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

Chapter 3Programming Fundamentals

Writing Code

3

Exploring Microsoft Visual Basic 6.0Copyright © 1999 Prentice-Hall, Inc.

By Carlotta Eaton

Exploring MS Visual Basic 6

Copyright 1999 Prentice-Hall, Inc. 2

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



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



Modules and Procedures

Code - the man behind the curtainModules - large units of code that

comprise a Visual Basic applicationForm Modules - contains a form

and code for the formStandard Modules - contains code

that is typically used by other modules



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



The Code Editor Window

View and edit code Views

Full Module View Procedure View

Features Auto List Members Auto Quick Info Auto Syntax Check



The Code Editor WindowObject List Box

Procedure List Box

Auto List Members

Full Module View button



The Code Editor Window

Help window

Error message box

Syntax error in Red

Procedure view button



Syntax Boxes

Syntax for a Visual Basic statement is shown in a syntax box

Reserved words are shown in boldProgrammer named words are shown in

italicsSee next slide for an example



The Sub Statement

Private Sub controlname_eventname( )

Statements

End SubWhere

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



The Sub Statement

ExamplePrivate Sub cmdCalcTriangle_Click

Dim Base As Single

Dim Height As Single

Dim Height As Single

Area = 1 / 2 * (Base * Height)

End Sub



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



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)



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



Declaring Variables

Declare variables using the Dim or Static statementsDim statement - value of variable

preserved only until procedure endsStatic statement - value of variable

preserved the entire time the application is running



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



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



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 = 5FirstName = “Steve”LoanAmount = 67.38Length = 17.8

Note: Order is important. Variable name always on the left, and value on the right.



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 3.14159265358979Const MaxNumber As Integer = 100



The Wind Chill Project

Write a program that calculates the wind chill temperature

Find a formula - UST Today Weather Web site www.usatoday.com/weather/wchilform.htm

Inputs: Wind Speed and TemperatureOutputs: Wind Chill Temperature



The Wind Chill Project

Orginal formula WC = 0.0817(3.71(V **0.5) + 5.81 -

0.25V)(T - 91.4) + 91.4Visual Basic statement

WC = 0.0817 * (3.71 * Sqr(V) + 5.81 -(0.25 * V)) * (T - 91.4) + 91.4



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



Functions

Locating built-in functions Open the Functions online reference

book or search for a function by nameProgrammer-written functions

Write your own functions using the Function statement



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



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 = 0.0817 * (3.71 * Sqr(V) _

+5.81 - (0.25*V)) * (T-91.4)+91.4

End Function



WindChill Function

Private Sub cmdCalculate_Click()

WC = WindChill()

txtWindChill.Text = Cint(WC)

End Sub

When the cmdCalculate button is clicked, the WindChill function is executed



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



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



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



Learning to Add Game

Reward for correct answer



Learning to Add Game

Image for incorrect answer



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



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



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



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.



Do While...Loop Structure

Do While condition

statements

Loop

Where

The condition is tested, and if true the loop isrepeated. When the condition is false, the loopstatements are skipped the statement after Loopis executed.



Do Until...Loop Structure

Do Until condition

statements

Loop

Where

The condition is tested, and if false the loop isrepeated. When the condition is true, the loopstatements are skipped the statement after Loopis executed.



‘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

Do Until...Loop Structure

User gives

number



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



Summary ...

Fundamental programming demonstrated

Variables vs. ConstantsData types Local vs Global variablesFunctions and ProceduresControl structures: sequence, selection

and repetition



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



Practice with Visual Basic

1. Learning to Subtract Game2. Wind Chill in Celsius3. Heat Index4. Rock, Paper, Scissors Game5. Creating Variables6. Event-driven Programming7. For...Next Loop8. Digital Clock



Case Studies

Calculate a FormulaWeather CalculationsMore Fun and GamesMore Web Resources for Visual

Basic

Documents

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