Chapter 3 - Visual Basic Schneider Chapter 3 Fundamentals of Programming in Visual Basic.

Chapter 3 - Visual Basic Schneider

Chapter 3

Fundamentals of Programming in Visual Basic


Outline and Objective

• Visual Basic Objects• Visual Basic Events

• Numbers• Strings• Input/Output• Built-In Functions


The initial Visual Basic screen

Toolbox

Project Explorerwindow

Properties window

Form

ToolbarMenu bar


Steps to Create a Visual Basic Program

1. Create the Objects

2. Set Properties

3. Write the Code for each Event


Four most useful Visual Basic Controls

• Text Boxes

• Labels

• Command Buttons

• Picture Boxes


A Text Box Walkthrough:

• Double-click on Text Box to add a Text Box to your form

• Activate the Properties window (Press F4)

• Set values of Properties for Text Box


A Text Box Walkthrough

Text box


Some Useful Properties:

• Name

• Caption

• Border style• Visible• Back Color• Alignment• Font


Naming Objects:

• Use the Property window to change the Name property of an object

• Good Programming habit is that each name begins with three letter prefix that identifies the type of control.


Naming Objects:Object Prefix Example

Command Button cmd cmdStart

Form frm frmPayroll

Label lbl lblName

Picture box pic picClouds

Text box txt txtAddress


Visual Basic Events

• Code is a set of statements that will be executed when you run a program.

• Write Code for each Event.

• Most Events are associated with Objects.

• The code for each event is called an “Event Procedure”.


The steps for creating a VB program:

• Create the Interface.

• Set Properties for the objects.

• Write the code that executes when event occur.


An Event Procedure Walkthrough

• Create the interface.

• Set Properties.

• Double click on the object to open the Code window.

• Click on the Procedure box to find the event

• Write the code for that event.


Example of An Event

Private Sub objectName_event ( )

statements

End Sub

Private Sub txtOne_GotFocus( )

txtOne.Font.Size = 12

txtOne.Font.Bold = False

End Sub


More Example

Private Sub cmdButton_Click( )

txtBox.ForeColor = vbRed

txtBox.Font.Size = 24

txtBox.Text = “Hello”

End Sub


Components of Visual BASIC Statements

• Variables

• Keywords (reserved words)

• Constants


Variables

• A storage location in main memory whose value can change during program execution.

• These storage locations can be referred to by their names.

• Every variable has three properties: a Name, a Value, and a Data Type.

• Types of variables: Numeric and String


Rules for Creating Variable Names

• Must begin with a letter.

• Can contain letters, numeric digits.

• Can have up to 255 characters.

• Can Not be restricted keyword.


Numeric Variables

• Used to store Numbers .

• The value is assigned either by the programmer or by calculation.


Valid Numeric Variable Names:

timeElapsed

taxRate

speed

n

celsius


Invalid Numeric Variable Names:

• maximum/average

• 1stChoice

• square yard


Constant

• Similar to a variable, but can NOT change during the execution of a program.

• Types of Constants:– numeric constants– string constants


Valid Numeric Constants:

Integer Real number

-2987 -1900.05

+16 0.0185

5 10.56


Invalid Numeric Constants:

14,005.5 6.8%

33- $190.04

15 78 3.5&


Numeric Constants in a Statement:

tax = 0.02 * (income - 500 * dependence)

sum = 2 + x + 4.6 + y


String Constants:

• A group of alphanumeric data consisting of any type of symbols.


Valid String Constants

“A rose by any other name”

“Down By the Sea Shore”

“134.23”

“She said, ‘stop , thief!’”


Invalid String Constants

‘Down by the Seashore’

“134.24

“She said, “Stop, thief!””


Arithmetic Operations & Hierarchy of Operations

Operator operation Basic expression

^ Exponentiation A ^ B

* Multiplication A * B

/ Division A / B

+ Addition A + B

- Subtraction A - B


Examples

Evaluate the following expressions:

x = 3 * 6 - 12 / 3

x = 4 ^ (8 / 4)

y = 12 + 6 / (3 * (10 - 9))

z = 5 + 4 ^ 2

m = 6 / 3 + 3


Keywords

• Words that have predefined meaning to Visual Basic .

• Can Not be used as variable names.

Example: Print

Cls

If

While


Visual Basic Print Statement

• Print: Is a method used to display data on the screen or printer.

• Can be used to print value of variables.

• Can be used to print value of arithmetic expressions .


