1. Fundamentals of Programming in VB.NET
Chapter 3
Fundamentals of Programming in VB.NET
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2. Fundamentals of Programming in VB.Net
VB.NET Controls
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3. Fundamentals of Programming in VB.Net
Add an "access key"
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4. Fundamentals of Programming in VB.Net
The Name Property
How the programmer refers to a control in code
Name must begin with a letter
Must be less than 215 characters long
May include numbers and the underscore
Use appropriate 3 character naming prefix
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5. Fundamentals of Programming in VB.Net
Control Name Prefixes
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6. Fundamentals of Programming in VB.Net
VB.Net Events
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7. Fundamentals of Programming in VB.Net
VB.NET Events
An Event Procedure Walkthrough
Properties and Event Procedures of the Form
The Declaration Statement of an Event Procedure
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8. Fundamentals of Programming in VB.Net
What is an event?
An event is an action, such as the user clicking on a button
Usually, nothing happens until the user does something and generates an event
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9. Fundamentals of Programming in VB.Net
VB.NET program:
Create the interface; that is, generate, position, and size the objects.
Set properties; that is, configure the appearance of the objects.
Write the code that executes when events occur. This block of code is called event procedure.
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10. Fundamentals of Programming in VB.Net
Event Procedures
Private Sub objectName_event(
ByVal sender As System.Object,
ByVal e As System.EventArgs)
Handles objectName.event
statements
End Sub
Private Sub ObjectName_event(…) Handles objectName.event
Because the book does not make use of the parameter list, it is replaced with an ellipsis
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11. Fundamentals of Programming in VB.Net
Statements
Properties of controls can be changed both in the Properties window and in the statements of the event procedure.
The statement we use to change the property value is call an Assignment statement
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12. Fundamentals of Programming in VB.Net
Changing Properties
Properties are changed in code with the following:
controlName.property = setting
This is an assignment statement
txtBox.ForeColor = Color.Red
Me.Text = "Demonstration“
Instead of
(VB.6) Form1.Text = "Demonstration"
The form is referred to by the keyword Me.
The setting value on the right hand side of the equal sign is being assigned to the property of the control listed on the left hand side of the equal sign
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13. Fundamentals of Programming in VB.Net
Program Region
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14. Dropdown Boxes Automatically pops up to give the programmer help.
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15. Fundamentals of Programming in VB.Net
Help
Help menu
Press ALT/H/I - Help index window
Dynamic help – samples
(Member Listing)
Type dot “.” following a word
Type parenthesis following a word
Context-sensitive help
Place cursor on the word, and press F1
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16. Fundamentals of Programming in VB.Net
Event Outcomes
Private Sub txtFirst_TextChanged(...)
Handles txtFirst.TextChanged
txtFirst.ForeColor = Color.Blue
End Sub
Private Sub btnRed_Click(...)
Handles btnRed.Click
txtFirst.ForeColor = Color.Red
Private Sub txtFirst_Leave(...)
Handles txtFirst.Leave
txtFirst.ForeColor = Color.Black
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17. The Declaration Statement of an Event Procedure
A declaration statement for an event procedure:
Private Sub btnOne_Click(...)
Handles btnOne.Click
The name can be changed at will.
Private Sub ButtonPushed(...)
Handling more than one event:
Handles btnOne.Click, btnTwo.Click
btnOne_Click is the name of the event procedure, and btnOne.Click identifies the
event that triggers the procedure
Also, an event procedure can be triggered by more than one event.
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18. Fundamentals of Programming in VB.Net
Numbers
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19. Fundamentals of Programming in VB.Net
Numbers
Integer and Float Point Number
Arithmetic Operations
Variables
Built-In Functions:
Math.Sqrt
Int
Math.Round
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20. Arithmetic Operations
Numbers are called numeric literals
Five arithmetic operations in VB.NET
+ addition
- subtraction
* multiplication * 2
/ division / 2
^ exponentiation ^ 2
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21. Parentheses of Arithmetic operation
Order of Operation:
() Inner to outer,left to right
^ Left to right in expression
* / Left to right in expression
+ - Left to right in expression
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22. Fundamentals of Programming in VB.Net
Scientific Notation
Scientific notation represents a number by using power of 10 to stand for zeros
In VB.Net
b • 10 r is written as bEr
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23. Fundamentals of Programming in VB.Net
Scientific Notation
r is a two digit number preceded by plus sign if r is positive and by a minus sign if r is negative
10 • 10 – ^ E-20
1.2 • * 10 ^ E+03
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24. Fundamentals of Programming in VB.Net
Variables
A variable is a name that is used to refer to an item of data. The value assigned to the variable may change.
