1. Fundamentals of Programming in Visual Basic
Chapter 3
Fundamentals of Programming in Visual Basic
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2. Chapter 3 - Visual Basic Schneider
Outline and Objective
Visual Basic Objects
Visual Basic Events
Numbers
Strings
Input/Output
Built-In Functions
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3. The initial Visual Basic screen
Menu bar
Toolbar
Project
Explorer
window
Toolbox
Properties
window
Form
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4. Steps to Create a Visual Basic Program
1. Create the Objects
2. Set Properties
3. Write the Code for each Event
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5. Four most useful Visual Basic Controls
Text Boxes
Labels
Command Buttons
Picture Boxes
The icons in the Tool Box represent objects that can be placed on the form.
The four objects discussed today are: text boxes…..
Text Box: you use a text box primarily to get information, referred to as input , from the user
Label is placed next to text box to tell the user what type of information to enter into the to he text box
Command button : The user clicks a command button to initiate an action
Picture Boxes: You use a picture box to display text or graphics
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6. 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
Go over resizing and dragging the text box
The first line of the properties window (called the object box) reads “Text1 TextBox” . Text1 is the current name of the textbox.
The two Tab permit you to view the list of properties either alphabetically or grouped by categories..
We discuss four properties :
The Text property determines the words in the text box.
Press Shift+Ctrl+F to move to the first property beginning with
F . Move to the property ForeColor. The foregroung color is the
color of the text.. Click on Palette tab to display a selection of colors.
Highlight the Font property and change it to Italic
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7. Chapter 3 - Visual Basic Schneider
A Text Box Walkthrough
Text box
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8. Some Useful Properties:
Name
Caption
Border style
Visible
Back Color
Alignment
Font
Border Style: Setting the BorderStyle to 0-None removes the border from an object
Visible: Setting the property to false hides an object when the program run. The object can be set to reappear with code
BackColor: Specifies the background color for text box, label, picture box or form.. Also specific background color for a command button having Style set to “1-Graphical”
BackStyle: The background of a label is opaque by default. Setting the background style of a label to transparent causes whatever is behind the label remain visible.; the background color of the label essentially becomes “see through”
Font: Two unusual fonts are Symbols and Wingdings> For instance with the windingsfonts , changing the text to % & ‘ and J yields a bell, a book, a candle and a smiling face
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9. Chapter 3 - Visual Basic Schneider
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.
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10. Chapter 3 - Visual Basic Schneider
Naming Objects:
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11. Chapter 3 - Visual Basic Schneider
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”.
When a VB program is run, a form and its controls appear on the screen. Normally, nothing happens until the user takes an action, such as clicking a control or pressing the Tab key.
Such an action is called event.
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12. The steps for creating a VB program:
Create the Interface.
Set Properties for the objects.
Write the code that executes when event occur.
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13. 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.
Object Property Setting
frmWalkthrough Caption Demonstration
txtPhrase Text (blank)
cmdBold Caption Make Phrase Bold
Object Box
Procedure Box: Contains a list of all possible event procedures associated with the text box
Choose txtPhrase_LostFocus()
txtPhrase.Font.Size = 12
End Sub
Choose GotFocus and type: txtPhrase.Font.Size = 8
txtPhrase.Font.Bold = False
Go to command Button and choose cmdBold_Click and type txtPhrase.Font.Bold = True
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14. Chapter 3 - Visual Basic Schneider
Example of An Event
Private Sub objectName_event ( )
statements
End Sub
Private Sub txtOne_GotFocus( )
txtOne.Font.Size = 12
txtOne.Font.Bold = False
The word Sub signals the beginning of the event procedure, and also identifies the Object and the event occurring to that object
The word private indicates that the event procedure cannot be invoked by an event from another procedure.
The word Sub means subprogram
Example: the event procedure
private Sub cmdButton_Click ()
txtBox.Text = “”
End Sub
The event clicking cmdButton is different from the event clicking picBox_Click
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15. Chapter 3 - Visual Basic Schneider
More Example
Private Sub cmdButton_Click( )
txtBox.ForeColor = vbRed
txtBox.Font.Size = 24
txtBox.Text = “Hello”
End Sub
Each color can be identified by a sequence of digits and letter beginning with &H. &HFF& = Red
&HFF00& = Green
&HFF000& = Blue
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16. Components of Visual BASIC Statements
Variables
Keywords (reserved words)
Constants
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17. Chapter 3 - Visual Basic Schneider
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
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18. 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.