Example of Print Statements

Private Sub cmdCompute_Click()

picResults.Print 3 - 2

picResults.Print 3 * 2

picResults.Print 3 / 2

picResults.Print 3 ^ 2

picResults.Print 2 * (3 + 4)

End Sub


Example of Print Statement

• picOutput.Print speed

• picOutput.Print taxRate

• picOutput.Print “Class average is”; total / 3


Example

x = 15

y = 5

picOutput.Print (x + y) / 2, x / y


Output

10 3


Internal Documentation

• An apostrophe (‘) can be used to indicate comments; comments are ignored by Visual Basic.

• The keyword Rem can also be used instead of an apostrophe for comments.

• Remarks can also be placed after program statement too.


Visual Basic Assignment Statement

• The statement var = expr assigns the value of the expression to the variable.

• Assigns the value of the expression on the right to the variable on the left.


Example

Private Sub cmdCompute_Click( )picResults.Cls

a = 5

b = 4

c = a * (2 + b)

picResults.Print c

End Sub


Valid Assignment Statement

count = count + 1

num = 5

count = count + num /2


Invalid Assignments

10 = count

count + 1 = count


String Variables

• A String variable stores character strings.

• The rules for naming string variables are identical to those of numeric variables.

• When a String variable is first declared, its value is the null string. (that is, the empty string).


Example of String Variable

Private Sub cmdShow_Click()

picOutput.Cls

phrase = "win or lose that counts."

picOutput.Print "It's not whether you "; phrase

picOutput.Print "It's whether I "; phrase

End Sub


Concatenation

• Two string can be combined with the concatenation operation.

• Concatenation is represented with the ampersand ( & ) sign.


Example of Concatenation:

strVar1 = “Hello”

strVar2 = “World”

picOutput.Print strVar1& strVar2


Example of Concatenation

txtBox.Text = “32” & CHR(176) & “ Fahrenheit”


Data Types

• Each variable in the program is assigned to a data type.


Declaring Variable Types

• Use the Dim statement to Declare the type of a variable.

Example:

Dim number As Integer

Dim flower As String

Dim interestRate As Single


Data Types :

• Single-precision numeric variable: Stores real numbers

• Double-precision numeric variable: Stores real numbers with many digits

• Integer: Stores integers

• Long integer: Stores integers with many digits


Using Text Boxes for Input/Output

• The contents of a text box are always a string.

• Numbers are also stored in text boxes as strings.


Using Text Boxes for Input/Output

• Therefore, the contents of a text box should be changed to a number before being assigned to a numeric variable.

• Val (txtBox.Text) changes the input string into a number.

Example:

numVar = Val (txtBox.Text)


Example (convert miles to furlong and vice versa)

Private Sub txtFurlong_LostFocus()

txtMile.Text = Str(Val(txtFurlong.Text / 8))

End Sub

Private Sub txtMile_LostFocus()

txtFurlong.Text = Str(8 * Val(txtMile.Text))

End Sub


The KeyPress Event Procedure

Private Sub txtCharacter_KeyPress(KeyAscii As Integer)

txtCharacter.Text = ""

picOutput.Cls

picOutput.Print Chr(KeyAscii); " has ANSI value"; KeyAscii

End Sub


Reading Data from Files

1. Choose a number to be the reference number to the file.

2. Set the mode in which the file is to be used:

– Input

– Output

– Append

3. Read the data sequentially using Input statement.

4. Close the file .


Example of Reading from a File:

Open “DATA.TXT” for Input As #1

Input #1, num1

Input #1, num2

picOutput.Print num1+num2

Close #1

Reference number

Read the data and assign it to num1

Open the file

Read from the file

Close the file


Example of Reading from a File:

Open “Data.txt” for Input As #1

Input #1,num1, num2

picOutput.Print num1+num2

Close #1


Input from an Input Box:

• Use Text Box to obtain input.

• For one piece of input use input box instead of a text box

• Input Box is a predefined dialog box.


Syntax for an Input Box

stringVar = InputBox (prompt, title)


Example of Input Box

Private Sub cmdDisplay_Click()

Dim fileName As String, prompt As String, title As String

Dim houseNumber As Single, street As String

prompt = "Enter the name of the file containing the information."

title = "Name of File"

fileName = InputBox(prompt, title)

Open fileName For Input As #1

Input #1, houseNumber

Input #1, street

picAddress.Print "The White House is at"; houseNumber; street

Close #1

End Sub

After executing an inputbox would pop up


Using Message Box for Output:

• Use message box to get the user’s attention.

• Message box is a predefined dialog box too.


Syntax for Message Box

• MsgBox prompt, , title


Example of Message Box

MsgBox “Nice try, but no cigar”, , “Consolation”

Stays on thescreen until the user presses OK


Formatting the Output:

• Create user friendly output.

