1. Data Types 1

3. Single or Double ?
Visual Basic provides data type Single for storing single-precision floating-point numbers.
Data type Double requires more memory to store a floating-point value, but is more accurate than type Single.
Type Single is useful in applications that need to conserve memory and do not require the accuracy provided by type Double.

4. Dim statement declares variable Dim varname As type [ = initexpr ]
Declaring a Variable
Dim statement declares variable
Dim varname As type [ = initexpr ]
varname is variable name
As type contains data type of variable
Optional initexpr contains the initial value of a variable

5. Initialize a variable when declaring it
Declaring a Variable
Initialize a variable when declaring it
New to VB .NET
Declare an Integer variable and store the value 30 in the variable
Dim mintYearTerm As Integer = 30

6. Declaring a Variable
Possible to declare multiple variables on the same line
Dim mintYearTerm, mintMonthTerm As Integer

7. Declaring a Variable Dim I as Integer , S As String I = 10 S = “11”
console.WriteLine( I + S )  21
console.WriteLine( I & S )  1011

8. Declaring a Variable Dim dExpiration As Date dExpiration = #1/1/2003#
Dim dnewExpiration As Date
dnewExpiration = dExpiration . AddYears(3)

9. Declaring Constants Declare constants with the Const statement.
Constants are similar to variables – constants are values that are stored to memory locations; however, a constant cannot have its value change during program execution – constant values are generally fixed over time.
Examples:
Const SALES_TAX_RATE_SINGLE As Single = F
Const BIG_STATE_NAME_STRING As String = "Alaska"
Const TITLE_STRING As String = "Data Entry Error"
Const MAX_SIZE_INTEGER As Integer = 4000

10. Declaring Constants
Follow these rules for assigning numeric values to constants:
You can use numbers, a decimal point, and a plus (+) or minus (-) sign.
Do not include special characters such as a comma, dollar sign, or other special characters.
Append one of these characters to the end of the numeric constant or variable to denote a data type declaration. If you do not use these, a whole number is assumed to be Integer and a fractional value is assumed to be Double.
Decimal D 40.45D
Double R R
Integer I 47852I
Long L L
Short S 2588S
Single F F

11. Strings
Such as sentences, words, letters of the alphabet, names, telephone numbers& addresses.
A string constant is a sequence of characters that is treated as a single item.

12. Strings quote1 = “ The ball game isn’t over “
quote2 = “ until it is over “
quote = quote1 & “ , “ & quote2
console.writeLine ( quote ) 
The ball game isn’t over , until it is over

13. String Manipulation Chr (65)  A Asc (“Apple”)  65 Asc(“Ahmad”)  65
“32” & chr(176) & “Fahrenheit” 
32°Fahrenheit

14. String Manipulation - Example
Dim firstName, secondName, fullName As String
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
firstName = TextBox1.Text
secondName = TextBox2.Text
fullName = firstName & " " & secondName
TextBox3.Text = fullName
End Sub 

15. Method Equals String1.Equals(“….“) True or False variable
String.Equals(Str1,Str2)True or False
namespace

16. CompareTo Str1.compareTo (str2) 0 if equal
-1 if str1 < str2 …. ASCII codes
if str1 > str2

17. String Functions Left (str , n ) Left(“Welcome”,3) Wel
Right(str,n )Right(“Welcome”,4) come
Mid (“Welcome”,5,2)  om
Ucase (“Welcome”)  WELCOME
Trim (“ “) 

18. String Functions Len (“Welcome”) = 7 Len (“Just a moment”) = 13

19. String Functions InStr (“Welcome”,”come”)  4
InStr (“Just a moment”,” “)  5
InStr (“Welcome”,” end”)  0

20. Some String Functions Len = .Length Mid = .SubString
Replace = Replace
InStr = IndexOf
UCase = ToUpper
LCase = ToLower
Split = Split
Join = .Join

21. Substring function Dim s As String = "Welcome to the world"
s = s.Substring(8) ‘ “to the world”
Dim r As String = "Welcome to the world"
r = r.SubString(8, 6) ‘ “to the”

22. IndexOf function Dim r As Integer
TextBox1.Text = "Welcome to the grand parade"
TextBox2.text = "grand“
r = TextBox1.Text.IndexOf(TextBox2.Text)
‘ if r > 0 the word is find and r is the position of the where it starts; else the word is not found.

