1 Chapter 3 – Fundamentals of Programming in Visual Basic 3.1 Visual Basic Controls 3.2 Visual Basic Events 3.3 Numbers 3.4 Strings 3.5 Input and Output

2 3.1 Visual Basic Controls Invoking Visual Basic Text Box Control Button Control Label Control List Box Control Name Property Fonts / Auto Hide Positioning and Aligning Controls

IN-CLASS EXAMPLE Make a small program or two The following slides show screen shots of the compiler, I’ll keep them up for review. Section 3.3 Numbers Next 3

4 Visual Basic Start Page

5 Start a New Project

6 New Project Dialog Box

7 Initial Visual Basic Screen

8 Toolbox

9 3 Ways to Place a Control from the Toolbox onto the Form Window Double-click Drag Click, Point, and Drag

10 Four Controls at Design Time Text box To select a control, click on it. Sizing handles will appear when a control is selected.

11 Text Box Control Used for input and output When used for output, ReadOnly property is set to True Sizing handles Tasks button

12 Properties Window Categorized view Alphabetical view Press F4 to display the Properties window for the selected control.

13 Properties Window Properties Settings Selected control

14 Some Often Used Properties Text Autosize Font.Name Font.Size ForeColor BackColor ReadOnly

15 Setting Properties Click on property name in left column. Enter its setting into right column by typing or selecting from options displayed via a button or ellipses.

16 Setting the ForeColor Property 1.Click on ForeColor. 2.Click on button at right of settings box. 3.Click on Custom tab to obtain display shown. 4.Click on a color.

17 Font Property 1.Click on Font in left column. 2.Click on ellipsis at right of settings box to obtain display shown, 3.Make selections.

18 Button Control The caption on the button should indicate the effect of clicking on the button. Text property determines caption.

19 Add an "access key"

20 Label Control Used to identify the contents of a text box. Text property specifies caption. By default, label automatically resizes to accommodate caption on one line. When the AutoSize property is set to False, label can be resized manually. Used primarily to obtain a multi-rowed label.

21 List Box Control Initially used to display several pieces of output. Later used to select from a list.

22 The Name Property How the programmer refers to a control in code Setting for Name property near top of Properties window. Name must begin with a letter, be less than 215 characters long, and may include numbers and letters. Use appropriate 3- or 4-character naming prefix

23 Control Name Prefixes ControlPrefixExample buttonbtnbtnCompute labellbllblAddress text boxtxttxtAddress list boxlstlstOutput

24 Renaming the Form Initial name is Form1 The Solution Explorer window lists a file named Form1.vb. To rename the form, change the name of this file to newName.vb newName should begin with prefix frm.

25 Fonts Proportional width fonts take up less space for "I" than for "W" – like Microsoft Sans Serif Fixed-width fonts take up the same amount of space for each character – like Courier New Fixed-width fonts are good for tables.

26 Auto Hide Hides Toolbox when not in use Vertical push pin icon indicates auto hide is disabled. Click the push pin to make it horizontal and enable auto hide. Push pin

27 Positioning Controls Proximity line

28 Aligning Controls Snap line

29 Aligning Controls Snap line

Visual Basic Events An Event Procedure Walkthrough Properties and Event Procedures of the Form The Header of an Event Procedure

31 Event An event is an action, such as the user clicking on a button Usually, nothing happens in a Visual Basic program until the user does something and generates an event. What happens is determined by statements.

32 Sample Statements txtBox.ForeColor = Color.Red txtBox.Visible = True txtBox.Text = “Hello World” General Form: controlName.property = setting

33 Sample Form txtFirst txtSecond btnRed

34 Focus When you click on a text box, a cursor appears in the text box, and you can type into the text box. Such a text box is said to have the focus. If you click on another text box, the first text box loses the focus and the second text box receives the focus.

35 Examples of Events btnShow.Click txtBox.TextChanged txtBox.Leave General Form: controlName.event

36 The three steps in creating a Visual Basic program: 1.Create the interface; that is, generate, position, and size the objects. 2.Set properties; that is, configure the appearance of the objects. 3.Write the code that executes when events occur.