Up to 16,838 characters long
Begin with a letter or an underscore
Consist of only letters,digits and underscores
A Variable name is written in lowercase letters except for the first letters of additional words, such as costOfIT201.
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25. Fundamentals of Programming in VB.Net
Variables
Declaration:
Dim speed As Double
Data type
Variable name
Assignment:
speed = 50
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26. Variable Initialization
Numeric variables are automatically initialized to 0:
Dim varName As Double
To specify a nonzero initial value
Dim varName As Double = 50
declares a variable named varName to be of type Double. Actually, the Dim statement
causes the computer to set aside a location in memory with the name varName. Since
varName is a numeric variable, the Dim statement also places the number zero in that
memory location. (We say that zero is the initial value or default value of the variable.)
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27. Increment variable value
To add 1 to the numeric variable var
var = var + 1
Or as a shortcut
var +=1
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28. Fundamentals of Programming in VB.Net
Built-in Functions
Functions associates with one or more values and returns a value(output)
Math.sqrt(n):
Returns the square root of n. Math.Sqrt(9) is 3
Int(n):
Returns greatest integer less than or equal to n
Int(9.7) is 3
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29. Fundamentals of Programming in VB.Net
Built-in Functions
Math.Round(n, r):
number n rounded to r decimal places
Math.Round(2.317,1) is 2.3
Math.Round(2.7) is 3
When n is halfway between two successive
whole number, then it rounds to the nearest
even number
Math.Round(2.5) is 2
Math.Round(3.5) is 4
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30. Fundamentals of Programming in VB.Net
Integer Data Type
An integer is a whole number
Declaring an integer variable:
Dim varName As Integer
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31. Multiple Declarations
multiple-declaration statements :
Dim a, b As Double
Dim a As Double, b As Integer
Dim c As Double = 2, b As Integer = 5
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32. Fundamentals of Programming in VB.Net
Three Types of Errors
Syntax error – grammatical errors
misspellings, omissions,incorrect
punctuation
Run-time error
occurs when program is running
Logic error
program doesn’t perform as it is intended
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33. Fundamentals of Programming in VB.Net
Strings
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34. Fundamentals of Programming in VB.Net
Strings
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35. Fundamentals of Programming in VB.Net
Strings
String literal
a sequence of characters treated as a single item, surrounded by “”
String variable
a name used to refer to a string
Dim varName As String
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36. Fundamentals of Programming in VB.Net
Variables and Strings
Private Sub btnDisplay_Click(...) Handles btnDisplay.Click
Dim today As String
today = "Monday"
With lstOutput.Items
.Clear()
.Add("hello")
.Add(today)
End With
End Sub
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37. Using Text Boxes for Input and Output
The contents of a text box is a string
input
strVar = txtBox.Text
Output (ReadOnly = true)
txtBox.Text = strVar
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38. Fundamentals of Programming in VB.Net
Data Conversion
Type-casting
Converts data from one type to another
such as CDblr, Cint, CStr
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39. Data Conversion numVar = CDbl(txtBox.Text) txtBox.Text = CStr(numVar)
Converts a String to a Double
Converts a number to a string
CType(numVar,string)
Convert.ToString(numVar)
numVar.ToString Str(numVar)
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40. Fundamentals of Programming in VB.Net
Data Conversion
All conversions to String are considered to be widening, regardless of whether strict semantics are used.