VB does not distinguish between uppercase and lowercase letters
Example: numberOfCars, tax_Rate_1994
Let statement assigns values to variables and Print method displays the values of variable
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19. Chapter 3 - Visual Basic Schneider
Numeric Variables
Used to store Numbers .
The value is assigned either by the programmer or by calculation.
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20. Valid Numeric Variable Names:
timeElapsed
taxRate
speed n
celsius
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21. Invalid Numeric Variable Names:
maximum/average
1stChoice
square yard
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22. Chapter 3 - Visual Basic Schneider
Constant
Similar to a variable, but can NOT change during the execution of a program.
Types of Constants:
numeric constants
string constants
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23. Valid Numeric Constants:
Integer Real number
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24. Invalid Numeric Constants:
14, %
$190.04
&
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25. Numeric Constants in a Statement:
tax = 0.02 * (income * dependence)
sum = 2 + x y
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26. Chapter 3 - Visual Basic Schneider
String Constants:
A group of alphanumeric data consisting of any type of symbols.
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27. Valid String Constants
“A rose by any other name”
“Down By the Sea Shore”
“134.23”
“She said, ‘stop , thief!’”
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28. Invalid String Constants
‘Down by the Seashore’
“134.24
“She said, “Stop, thief!””
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29. Arithmetic Operations & Hierarchy of Operations
Operator operation Basic expression
^ Exponentiation A ^ B
* Multiplication A * B
/ Division A / B
Addition A + B
Subtraction A - B
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30. Chapter 3 - Visual Basic Schneider
Examples
Evaluate the following expressions:
x = 3 * / 3
x = 4 ^ (8 / 4)
y = / (3 * (10 - 9))
z = ^ 2
m = 6 / 3 + 3
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31. Chapter 3 - Visual Basic Schneider
Keywords
Words that have predefined meaning to Visual Basic .
Can Not be used as variable names.
Example: Print
Cls If
While
The VB editor automatically capitalizes the first letter of reserved word
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32. 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 .
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33. 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
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34. Example of Print Statement
picOutput.Print speed
picOutput.Print taxRate
picOutput.Print “Class average is”; total / 3
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35. Chapter 3 - Visual Basic Schneider
Example
x = 15
y = 5
picOutput.Print (x + y) / 2, x / y
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36. Chapter 3 - Visual Basic Schneider
Output
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37. 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.
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38. 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.
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39. Chapter 3 - Visual Basic Schneider
Example
Private Sub cmdCompute_Click( )
picResults.Cls
a = 5
b = 4
c = a * (2 + b)
picResults.Print c
End Sub
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40. Valid Assignment Statement
count = count + 1
num = 5
count = count + num /2
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41. Chapter 3 - Visual Basic Schneider
Invalid Assignments
10 = count
count + 1 = count
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42. Chapter 3 - Visual Basic Schneider
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).
The value of string variable is assigned or altered with Let statements and displayed with Print methods just like the
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43. 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
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44. Chapter 3 - Visual Basic Schneider
Concatenation
Two string can be combined with the concatenation operation.
Concatenation is represented with the ampersand ( & ) sign.
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45. Example of Concatenation:
strVar1 = “Hello”
strVar2 = “World”
picOutput.Print strVar1& strVar2
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46. Example of Concatenation
txtBox.Text = “32” & CHR(176) & “ Fahrenheit”
Displays 32 Fahrenheit in the text box
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47. Chapter 3 - Visual Basic Schneider
Data Types
Each variable in the program is assigned to a data type.
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48. 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
From now on we will declare all variables. Declaring variables is regarded as good programming practice.
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49. Chapter 3 - Visual Basic Schneider
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
The default data type is a single precision numeric variable
Therefore Number and Number! Are the same
Double precision variable is used to store number with many digits
A single precision variable is accurate to about seven decimal points where double precision is accurate to about 15 decimal points
Is used when a high degree of accuracy is needed.