37 Code Window Method Name box Class Name box Page tab

38 Structure of an Event Procedure Private Sub objectName_event(...) Handles objectName.event statements End Sub (...) is filled automatically with (ByVal sender As System.Object, ByVal e As System.EventArgs) Header

39 Code Window Method Name box Class Name box Page tab

40 Create an Outline for an Event Procedure; i.e. header and End Sub 1. Double-click on a control or 2. Use the Class Name and Method Name boxes. (We primarily use the first method.)

41 Sample Form txtFirst txtSecond btnRed Double Click on txtFirst

42 Code for Walkthrough Public Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub End Class

43 IntelliSense Automatically pops up to give the programmer help.

44 Code Window Click tab to return to Form Designer

45 Sample Form txtFirst txtSecond btnRed Double-click on btnRed

46 Code for Walkthrough Public Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub Private Sub btnRed_Click(...) Handles btnRed.Click End Sub End Class

47 Code for Walkthrough Public Class frmDemo Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.Red End Sub End Class

48 Event Procedure txtFirst.Leave Select txtFirst from Class Name box drop-down list. Select Leave from Method Name box drop-down list.

49 Code for Walkthrough Private Sub txtFirst_Leave(...) Handles txtFirst.Leave End Sub Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.Red End Sub

50 Code for Walkthrough Private Sub txtFirst_Leave(...) Handles txtFirst.Leave txtFirst.ForeColor = Color.Black End Sub Private Sub txtFirst_TextChanged(...) Handles txtFirst.TextChanged txtFirst.ForeColor = Color.Blue End Sub Private Sub btnRed_Click(...) Handles btnRed.Click txtFirst.ForeColor = Color.Red End Sub

51 Header of Event Procedure Private Sub btnRed_Click(…) Handles btnRed.Click Identifies event Name, can be changed. Private Sub Button_Press(…) Handles btnRed.Click

52 Handling Multiple Events Private Sub Button_Click(...) Handles btnRed.Click, txtSecond.Leave txtFirst.ForeColor = Color.Red End Sub Event procedure can be invoked by two events.

53 Altering Properties of the Form The following won't work: frmDemo.Text = "Demonstration" The form is referred to by the keyword Me. Me.Text = "Demonstration"

Numbers How to handle numbers in VB Arithmetic Operations Variables Incrementing the Value of a Variable Built-In Functions: Math.Sqrt Int Math.Round

55 Numbers continued The Integer Data Type Multiple Declarations Parentheses Three Types of Errors

56 Arithmetic Operations Numbers are called numeric literals Five arithmetic operations in Visual Basic + addition - subtraction * multiplication / division ^ exponentiation

57 Numeric Expressions * (4 + 5) 2 ^ 3

58 Displaying Numbers Let n be a number or a numeric expression. The statement lstBox.Items.Add(n) displays the value of n in the list box.

Numbers Example List Box Example

60 Example 1: Form

61 Example 1: Code and Output Private Sub btnCompute_Click (...) Handles btnCompute.Click lstResults.Items.Add(5) lstResults.Items.Add(2 * 3) lstResults.Items.Add((2 ^ 3) – 1) End Sub Output 5 in list 6 box 7

62 Example 1: Code using With Private Sub btnCompute_Click (...) Handles btnCompute.Click With lstResults.Items.Add(5).Add(2 * 3).Add((2 ^ 3) – 1) End With End Sub

63 Numeric Variable A numeric variable is a name to which a number can be assigned. Examples: speed distance interestRate balance

64 Variables Declaration: Dim speed As Double Variable name Data type Assignment: speed = 50

65 Initialization Numeric variables are automatically initialized to 0: Dim varName As Double To specify a nonzero initial value Dim varName As Double = 50

66 Numeric Expressions Numeric variables can be used in numeric expressions. Dim balance As Double = 1000 lstBox.Items.Add(1.05 * balance) Output: 1050

67 Assignment Statement Dim numVar1 As Double = 5 Dim numVar2 As Double = 4 numVar1 = 3 * numVar2 lstBox.Items.Add(numVar1) Output: 12

68 Incrementing To add 1 to the numeric variable var var = var + 1 Or as a shortcut var += 1 Or as a generalization var += numeric expression

69 Built-in Functions Functions return a value Math.Sqrt(9) returns 3 Int(9.7) returns 9 Math.Round(2.7) is 3

70 Integer Data Type Variables of type Double can be assigned both whole numbers and numbers with decimals. The statement Dim varName As Integer declares a numeric variable that can only be assigned whole number values between about -2 billion and 2 billion.

