1. Programming with Visual Basic .NET
Using Classes and Method
Week # 9
Tariq Ibn Aziz
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2. The System Namespace
The System namespace contains fundamental classes and base classes
System.String
System.Integer
System.Array
System.Console
System.Convert
System.Math
System.Random
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3. Math Class
Math class provides constants and static methods for trigonometric, logarithmic, and other common mathematical functions
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4. Shared Methods in Math Class
Polymorphism example
Public Const E As Double
Public Const PI As Double
Overloads Public Shared Function Abs (Double) as Double
Overloads Public Shared Function Abs (Decimal) as Decimal
Overloads Public Shared Function Abs (Short) as Short
Overloads Public Shared Function Abs (Integer) as Integer
Overloads Public Shared Function Abs (Long) as Long
Overloads Public Shared Function Abs (Single) as Single
Public Shared Function Cos (ByVal d As Double) As Double
Public Shared Function Sin (ByVal d As Double) As Double
Public Shared Function Tan (ByVal d As Double) As Double
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5. Shared Methods in Math Class
Public Shared Function Max (Double, Double) As Double
Public Shared Function Max (Byte, Byte) As Byte
Public Shared Function Min (Double, Double) As Double
Public Shared Function Min (Byte, Byte) As Byte
Public Shared Function Pow (ByVal x As Double, ByVal y As Double) As Double
Public Shared Function Sqrt (ByVal x As Double) As Double
Overloads Public Shared Function Round (Double) As Double
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6. Shared Methods Example 1
Imports System.Console
Imports System
Public Module MathClass
Sub Main()
WriteLine(Math.Max(-8,-4))
WriteLine(Math.Min(-8,-4))
WriteLine(Math.Abs(-84))
End Sub
End Module
Output: -4 -8 84
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7. Shared Methods Example 2
Imports System.Console
Imports System
Public Module EandPI
Sub Main()
WriteLine("E=" & Math.E)
WriteLine("PI=" & Math.PI)
End Sub
End Module
Output:
E =
PI=
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8. Shared Methods Exercise
Write a program that displays the square root of 23.45
Write a program that displays the value of 2 raised to the power 12
Write a program to compute the hypotenuse of a right triangle whose sides are 4.5 and 8.9 units long
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9. String Class
The String class provides several good examples of instance methods
An instance variable is associated with an object.
It is necessary to create an instance of class in order to read or write it.
The syntax of accessing instance variable is as follows:
objRef.varName
The syntax of accessing shared or static variable is as follows:
String.varName
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10. String Class
The class String is defined in System class, which automatically imported into every program you write.
Dim strFirst As String = "Goodbye"
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11. Array of String Imports System.Console Public Module StringArray
Sub Main()
Dim deptName(3) As String
deptName(0)="Accounting"
deptName(1)="Human Resources"
deptName(2)="Sales"
WriteLine("0=" & deptName(0))
WriteLine("1=" & deptName(1))
WriteLine("2=" & deptName(2))
End Sub
End Module
OUTPUT:
0 = Accounting
1 = Human Resource
2 = Sales
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12. Instance Methods of String Class
Determines whether two String objects have the same value
Function Equals (Object) As Boolean
Compares this instance with a specified object
Function CompareTo (Object) As Integer
Determines whether the end of this instance matches the specified String
Function EndsWith( String ) As Boolean
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13. Instance Methods of String Class
Determines whether two String objects have the same value.
Function Equals( Object ) As Boolean
Reports the index of the first occurrence of a String, or one or more characters, within this instance.
Function IndexOf( Char ) As Integer
Retrieves a substring from this instance
Function Substring( Integer ) As String
Function Substring( Integer, Integer ) As String
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14. Instance Methods of String Class
Returns a copy of this String in lowercase.
Function ToLower() As String
Converts the value of this instance to a String
Function ToString() As String
Returns a copy of this String in uppercase.