If you try to assign a real number , the number would be cut off and an integer would be assigned to it.
Declaring variables is regarded as good programming practice
Example: Dim variableName As String
Dim variableName As Single
Type Declaration Tags
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50. 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.
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51. 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)
Function Input Output
Str number string
Val string number
If str is a string representation of a number, then Val(str) is that number. Conversely, if num is a number, then Str(num) is a string representation of the number.
Therefore statements such as
numVar = Val(txtBox.Text)
and
txtBox.Text = Str(numVar)
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52. 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))
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53. 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
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54. 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 .
1. The name of the file: follows the same rules for naming program files.
Use invest.bas and invest.dat
2. The mode in which the file is to be used , can be output, input, append .
Output: indicates data is written to the file from the program
input: the contents of the file are being read into the program
append :allows new records to be added to an existing file.
A butter is a reserved part of the primary storage unit used a s temporary storage area for the data that is being written or read from a file
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55. Example of Reading from a File:
Open the file
Open “DATA.TXT” for Input As #1
Input #1, num1
Input #1, num2
picOutput.Print num1+num2
Close #1
Reference number
Read from the file
Read the data and assign it to num1
A file can have either one item per line or many items (separated by commas) can be listed on the same line
the items of data will be assigned to variables one at the time in the order they appear in the file.
1. Choose a number from 1 to 255 to be the reference number for the file
2. Open the file for input
3. Read items of data in order, one at the time, from the file with Input sattement
Show Examples: Path is C;\F98 CSE181\Examples\Ch3\Data.txt
The response typed into an input box is treated as a single string value, no matter what is typed. Quotation marks are not needed, and if included, are considered as part of the string.
Numeric data typed into n input box should be converted to a number with Val before it is assigned to a numeric variable or used in calculation.
Close the file
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56. Example of Reading from a File:
Open “Data.txt” for Input As #1
Input #1,num1, num2
picOutput.Print num1+num2
Close #1
Example #1: create a file named Student.dat
Prepare the file to receive data
If a file already exists, it is destroyed and a new file is created.
Associated with the file Student.date with buffer #1. As long as the file is open. Buffer #1 is used temporarily before the data is written to the file on disk
Other statement in the program use this number to identify the file..
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57. 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.
After users types in a response into the rectangle at the bottom of the screen and press Enter, the response is assigned to the string variable.
Normally, text box is used to obtain input, sometimes we want just one piece of input and would rather not have a text box and label stay on the screen for ever.
Example
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58. Chapter 3 - Visual Basic Schneider
Syntax for an Input Box
stringVar = InputBox (prompt, title)
Where the prompt is the message you want displayed inside the dialog box, and title is the text you want displayed in the dialog box’s title bar.
Both the prompt and the tittle must be enclosed in quotation marks.
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59. Chapter 3 - Visual Basic Schneider
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 input
box would pop up
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60. Using Message Box for Output:
Use message box to get the user’s attention.
Message box is a predefined dialog box too.
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61. Chapter 3 - Visual Basic Schneider
Syntax for Message Box
MsgBox prompt, , title
When a statement of the form above is executed , where prompt and title are strings, message box with prompt displayed and the title bar caption title appears., and stays on the screen until the user presses Enter or clicks K.
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62. Chapter 3 - Visual Basic Schneider
Example of Message Box
MsgBox “Nice try, but no cigar”, , “Consolation”
Stays on the
screen until the
user presses OK
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63. Formatting the Output:
Create user friendly output.
In the Print method, control of the spacing of the output is controlled by the following devices.
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64. Formatting the Output:
Semicolon
Comma
Tab Function
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65. Chapter 3 - Visual Basic Schneider
Semicolons
The next value output is placed in the next column position.
Example:
picOutput.Print “Patrick”; ”Jon”
Output Screen:
PatrickJon
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66. Chapter 3 - Visual Basic Schneider
Example of Semicolon
picOutput.Print “Patrick”; ” Jon”
Output Screen:
Patrick Jon
Space here
Space here
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67. Chapter 3 - Visual Basic Schneider
Example of Semicolon
picOutput.Print 100; -200; 300
Output Screen:
Two spaces
One space
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68. Chapter 3 - Visual Basic Schneider
Commas
The next value output is placed in the next available print zone.