71 Multiple Declarations Dim a, b As Double Two other types of multiple-declaration statements are Dim a As Double, b As Integer Dim c As Double = 2, b As Integer = 5

72 Parentheses Parentheses should be used liberally in numeric expressions. In the absence of parentheses, the operations are carried out in the following order: ^, * and /, + and -. Follows standard order of operations

73 Three Types of Errors Syntax error Run-time error Logic error

74 Some Types of Syntax Errors Misspellings lstBox.Itms.Add(3) Omissions lstBox.Items.Add(2 + ) Incorrect punctuation Dim m; n As Integer

75 A Type of Run-time Error Overflow error Dim numVar As Integer = numVar = numVar * numVar

76 A Logical Error Dim average As Double Dim m As Double = 5 Dim n As Double = 10 average = m + n / 2 Value of average will be 10. Should be 7.5.

Strings Variables and Strings Using Text Boxes for Input and Output Concatenation String Properties and Methods: LengthToUpper TrimToLower IndexOfSubstring

78 Strings continued The Empty String Initial Value of a String Option Strict Internal Documentation Line-Continuation Character

79 String Literal A string literal is a sequence of characters surrounded by quotation marks. Examples: "hello" " " "#ab cde?"

80 String Variable A string variable is a name to which a string value can be assigned. Examples: country ssn word firstName

81 String Variable Declaration: Dim firstName As String Variable name Data type Assignment: firstName = "Fred"

82 String Variable You can declare a string variable and assign it a value at the same time. Dim firstName As String = "Fred"

83 Add Method Let str be a string literal or variable. Then, lstBox.Items.Add(str) displays the value of str in the list box.

84 String Variable You can assign the value of one string variable to another. Dim strVar1 As String = "Hello" Dim strVar2 As String = "Goodbye" strVar2 = strVar1 lstOutput.Items.Add(strVar2) Output: Hello

85 Variables and Strings Private Sub btnDisplay_Click(...) Handles btnDisplay.Click Dim today As String today = "Monday" lstOutput.Items.Add("hello") lstOutput.Items.Add(today) End Sub Output: hello Monday

86 Using Text Boxes for Input and Output The contents of a text box is always a string Input example strVar = txtBox.Text Output example txtBox.Text = strVar

87 Data Conversion Because the contents of a text box is always a string, sometimes you must convert the input or output. dblVar = CDbl(txtBox.Text) txtBox.Text = CStr(numVar) Converts a String to a Double Converts a number to a string

88 Concatenation Combining two strings to make a new string quote1 = "We'll always " quote2 = "have Paris." quote = quote1 & quote2 txtOutput.Text = quote & " - Humphrey Bogart" Displays We'll always have Paris. - Humphrey Bogart

89 Appending To append str to the string variable var var = var & str Or as a shortcut var &= str

90 Appending Example Dim var As String = "Good" var &= "bye" txtBox.Text = var OUTPUT: Goodbye

91 String Properties and Methods "Visual".Length is 6. "Visual".ToUpper is VISUAL. "123 Hike".Length is 8. "123 Hike".ToLower is 123 hike. "a" & " bcd ".Trim & "efg" is abcdefg. Note the spaces before and after bcd

92 Positions in a String Positions of characters in a string are numbered 0, 1, 2, …. Consider the string “Visual Basic”. Position 0: V Position 1: i Position 7: B Substring “al” begins at position 4

93 Substring Method Let str be a string. str.Substring(m, n) is the substring of length n, beginning at position m in str. “Visual Basic”.Substring(2, 3) is “sua” “Visual Basic”.Substring(0, 1) is “V”

94 IndexOf Method Let str1 and str2 be strings. str1.IndexOf(str2) is the position of the first occurrence of str2 in str1. (Note: Has value -1 if str2 is not a substring of str1.) "Visual Basic".IndexOf("is") is 1. "Visual Basic".IndexOf("si") is 9. "Visual Basic".IndexOf("ab") is -1.