23. Replace Function
This code would produce a message replacing the word 'fool' with 'brave bloke’:
Dim i As String = "Only a fool goes outside in the cold without a coat on"
i = i.Replace("fool", "brave bloke")
To define the point where the Replace function starts searching the string, include the number of characters you wish to start from in the command.
Not only does this example only replace the second 'e' with an 'E', it cuts off the string from the point you specify. The outcome of the line below would be 'TEst' MsgBox(Replace("Test Test", "e", "E", 6))

24. StrReverse Function
If you wish to flip around the front and back end of a string, then the StrReverse(string) is for you.
It is used in the following way. This would pop up a message saying ‘looc si 112pac’
MsgBox(StrReverse(“cap211 is cool"))

25. Boolean Data Type It stores True (1) / False (0)
Any non-zero value will be considered as TRUE.
These variables are combined with the logical operators.. AND, OR & NOT.

26. Examining Variable Types
IsNumeric()
IsDate()
System.Date.IsLeapYear (2001)  False

27. Byte Data Type Holds integer in the range 0  255
Or signed Byte  128
Dim A,B As Byte
A =233
B=50
Console.writeLine ( A + B )
you can do CInt(A) + CInt(B)

28. Converting Input Data Types
Text property always stores string values, even if the string looks like a number.
Parse method – converts a string value to an equivalent numeric value for storage to a numeric variable.
Parse means to examine a string character by character and convert the value to another format such as decimal, integer, or string.
Dim QuantityInteger As Integer = Integer.Parse(TextBox2.Text)

29. Converting Output Data Types
In order to display numeric variable values as output the values must be converted from numeric data types to string in order to store the data to the Text property of a TextBox control. Use the ToString method.
TextBox2.Text = QuantityInteger.ToString()

30. Conversion Between Data Types
1. Methods belong to the System.Convert class
ToInt16 converts value to a Short
ToInt32 converts value to an Integer
ToInt64 converts value to a Long
ToDouble converts value to a Double
ToSingle converts value to a Single
ToString converts value to a String

31. Conversion Between Data Types
Dim msngInput As Single = 3.44
Dim mstrInput As String = "3.95"
Dim mintOutput As Integer
Dim msngOutput As Single
Convert a Single to an Integer
mintOutput = System.Convert.ToInt32(msngInput)
Convert a String to an Integer
mintOutput = System.Convert.ToInt32(mstrInput)
Convert a String to a Single
msngOutput = System.Convert.ToSingle(mstrInput)

32. Conversion Between Data Types
2. CType and named functions:
CType method
Dim A As string = “34.56”
Dim B As Double
B = CType ( A , Double) / 1.14
Older versions of VB used named functions to convert values. Examples are the CDec (convert to Decimal) and CInt (convert to Integer):
PriceDecimal = CDec(TextBox1.Text)
QuantityInteger = CInt(TextBox2.Text)
CDate, CDec, CStr, CLng, CChar, CBool, CByte

33. Implicit Conversion
Implicit Conversion – this is conversion by VB from a narrower to wider data type (less memory to more memory) – this is done automatically as there is no danger of losing any precision.
In this example, an integer (4 bytes) is converted to a double (8 bytes):
BiggerNumberDouble = SmallerNumberInteger

34. Conversion – Summary Rules
Use the Parse method to convert a string to a number or to parse the value in a textbox control.
Use the Convert method to convert a type of number to a different type of number

35. Chapter 4- Control Structures: Part 1

36. Outline
4.1   Introduction 4.2   Algorithms 4.3   Pseudocode 4.4   Control Structures 4.5   If/Then Selection Structure 4.6   If/Then/Else Selection Structure 4.7   While Repetition Structure 4.8   Do While/Loop Repetition Structure 4.9   Do Until/Loop Repetition Structure 4.10   Assignment Operators 4.11   Formulating Algorithms: Case Study 1 (Counter- Controlled Repetition) 4.12   Formulating Algorithms with Top-Down, Stepwise Refinement: Case Study 2 (Sentinel-Controlled Repetition)

37. 4. 13. Formulating Algorithms with Top-Down, Stepwise. Refinement:
4.13   Formulating Algorithms with Top-Down, Stepwise Refinement: Case Study 3 (Nested Control Structures) 4.14   Formulating Algorithms with Top-Down, Stepwise Refinement: Case Study 4 (Nested Repetition Structures) 4.15   Introduction to Windows Application Programming

38. Control Structures
Normally, statements in a program are executed one after another in the order in which they are written. This is called sequential execution.
A transfer of control occurs when an executed statement does not directly follow the previously executed statement in the written program.

39. Control Structures
Bohm and Jacopini’s work demonstrated that all programs could be written in terms of only three control structures:
the sequence structure,
the selection structure,
the repetition structure.

40. Control Structures Selection Structures If/Then If/Then/Else
Single-selection structure
If/Then/Else
Double-selection structure
Select Case
Multiple-selection structure

41. Control Structures Repetition Structures While Do While/Loop
Do/Loop While
Do Until/Loop
Do/Loop Until
For/Next
For Each/Next

42. Control Structures Visual Basic has 11 control structures: Sequence,
Three types of selection,
Seven types of repetition.
Each program is formed by combining as many of each type of control structure as is necessary.