Function ToUpper() As String
Removes all occurrences of a set of specified characters from the beginning and end of this instance
Function Trim() As String
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15. Shared Methods of String Class
Compares two specified String objects
Shared Function Compare (String, String) As Integer
Concatenates one or more instances of String
Shared Function Concat (Object, Object) As String
Creates a new instance of String with the same value as a specified String
Shared Function Copy( String ) As String
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16. Instance Method of String Class Example-I
Imports System.Console
Public Module First10Char
Sub Main()
Dim s0 As String = "One Two Three Four "
WriteLine(S0.substring(0,10)) ' One Two Th
End Sub
End Module
Output
Instance Method
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17. Instance Method of String Class Example-II
Imports System.Console
Public Module First10Char
Sub Main()
Dim s1 As String = "One"
Dim s2 As String = "Two"
Dim s3 As String = "One"
WriteLine(S1.compareTo(s2)) '-1
WriteLine(S2.compareTo(s1)) ' 1
WriteLine(S1.compareTo(s3)) ' 0
End Sub
End Module
Output
Instance Method
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18. Instance Method of String Class Example-III
Imports System.Console
Public Module DollarAmount
Sub Main()
Dim s1 As String = "The Total Amount is $45.78"
Dim i As Integer= 0
i= s1.indexOf("$")
Dim s2 AS String = s1.substring(i)
WriteLine(s2)
End Sub
End Module
$45.78
Output
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19. Shared Method of String Class Example-IV
Imports System.Console
Public Module DollarAmount
Sub Main()
Dim s1 As String = "CA-"
Dim s2 As String = "121"
Dim s3 As String
s3= String.concat(s1,s2)
WriteLine(s3)
End Sub
End Module
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20. Shared Method of String Class Example-V (Contd.)
Imports System
Class Sample
Public Shared Sub Main()
Dim str1 As String = "abc"
Dim str2 As String = "xyz"
Console.WriteLine("1) str1 = '{0}'", str1)
Console.WriteLine("2) str2 = '{0}'", str2)
Console.WriteLine("Copy...")
str2 = [String].Copy(str1)
Console.WriteLine("3) str1 = '{0}'", str1)
Console.WriteLine("4) str2 = '{0}'", str2)
End Sub 'Main
End Class 'Sample
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21. Example-V Output ' 'This example produces the following results:
'1) str1 = 'abc'
'2) str2 = 'xyz'
'Copy...
'3) str1 = 'abc'
'4) str2 = 'abc'
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22. String Class Exercise
Write a program that displays the substring formed by the last ten characters of a string.
Hint: Use Length Property of String Class
A string contains five numbers separated by commas. Write a program that displays the last number
Hint: Search for String Members in help and look for LastIndexOf ( ) method
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23. Integer Class Instance Methods of Integer Class
A System.Int32 object encapsulates a simple Integer value.
A System.Int32 class defines MaxValue and MinValue as two of its static/Shared variable
Instance Methods of Integer Class
Function CompartTo (Object) As Integer
Function Equals (Object) As Boolean
Function ToString () As String
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24. Integer Class Shared Methods of Integer Class
Overloads public Shared Function Parse (String) As Integer
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25. Integer Class Instance Method Example
Imports System
Class Sample
Public Shared Sub Main()
Dim str1 As Object = "Hello"
Dim v1 As Integer = Str1.CompareTo("Hello")
Dim v2 As Integer = Str1.CompareTo("Tariq")
Dim v3 As Integer = Str1.CompareTo("CA121")
Console.WriteLine("V1 = " & V1 )' V1 = 0
Console.WriteLine("V2 = " & V2 )' V2 =-1
Console.WriteLine("V3 = " & V3 )' V3 = 1
End Sub 'Main
End Class
Output
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26. Integer Class Example WriteLine(System.Int32.MinValue) '-2147483648
Imports System.Console
Public Module DollarAmount
Sub Main()
Dim i As System.Int32
WriteLine(i.MaxValue) '
WriteLine(System.Int32.MinValue) '
End Sub
End Module
Output
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27. Integer Class Shared Method Example
Imports System
Class Sample
Public Shared Sub Main()
Dim str1 As String = "125"
Dim no As Integer = Integer.Parse(str1)
Console.WriteLine("Total = " & no + 5 )
End Sub 'Main
End Class
Output
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28. Integer Example Output Imports System.Console
Public Module StringToInt