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69. Chapter 3 - Visual Basic Schneider
Print Zones
Each print zone is 14 positions wide.
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70. Chapter 3 - Visual Basic Schneider
Example of Print Zone
Example:
picOutput.Print “SEE”, ”YOU”, ”SOON”
Output Screen:
SEE YOU SOON
See in column 1 Y in column 15 and S in column 29
Column 29
Column 15
Column 1
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71. Chapter 3 - Visual Basic Schneider
Example of Commas
A print zone can be skipped by typing consecutive commas
Example:
picOutput.Print “HOURLY”, , “PAY”
Output Screen:
HOURLY PAY
Example 3.5.5
Column 29
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72. Chapter 3 - Visual Basic Schneider
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.
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73. Example of Tab Function
picOutput.Print Tab(3); “Hi there!” ;TAB(25) ;“Bye!”
Output Screen:
Hi there! Bye!
Example 3.5.6
Organizes data into columns of a table
Column 25
Column 3
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74. Chapter 3 - Visual Basic Schneider
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
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75. Chapter 3 - Visual Basic Schneider
Functions:
What is a function?
What are advantages of using functions?
How do you use a function?
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76. Chapter 3 - Visual Basic Schneider
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.
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77. Chapter 3 - Visual Basic Schneider
Types of Functions
Built-In functions (library)
User-defined functions
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78. Chapter 3 - Visual Basic Schneider
Example
x = Sqr(225)
y = Int (2.7)
str1 = Left (“John Smith”, 4)
number = Rnd
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79. Types of Standard Functions
Numeric Functions (manipulate numbers)
String Functions (manipulate strings)
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80. Chapter 3 - Visual Basic Schneider
Numeric Functions
Example for Int function and Sqr function
Example : rounds a positive number to the nearest integer..
To round a number t two decimal places
r = Int (100*n + 0.5) / 100
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81. 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
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82. Commonly-Used String Functions
Function: Left (“Penguin”,4)
Purpose: Returns the number of specified characters, starting at the beginning of the string.
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83. Commonly-Used String Functions
Function: Right (“Gotham City” , 4)
Purpose: Returns the number of specified characters from the end of the string .
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84. Commonly-Used String Functions
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.
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85. Commonly-Used String Functions
Function: UCase (“Yes”)
Purpose: Converts any lowercase letters in string to uppercase.
Go over Example 6 page 121
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86. 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.
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87. String-Related Numeric Function
Function: Len (“John Smith”)
Purpose: Returns the number of characters in the string.
Is 10
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88. Chapter 3 - Visual Basic Schneider
Format Function
The format functions provide detailed control of how numbers, dates, and strings are displayed.
Numbers can be made to line up uniformly and be displayed with dollar signs, commas and a specified number of decimal places. Dates can be converted
to a long or medium form. Strings can be right justified.
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89. Examples of Format Functions
FormatNumber ( , 1) ,345.6
FormatCurrency ( , 2) $12,345.68
FormatPercent (.185, 2) %
FormatNumber (1 + Sqr(2), 3)
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90. Chapter 3 - Visual Basic Schneider
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 symbols.
If num is number , numeric expression , or a string representation of a number, and fmt is a s string of symbols, then Format (num,fmt) is asserting of character with the number right justified in a field of n spaces.
If num is any string,produced by a Format function , then the value of Format (num,fmt) contains the string right-justified in a field of n spaces.
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91. Chapter 3 - Visual Basic Schneider
Examples:
Format (12345,
Format (123,
Format (“123.4”,
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92. Chapter 3 - Visual Basic Schneider
Example
FormatDateTime (“ ”, vbLongDate)
Output: Wednesday, September 15, 1999
String Value:
Sunday, September20, 1998
09-Sep-98
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93. Chapter 3 - Visual Basic Schneider
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
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94. 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?
Int(100* Rnd) + 1
@ * Rnd + 2
(Int (50 * Rnd) + 1) *2
Int( 2* Rnd)
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