqr(V) _
(0.25*V)) * (T-91.4)+91.4
End Function
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WindChill Function
When the cmdCalculate button is clicked, the WindChill function is executed
Private Sub cmdCalculate_Click()
WC = WindChill()
txtWindChill.Text = Cint(WC)
End Sub
Exploring MS Visual Basic 6
Copyright 1999 Prentice-Hall, Inc.

27. The Wind Chill Project using Functions and Procedures
Hands-On Exercise 1
Create a New Project
Create the Controls for Temperature Input
Create the Controls for Wind Speed Input
Create the Controls for Wind Chill Output
Create the Image Control
Add Banner Comments
Add the Wind Chill Function
Add Temperature and Speed Procedures
Save, Run, Test your Project
Exploring MS Visual Basic 6
Copyright 1999 Prentice-Hall, Inc.

28. Controlling your Application
Sequence
Functions and Procedures
Selection
If...Then...Else statement
Select Case statement
Repetition
For...Next Loop statement
For Each...Next statement
Do Loops
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29. Learning to Add Project
Specification for the Game
purpose of the game is to practice addition skills
use numbers between 0 and 9
user is a pre-school age child, in kindergarten, or in first grade
user may not yet know how to read
game should give visual feedback indicating correct or incorrect answer
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Learning to Add Game
Reward for correct answer
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Learning to Add Game
Image for incorrect answer
Exploring MS Visual Basic 6
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32. Design the User Interface
Prototype - a partially completed version of an application that demonstrates the “look and feel” of the finished product
Usability Testing - end user or client tests design of user interface using a prototype
Exploring MS Visual Basic 6
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33. Making Decisions with the Learning to Add Game
Hands-On Exercise 2
Create the Learning to Add Project
Add Controls to Display the Problem
Set Common Properties
Set Individual Control Properties
Add More Images and Set Properties
Add Picture Box Controls for Icon Buttons
Exploring MS Visual Basic 6
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34. Making Decisions with the Learning to Add Game
Hands-On Exercise 2 (continued)
Add Banner Comments
Add the Load Form Procedure
Add the Checkmark Picture Procedure
Add the Arrow Picture Procedure
Run and Save your Project
Test and Debug your Project
Print your Project Code and Exit
Exploring MS Visual Basic 6
Copyright 1999 Prentice-Hall, Inc.

35. For...Next Loop Structure
For counter = start To end Step increment
statements
Next counter
Where
Counter is tested to see if less than end. If so, repeat loop again. If not, go to statement after Next.
Exploring MS Visual Basic 6
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36. Do While...Loop Structure
Do While condition
statements
Loop
Where
The condition is tested, and if true the loop is repeated. When the condition is false, the loop statements are skipped the statement after Loop is executed.
Exploring MS Visual Basic 6
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37. Do Until...Loop Structure
Do Until condition
statements
Loop
Where
The condition is tested, and if false the loop is repeated. When the condition is true, the loop statements are skipped the statement after Loop is executed.
Exploring MS Visual Basic 6
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38. Do Until...Loop Structure
‘Calculate the factorial of a number given by user
Dim Factorial As Double
Dim I As Integer
I = 1
Factorial = 1
Do While I <= Val (txtAnswer.text)
Factorial = Factorial + 1
I = I + 1
Loop
User gives number
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39. Loops with the Marching Band Project
Hands-On Exercise 3
Create the Marching Band Project
Add Command Buttons and a Timer
Add Controls to Display the Band
Add Banner Comments
Add Code for Buttons and the Form
Add Code to Add Animation
Run, Save, Test and Debug Your Project
Create a Copy of the Project
Change Animation Code
Update, Run, Save, Test and Debug
Exit Visual Basic
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Summary ...
Fundamental programming demonstrated
Variables vs. Constants
Data types
Local vs Global variables
Functions and Procedures
Control structures: sequence, selection and repetition
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Summary
Statements
Dim, Static, Const
Public, Private
Sub, Function
Do...Loop, Do While...Loop, Do Until...Loop
For Each...Next, For...Next
If...Then...Else
Select Case
Exploring MS Visual Basic 6
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42. Practice with Visual Basic
1. Learning to Subtract Game
2. Wind Chill in Celsius
3. Heat Index
4. Rock, Paper, Scissors Game
5. Creating Variables
6. Event-driven Programming
7. For...Next Loop
8. Digital Clock
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Case Studies
Calculate a Formula
Weather Calculations
More Fun and Games
More Web Resources for Visual Basic
Exploring MS Visual Basic 6
Copyright 1999 Prentice-Hall, Inc.