Sub Main()
Dim s As String = "100"
Dim i as Integer = s
System.console.WriteLine(i) ' 100
i = i + 10
System.console.WriteLine(i) ' 110
End Sub
End Module
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29. Char Class Instance Methods
Public Overridable Function CompareTo (Object) As Integer
Public Overridable Function Equal (Object) As Boolean
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30. Char Class Shared Methods "
Public Shared Shared Function IsControl (Char) As Boolean
Public Shared Function IsDigit (Char) As Boolean
Public Shared Function IsLetter (Char) As Boolean
Public Shared Function IsLower (Char) As Boolean
Public Shared Function IsNumber (Char) As Boolean
Public Shared Function IsPunctuation (Char) As Boolean
Public Shared Function IsSeperator (String,Integer) As Boolean
Public Shared Function IsSymbol (Char) As Boolean
Public Shared Function IsWhiteSpace (String,Integer) As Boolean
"
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31. Char Example imports System.Console Module CharStructure
Public Sub Main()
Dim chA As Char
chA = "A"c
Dim ch1 As Char
ch1 = "1"c
Dim str As String
str = "test string“
' Output: "-1" (meaning 'A' < 'B')
WriteLine(chA.CompareTo("B"c))
WriteLine(chA.Equals("A"c)) ' Output: "True"
WriteLine(Char.GetNumericValue(ch1)) ' Output: "1"
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32. Char Example WriteLine(Char.IsControl(Chr(9))) ' Output: "True"
WriteLine(Char.IsDigit(ch1)) ' Output: "True"
WriteLine(Char.IsLetter(","c)) ' Output: "False"
WriteLine(Char.IsLower("u"c)) ' Output: "True"
WriteLine(Char.IsNumber(ch1)) ' Output: "True"
WriteLine(Char.IsPunctuation("."c)) ' Output: "True"
WriteLine(Char.IsSeparator(str, 4)) ' Output: "True"
WriteLine(Char.IsSymbol("+"c)) ' Output: "True"
WriteLine(Char.IsWhiteSpace(str, 4)) ' Output: "True"
WriteLine(Char.Parse("S")) ' Output: "S"
WriteLine(Char.ToLower("M"c)) ' Output: "m"
WriteLine("x"c.ToString()) ' Output: "x"
End Sub
End Module
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33. Command Line Arguments
' CommandLineArg.vb
Public Module CommandLineArgument
Sub Main()
Dim commands As String
commands = Microsoft.VisualBasic.Command()
System.console.WriteLine (commands)
End Sub
End Module
OUTPUT:
H:\CA121> CommandLineArg Tariq Aziz
Tariq Aziz
H:\CA121> CommandLineArg Hello 123
Hello 123
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34. Command Line Arguments
' CommandLineArg.vb
Public Module CommandLineArgument
Sub Main()
Dim separators As String = " "
Dim commands As String
Dim args() As String
commands = Microsoft.VisualBasic.Command()
args=commands.Split(separators.ToCharArray)
System.console.WriteLine(" Args: " & args.length)
System.console.WriteLine(args(0)) ' Tariq
System.console.WriteLine(args(1)) ' 123
End Sub
End Module
Output
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35. Command Line Arguments
Output:
H:\CA121> CommandLineArg Hello 123
Hello
123
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36. Command Line Arguments
Public Module Add2Arg
Sub Main()
Dim separators As String = " "
Dim commands As String
Dim args() As String
commands = Microsoft.VisualBasic.Command()
args = commands.Split(separators.ToCharArray)
Dim i As Integer = args(0) ' 10
Dim j As Integer = args(1) ' 25
Dim k As integer = i + j
System.console.WriteLine (k) ' 35
End Sub
End Module
Output
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37. Local variables and scope
Local variable are declared inside a method and exist only during its execution
Local variables are only available in their scope only
Imports System.Console
Public Module Add2Arg
Sub Calculate()
Dim a As Integer= 10
Dim b As Integer= 11
WriteLine (a + b) ' 21
End Sub
Sub Main()
Calculate()
WriteLine (a)
End Module
Not Available here
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38. Local variables and scope
Local variables are created upon entry into block and destroyed upon exit
Variable can be defined inside statement block e.g inside do, for, or while loop
Imports System.Console
Public Module Add2Arg
Sub Calculate()
For a As Integer= 1 To 2
Dim b As Integer= 11
WriteLine (b)
Next a
WriteLine (b)'Not visible
End Sub
Sub Main()
Calculate()
End Module
Not Available here
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39. Local variables and scope
Declaring a local variable with the same name as static or instance variable will hide the static and instance variable
Imports System.Console
Dim b As Integer= 15
Public Module Add2Arg
Sub Calculate()
For a As Integer= 1 To 2
Dim b As Integer= 11
WriteLine (b) '11
Next a
WriteLine (b) '15