43. If/Then Selection Structure
It is a single-entry/single-exit structure
Example
If studentGrade >= 60 Then
Console.WriteLine(“Passed”)
End If

44. If/Then Selection Structure
The preceding If/Then selection structure also could be written on a single line as
If studentGrade >= 60 Then Console.WriteLine("Passed")
In the multiple-line format, all statements in the body of the If/Then are executed if the condition is true.
In the single-line format, only the statement after the Then keyword is executed if the condition is true.
Writing the closing End If keywords after a single-line If/Then structure is a syntax error.

45. If/Then Selection Structure
Grade >= 60
true
Console.WriteLine(“Passed”)
false
Fig. 4.3 Flowcharting a single-selection If/Then structure.

46. If/Then/Else Selection Structure
The If/Then/Else selection structure allows the programmer to specify that a different action (or sequence of actions) be performed when the condition is true than when the condition is false.

47. If/Then/Else Selection Structure
Grade >= 60
true
Console.WriteLine(“Passed”)
false
Console.WriteLine(“Failed”)
Fig. 4.4 Flowcharting a double-selection If/Then/Else structure.

48. If/Then/Else Selection Structure
Example
If studentGrade >= 60 Then
Console.WriteLine(“Passed”)
Else
Console.WriteLine(“Failed”)
End If

49. If/Then/Else Selection Structure
The VB Editor tries to help you write If statements.
When in the code view window, if you type the keyword If and press Enter, the VB editor automatically adds the keywords Then and End If. You can add the Else branch as necessary.
The VB editor will try to correct errors. If you type EndIf with no space, the editor will correct this and add the required space.
If you type Else with a coding statement on the line, the editor will add a colon between Else and the coding statement – the colon is a statement separator.

50. If/Then/Else Selection Structure
Illegal Syntax
If HoursDecimal <= 40D Then
RegularPayCheckBox.Checked = True
Else RegularPayCheckBox.Checked = False
End If
VB Editor Correction with Colon
Else : RegularPayCheckBox.Checked = False
Preferred Syntax
Else
RegularPayCheckBox.Checked = False
If you type Else with a coding statement on the line, the editor will add a colon between Else and the coding statement

51. Nested If/Then/Else
Nested If/Then/Else structures test for multiple conditions by placing If/Then/Else structures inside other If/Then/Else structures.
Most Visual Basic programmers prefer to write the nested If/Then/Else structure
using the ElseIf keyword.

52. Nested If/Then/Else
For example, the following code will print “A” for exam grades greater than or equal to 90, “B” for grades in the range 80–89, “C” for grades in the range 70–79, “D” for grades in the range 60–69 and “F” for all other grades.

53. While Repetition Structure
Allows the programmer to specify that an action should be repeated, depending on the value of a condition
Example (pseudocode)
While there are more items on my shopping list
Purchase next item
Cross it off my list

54. Write a program that finds the first power of two larger than 1000?
Failure to provide the body of the structure with an action that causes the condition to become false creates an infinite loop

55. While Repetition Structure
product <= 1000
true
product = product * 2
false
Fig. 4.6 Flowchart of the While repetition structure.

56. Do While/Loop Repetition Structure
This structure behaves like the While repetition structure

57. DoWhile.vb Program Output
Write a program to find the first power of two larger than 1000?
DoWhile.vb Program Output
Failure to provide the body of the structure with an action that causes the condition to become false creates an infinite loop

58. Do While/Loop Repetition Structure
product <= 1000
true
product = product * 2
false
Fig. 4.8 Flowchart of a Do While/Loop repetition structure.

59. Do Until/Loop Repetition Structure
Unlike the While and Do While/Loop repetition structures, the Do Until/Loop repetition structure tests a condition for falsity for repetition to continue.
Statements in the body of a Do Until/Loop are executed repeatedly as long as the loop-continuation test evaluates to false.

60. DoUntil.vb Program Output
once again consider a program designed to find the first power of two larger than 1000.
DoUntil.vb Program Output
The loop ends when the condition becomes true

61. Do Until/Loop Repetition Structure
false
product > 1000
product = product * 2
true
Fig Flowcharting the Do Until/Loop repetition structure.

62. Assignment Operators
Fig Assignment operators.

63. Assignment.vb Program Output
Calculates a power of two using the exponentiation assignment operator.
Assignment.vb Program Output

64. Assignment Operators
Although the symbols =, +=, -=, *=, /=, \=, ^= and &= are operators, we do not include them in operator-precedence tables.
When an assignment statement is evaluated,
the expression to the right of the operator is always evaluated first, then assigned to the
variable on the left.
Unlike Visual Basic’s other operators, the assignment operators can only occur once in a statement.