95 The Empty String The string "", which contains no characters, is called the empty string or the zero-length string. The statement lstBox.Items.Add("") skips a line in the list box. The contents of a text box can be cleared with either the statement txtBox.Clear() or the statement txtBox.Text = ""

96 Initial Value of a String By default the initial value is Nothing Strings can be given a different initial value as follows: Dim today As String = "Monday"

97 Option Strict Visual Basic allows numeric variables to be assigned strings and vice versa, a poor programming practice. To turn this feature off, put the following statement at the very top of the code window Option Strict On

98 Option Strict On for All Programs Select Options from the Tools menu In left pane, expand Projects and Solution Select VB Defaults Set Option Strict to On

99 With Option Strict On Dim dblVar As Double, intVar As Integer Dim strVar As String Not Valid:Replace with: intVar = dblVarintVar = CInt(dblVar) dblVar = strVar dblVar = CDbl(strVar) strVar = intVarstrVar = CStr(intVar)

100 Comments Private Sub btnCompute_Click (...) Handles btnCompute.Click 'Calculate the balance in an account Dim rate As Double 'Annual rate of interest Dim curBalance As Double 'Current balance

101 Internal Documentation 1.Other people can easily understand the program. 2.You can understand the program when you read it later. 3.Long programs are easier to read because the purposes of individual pieces can be determined at a glance.

102 Automatic Colorization Comments – green String literals – maroon Keywords – blue Note: Keywords are words such as Sub, Handles, Private, With, and End that have special meaning in Visual Basic. They cannot be used as variable names.

103 Line-Continuation Character A long line of code can be continued on another line by using an underscore (_) preceded by a space msg = "I'm going to make " & _ "him an offer he can't refuse.“ This is for if your line of code is to long for one line.

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 Using a Masked Text Box for Input

105 Formatting Output with Format Functions FunctionString Value FormatNumber( , 1)12,345.6 FormatCurrency( , 2)$12, FormatPercent(0.183, 0)18%

106 Formatting Output with Zones Use a fixed-width font such as Courier New Divide the characters into zones with a format string. Dim fmtStr As String = "{0, 15}{1, 10}{2, 8}" lstOutput.Items.Add(String.Format(fmtStr, _ data0, data1, data2))

107 Formatting Output with Zones Dim fmtStr As String = "{0, -15}{1, 10}{2, 8}" lstOutput.Items.Add(String.Format(fmtStr, _ data0, data1, data2)) Here, 15 was preceded by a minus sign. This produces left justification in 0 th zone. There will be right justification in the other two zones.

108 Zone Formatting Symbols Symbols: N, C, and PEffect on zone :NrFormatNumber(data, r) :CrFormatCurrency(data, r) :PrFormatPercent(data, r) Dim fmtStr As String = "{0,15:N1}{1,10:C2}{2,8:P0}"

109 Reading Data from Files Data can be stored in files and accessed with a StreamReader object. We assume that the files are text files (that is, have extension.TXT) and have one piece of data per line.

110 Sample File: PAYROLL.TXT Mike Jones John Smith Name Hourly wage Number of hours worked

111 Steps to Use StreamReader Execute a statement of the form Dim readerVar As IO.StreamReader = _ IO.File.OpenText(filespec) or the pair of statements Dim readerVar As IO.StreamReader readerVar = IO.File.OpenText(filespec)

112 Steps to Use StreamReader Read items of data in order, one at a time, from the file with the ReadLine method. strVar = readerVar.ReadLine After the desired items have been read from the file, terminate the communications link readerVar.Close()

113 Example using StreamReader Dim name As String Dim wage, hours As Double Dim sr As IO.StreamReader = _ IO.File.OpenText("PAYROLL.TXT") name = sr.ReadLine wage = CDbl(sr.ReadLine) hours = CDbl(sr.ReadLine) lstBox.Items.Add(name & ": " & wage * hours) OUTPUT: Mike Jones:

114 Comment on Example Consider lstBox.Items.Add(name & ": " & wage * hours) The ampersand automatically converted wage * hours into a string before concatenating. We didn’t have to convert wage * hours with CStr.

115 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") Title Prompt

116 Using a Message Dialog Box for Output MsgBox(prompt, 0, title) MsgBox("Nice try, but no cigar.", 0, _ "Consolation") Title Prompt

117 Masked Text Box Similar to an ordinary text box, but has a Mask property that restricts what can be typed into the masked text box.

118 Input Mask Dialog Box

119 Mask A Mask setting is a sequence of characters, with 0, L, and & having special meanings. 0 Placeholder for a digit. L Placeholder for a letter. & Placeholder for a character or space.

120 Sample Masks State abbreviation: LL Phone number: Social Security Number: License plate: &&&&&&