Special case
Nothing - empty string literal ""
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41. Fundamentals of Programming in VB.Net
Concatenation
Combining two strings into a new string.Concatenation is represented by “&”
Dim str1 As String = “My GPA is A "
Dim Str2 As String = “in Winter 2002"
txtOutput.Text = str1 & str2
displays
My GPA is A in Winter 2002
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42. Fundamentals of Programming in VB.Net
Concatenation
Combining strings with numbers into a string
Dim str1 As String = “My grade is “
Dim grade As Double = 89
Dim str2 As String = “in Winter 2002"
txtOutput.Text = str1 & grade & str2
displays
My GPA is 89 in Winter 2002
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43. Fundamentals of Programming in VB.Net
ANSI Character Set
A numeric representation for every key on the keyboard. The numbers are ranging from 32 to 255
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44. Fundamentals of Programming in VB.Net
ANSI Character Set
If n is between 32 and 255, str
Chr(n):returns the string consisting of the
character with ANSI value n
Chr(65) A
Asc(str):returns the ANSI value of the first
character of str
Asc(“Apple”)
32 & Chr(176) & “Fahrenheit ° Fahrenheit
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45. String Properties and Methods
A string is an object, like controls, has both properties and methods.
Length
ToUpper
Trim
ToLower
IndexOf
Substring
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46. Fundamentals of Programming in VB.Net
String Properties
str.Length:
the number of characters in str
“Tacoma".Length is 5
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47. Fundamentals of Programming in VB.Net
String methods
str.ToUpper
with all letters of str capitalized
“Tacoma".ToUpper is TACOMA.
str.ToLower
with all letters of str in lowercase format
“TCC1926".ToLower is tcc1926
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48. Fundamentals of Programming in VB.Net
String Methods
str.Trim
with all leading and trailing spaces deleted
“IT” & “ 201 ".Trim is IT201
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49. Fundamentals of Programming in VB.Net
String Methods
str.Substring(m,n)
substring consisting of n characters
beginning with the character in position m in
str
“Washington”.Substring(0,4) is “Wash”
str.Substring(m)
substring beginning with the character in
position m in str until the end of str
“Washington”.Substring(2) is “shington”
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50. Fundamentals of Programming in VB.Net
String Methods
str.IndexOf(substr)
-1 if substr is a substring of str
beginning position of the first occurrence
of substr in str
"fanatic".IndexOf("ati") is 3.
"fanatic".IndexOf("nt") is –1.
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51. Fundamentals of Programming in VB.Net
String Methods
str.IndexOf(substr,n)
the position of the first occurrence of
substr in str in position n or greater
"fanatic".IndexOf(“a”, 3) is 3.
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52. Fundamentals of Programming in VB.Net
The Empty String
zero-length string ""
lstBox.Items.Add("") skips a line
txtBox.Text = "“ or
txtBox.Clear() clear the text box
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53. Initial Value of a String
A string should be assigned a value before being used
By default the initial value is Nothing
Strings can be given a different initial value as follows:
Dim today As String = "Monday“
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54. Fundamentals of Programming in VB.Net
Option Strict
The Option Strict statement must appear before any other code
Restricts implicit data type conversions to only widening conversions
Provides compile-time notification of data lost conversions
Generates an error for any undeclared variable
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55. Fundamentals of Programming in VB.Net
Option Strict
The default is Off
Option Strict { On | Off }
On:
Optional. Enables Option Strict checking
Off :
Optional. Disables Option Strict checking
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56. Fundamentals of Programming in VB.Net
Option Strict
Example
Option Strict On
Dim MyVar As Integer
Dim Obj As Object
MyVar = 1000
MyVar = ‘ Data lost
MyInt = 10 ' Undeclared variable
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57. Internal Documentation
Begin the line with an apostrophe
Benefits:
Easy to understand the program
Easy to read long programs because the purposes of individual pieces can be determined at a glance.