65. Property ReadOnly = true
Space Counter Example
Property ReadOnly = true

66. Space Counter Example Public Class Form1
Private Sub btnCount_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCount.Click
Dim i, counter As Integer, A As String
counter = 0
For i = 1 To Len(txtString.Text)
A = Mid(txtString.Text, i, 1)
If A = " " Then
counter = counter + 1
Else
txtStringNoSpace.Text = txtStringNoSpace.Text & A
End If
Next i
txtSpacesNo.Text = counter
End Sub
Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
txtString.Clear()
txtSpacesNo.Text = ""
txtStringNoSpace.Text = ""
End Class

67. A MUST…
You must practice lots of string manipulation examples check the following websites:

68. Case Study 1 (Counter-Controlled Repetition)
Uses counter: Variable that specifies the number of times that a set of statements will execute
Example:
A class of ten students took a quiz. The grades (integers in the range from 0 to 100) for this quiz are available to you. Determine the class average on the quiz.

70. Program Output Enter integer grade: 89 Enter integer grade: 70
Class average is 74.5

71. Case Study 2 (Sentinel-Controlled Repetition)
Develop a class-averaging program that averages an arbitrary number of grades each time the program is run.
In the first class-average example, the number of grades (10) was known in advance.
In this example, no indication is given of how many grades are to be input. The program must process an arbitrary number of grades.
How can the program determine when to stop the input of grades? How will it know when to calculate and print the class average?

72. Case Study 2 (Sentinel-Controlled Repetition)
One way to solve this problem is to use a special value called a sentinel value (also called a signal value, a dummy value or a flag value) to indicate “end of data entry.”
The user inputs all grades and then types the sentinel value to indicate that the last grade has been entered.
It is crucial to employ a sentinel value that cannot be confused with an acceptable input value.
Grades on a quiz are normally nonnegative integers, thus –1 is an acceptable sentinel value for this problem.

73. In sentinel-controlled repetition, a value is read before the program reaches the While structure
Test division by zero
print the value of average in the command window as a fixed-point number.

74. Program Output Enter Integer Grade, -1 to Quit: 97
Class average is 85.67

75. Case Study 3 (Nested-Control Structure)
A college offers a course that prepares students for the state licensing exam for real estate brokers. Last year, 10 of the students who completed this course took the licensing examination. The college wants to know how well its students did on the exam. You have been asked to write a program to summarize the results. You have been given a list of the 10 students. Next to each name is written a “P” if the student passed the exam and an “F” if the student failed the exam.
Your program should analyze the results of the exam as follows:
1. Input each exam result (i.e., a “P” or an “F”). Display the message “Enter result” each time the program requests another exam result.
2. Count the number of passes and failures.
3. Display a summary of the exam results, indicating the number of students who passed and the number of students who failed the exam.
4. If more than 8 students passed the exam, print the message “Raise tuition.”

76. The If/Then/Else structure is a nested control
The If/Then/Else structure is a nested control. It is enclosed inside the While.
Identifier vbCrLf is the combination of the carriage return and linefeed characters

77. Program Output

78. Case Study 4 (Nested-Repetition Structure)
Write a program that draws in the command window a filled square consisting solely of * characters.
The side of the square (i.e., the number of * characters to be printed side by side) should be input by the user and should not exceed 20.

79. Three levels of nesting

80. Program Output

81. Introduction to Windows Application Programming
In console applications, execution starts from Main.
In Windows applications, if you want a method like main you must create a method that executes when the form is loaded into memory during program execution.
Like Main, this method is invoked when the program is run.
Double-clicking the form in design view adds a method named FrmASimpleProgram_Load to the class, which is responsible for that

82. Introduction to Windows Application Programming
Fig Method FrmASimpleProgram_Load containing program code.

83. Conclusion
Normally, statements in a program are executed one after another in the order in which they are written. This is called sequential execution.
• Various Visual Basic statements enable the programmer to specify that the next statement to be executed might not be the next one in sequence. This is called a transfer of control.
Bohm and Jacopini’s work demonstrated that all programs could be written in terms of only three control structures—the sequence structure, the selection structure and the repetition structure.

84. Conclusion
Failure to provide in the body of a While or Do While/Loop structure an action that eventually causes the condition to become false is a logic error. Normally, such a repetition structure never terminates, resulting in an error called an “infinite loop.”
Failure to provide the body of a Do Until/Loop structure with an action that eventually causes the condition in the Do Until/Loop to become true creates an infinite loop.
Data types Double and Single store floating-point numbers. Data type Double requires more memory to store a floating-point value, but is more accurate and generally more efficient than type Single

85. Conclusion
In Counter-controlled the number of repetitions is known before the loop begins executing.
In sentinel-controlled repetition, the number of repetitions is not known before the loop begins its execution.