• In the Print method, control of the spacing of the output is controlled by the following devices.


Formatting the Output:

• Semicolon

• Comma

• Tab Function


Semicolons

• The next value output is placed in the next column position.

Example:

picOutput.Print “Patrick”; ”Jon”

Output Screen:

PatrickJon


Example of Semicolon

picOutput.Print “Patrick”; ” Jon”

Output Screen:

Patrick Jon

Space here

Space here


Example of Semicolon

picOutput.Print 100; -200; 300

Output Screen:

100 -200 300

One space

Two spaces


Commas

• The next value output is placed in the next available print zone.


Print Zones

• Each print zone is 14 positions wide.


Example of Print Zone

Example:

picOutput.Print “SEE”, ”YOU”, ”SOON”

Output Screen:

SEE YOU SOON

Column 1

Column 15

Column 29


Example of Commas

• A print zone can be skipped by typing consecutive commas

Example:

picOutput.Print “HOURLY”, , “PAY”

Output Screen:

HOURLY PAYColumn 29


Tab Function

• Starts output in the specified column.

• It provides more flexibility in formatting.

• Only use Semicolons with the Tab function.

• Only can be used to advance the print position.


Example of Tab Function

Example: picOutput.Print Tab(3); “Hi there!” ;TAB(25) ;“Bye!”

Output Screen:

Hi there! Bye!

Column 3

Column 25


Example of Tab

Example:

picOutput.Print TAB(25); 5; TAB(15); 4; TAB(5); 3

Output Screen:

5

4

3

Column 25

Column 15

Column 5


Functions:

• What is a function?

• What are advantages of using functions?

• How do you use a function?


What is a function

• A sub program designed to perform a specific task.

• A sub program designed to return a single value to the calling program.


Types of Functions

• Built-In functions (library)

• User-defined functions


Example

• x = Sqr(225)

• y = Int (2.7)

• str1 = Left (“John Smith”, 4)

• number = Rnd


Types of Standard Functions

• Numeric Functions (manipulate numbers)

• String Functions (manipulate strings)


Numeric Functions

Rnd Returns a number between 0 and 1.(excluding 1)

Sqr(n) Returns the square root of a number.

Round(n,r) The number n is rounded to r decimalplaces.

Int(n) Returns the largest integer less thanor equal to a number


Example of Numeric Functions

Private Sub cmdEvaluate_Click()

Dim n As Single, root As Single

picResults.Cls

n = 6.76

root = Sqr(n)

picResults.Print root; Int(n); Round(n,1)

End Sub


Commonly-Used String Functions

Function: Left (“Penguin”,4)

Purpose: Returns the number of specified characters, starting at the beginning of the string.



Function: Right (“Gotham City” , 4)

Purpose: Returns the number of specified characters from the end of the string .



Function: Mid (“Commissioner” , 4, 3)

Purpose: Returns the character string starting at the position indicated by the first number and continuing for the length specified by the second number.



Function: UCase (“Yes”)

Purpose: Converts any lowercase letters in string to uppercase.


String-Related Numeric Functions

Function: InStr (“John Smith”, ” “)

Purpose: Searches for the first occurrence of one string in another and gives the position at which the string is found.


String-Related Numeric Function

Function: Len (“John Smith”)

Purpose: Returns the number of characters in the string.


Format Function

The format functions provide detailed control of how numbers, dates, and strings are displayed.


Examples of Format Functions

FormatNumber (12345.678, 1) 12,345.6

FormatCurrency (12345.678, 2) $12,345.68

FormatPercent (.185, 2) 18.50%

FormatNumber (1 + Sqr(2), 3) 2.414


Format Function

• Format (expr, “@……..@”)

Purpose: The value of this function contains the string right justified in a field of n spaces. Where n is a string of n @ symbols.


Examples:

Format (12345, “@@@@@”) 12345

Format (123, “@@@@@”) 123

Format (“123.4”, “@@@@@”) 123.4


Example

FormatDateTime (“9-15-99”, vbLongDate)

Output: Wednesday, September 15, 1999


Rnd Function

• Returns a random number from 0 up to 1.

(excluding 1).

Example: Displays a random integer from 1 through 6.

picBox.Print Int(6 * Rnd) + 1


Examples of Using Rnd Function:

An integer from 1 through 100?

A number from 2 through 4 (excluding 4)?

An even integer from 2 through 100 ?

Either 0 or 1?

Chapter 3 - Visual Basic Schneider Chapter 3 Fundamentals of Programming in Visual Basic.

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Transcript of Chapter 3 - Visual Basic Schneider Chapter 3 Fundamentals of Programming in Visual Basic.