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58. Line-Continuation Character
A long line of code can be continued on another line by using underscore (_) preceded by a space
msg = "640K ought to be enough " & _
"for anybody. (Bill Gates, 1981)"
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59. Fundamentals of Programming in VB.Net
Input and Output
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60. Fundamentals of Programming in VB.Net
Input and Output
Formatting Output with Format Functions
Formatting Output with Zones
Reading Data from Files
Getting Input from an Input Dialog Box
Using a Message Dialog Box for Output
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61. Fundamentals of Programming in VB.Net
Format Functions
FormatNumber(n,r)
FormatCurrency(n,r)
FormatPercent(n,r)
return a string value
n - a number, an numeric expression or a
string to be formatted
r - the number of decimal places
default value is 2
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62. Formatting Output with Format Functions
String Value
FormatNumber( ,1)
FormatNumber(1 + 2)
12,345.6
3.00
FormatCurrency( ,2)
FormatCurrency(-100)
$12,345.63
($100.00)
FormatPercent(0.185,2)
FormatPercent(“0.07”)
18.50%
7.00%
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63. Formatting Output with Zones
Line up items in columns
Use a fixed-width font such as Courier New
Divide the characters into zones with a format string.
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64. Formatting output with zones
Zone width
Dim fmtStr As String = "{0, 15}{1, 10}{2, 8}“
lstOutput.Items.Add(String.Format(fmtStr, _
data0, data1, data2))
Zone number
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65. Formatting output with zones
A colon and formatting symbol after width to specially format numeric data
Zone Format
Number to be formatted
Number displayed
{1,12:N3}
{1,12:N0}
34.6 34
{1,12:C1}
$1234.6
{1,-12:P}
0.569
56.90%
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66. Formatting Output with Zones
Zone width
left adjusted if preceded with minus sign, right adjusted otherwise
Spaces between the successive pairs of brackets will be displayed in the corresponding zones in the output.
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67. Formatting Output with Zones
Dim fmtStr As String = “{0,10} {1,12}”
With 1stOutput.Items
.Add(“123”)
End With
Displays
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68. Fundamentals of Programming in VB.Net
Inputting Data
Read data stored in files and accessed with a StreamReader object
Supplied by the user with an input dialog box.
InputBox(prompt, title)
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69. Fundamentals of Programming in VB.Net
Input data from a file
Establish a communication link between computer and the disk drive for reading data from disk
Dim readerVar As IO.StreamReader = _
IO.File.OpenText(filespec)
Read data in order, one at a time, from the file with the ReadLine method assuming the file contains one item of data per line.
strVar = readerVar.ReadLine
terminate the communications link
readerVar.Close()
1. Execute a statement of the form
Dim readerVar As IO.StreamReader
A StreamReader is an object from the Input/Output class that can read a stream of
characters coming from a disk or coming over the Internet. The Dim statement
declares the variable readerVar to be of type StreamReader.
2. Execute a statement of the form
readerVar = IO.File.OpenText(filespec)
where filespec identifies the file to be read. This statement establishes a communi-cations
link between the computer and the disk drive for reading data from the disk.
Data then can be input from the specified file and assigned to variables in the pro-gram.
This assignment statement is said to “open the file for input.”
Just as with other variables, the declaration and assignment statements in Steps
2 and 3 can be combined into the single statement
Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec)
3. Read items of data in order, one at a time, from the file with the ReadLine method.
Each datum is retrieved as a string. A statement of the form
strVar = readerVar.ReadLine
causes the program to look in the file for the next unread line of data and assign it
to the variable strVar. The data can be assigned to a numeric variable if it is first
converted to a numeric type with a statement such as
numVar = CDbl(readerVar.ReadLine)
Note: If all the data in a file have been read by ReadLine statements and another item
is requested by a ReadLine statement, the item retrieved will have the value Nothing.
4. After the desired items have been read from the file, terminate the communications
link set in Step 3 with the statement
readerVar.Close()
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70. Getting Input from an Input Dialog Box
stringVar = InputBox(prompt, title)
fileName = InputBox("Enter the name " _
& "of the file containing the " & _
"information.", "Name of File")
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71. Using a Message Dialog Box for Output
MsgBox(prompt, , title)
MsgBox("Nice try, but no cigar.", , "Consolation")
MsgBox(prompt, , title)
is executed, where prompt and title are strings, a message dialog box appears with prompt
displayed and the title bar caption title and stays on the screen until the user presses
Enter, clicks on the box in the upper-right corner, or clicks OK. For instance, the state-ment
MsgBox("Nice try, but no cigar.", , "Consolation")
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