End Sub
Sub Main()
Calculate()
End Module
It will hide
b=15
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40. Variable Scope Keywords
Keywords specify the variable scope
Private - available only to code within the local class
Public - used outside the class
Friend - used only within the current application or project
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41. Variable Scope
Block scope — available only within the code block in which it is declared
Procedure scope — available only within the procedure in which it is declared
Module scope — available to all code within the module, class, or structure in which it is declared
Namespace scope — available to all code in the namespace
Imports System.Console
Public Module Add2Arg
Dim b As Integer= 15
Sub Calculate()
Dim c As Integer= 13
For a As Integer= 1 To 2
Dim b As Integer= 11
WriteLine (b) '11
Next a
WriteLine (b) '15
WriteLine (c) '13
End Sub
Sub Main()
Calculate()
End Module
Block Scope
Procedure Scope
Module Scope
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42. Block Scope
A block is a set of statements terminated by an End, Else, Loop, or Next statement, for example within a For...Next or If...Then...Else...End If construction. An element declared within a block can be used only within that block. In the following example, the scope of the integer variable Cube is the block between If and End If, and Cube can no longer be referenced when execution passes out of the block:
If N < 1291 Then
Dim Cube As Integer
Cube = N ^ 3
End If
Imports System.Console
Public Module Add2Arg
Sub Calculate()
For a As Integer= 1 To 2
Dim b As Integer= 11
WriteLine (b) '11
Next a
WriteLine (b) 'Not visible
End Sub
Sub Main()
Calculate()
End Module
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43. Procedure Scope
An element declared within a procedure is not available outside that procedure. Only the procedure that contains the declaration can use it. Elements at this level are also known as local elements. You declare them with the Dim statement, with or without the Static keyword.
Imports System.Console
Public Module Add2Arg
Sub Calculate()
Dim b As Integer= 13
For a As Integer= 1 To 2
WriteLine (b) '13
Next a
End Sub
Sub Main()
Calculate()
WriteLine (b) 'Not visible
End Module
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44. Module Scope
For convenience, the single term module level applies equally to modules, classes, and structures. You can declare elements at this level by placing the declaration statement outside of any procedure or block within the module, class, or structure.
Imports System.Console
Public Module Add2Arg
Dim b As Integer= 15
Sub Calculate()
For a As Integer= 1 To 2
WriteLine (b) '15
Next a
End Sub
Sub Main()
Calculate()
End Module
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45. B is visible in namespace because of Public
Namespace Scope
If you declare an element at module level using the Friend or Public keyword, it becomes available to all procedures throughout the namespace in which the element is declared.
Imports System.Console
Public Module Add2Arg
Public B As Integer= 15
Sub Calculate()
For a As Integer= 1 To 2
WriteLine (B) '15
Next a
End Sub
Sub Main()
Calculate()
End Module
B is visible in namespace because of Public
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46. Lifetime Variables
Module, shared, instance, and static variables consume memory resources until your application stops running, so use them only when necessary.
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47. Scope of K is inside the For Loop
Block Scope Exercise
Scope of K is inside the For Loop
Imports System.Console
class VariableScope
Shared Sub Main()
For j As Integer = 0 To 5
Dim k As Integer=100
WriteLine ("j = " & j & ";K = " & k)
k = k + 1
Next j
End Sub
End Class
Output
j = 0; k = 100
j = 1; k = 100
j = 2; k = 100
j = 3; k = 100
j = 4; k = 100
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48. Procedure Scope Exercise
Local variables S and J hide the class variable
class MyObject
Dim S As Short = 400
Dim J As Integer = 200
Sub myMethod()
Dim S As Short = ' local variable
Dim J As Integer = 100 ' local variable
Dim D As Double = 1E100 ' local variable
System.Console.WriteLine (S & "," & J & "," & D)
End Sub
End Class
Class MainClass
public Shared Sub Main()
Dim m As New MyObject
mo.myMethod()
Output:
300,100,1.0E100
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49. Module variables s and j
Module Scope Exercise
Module variables s and j
class MyObject
Dim s As Short = 400
Dim j As Integer = 200
Sub f()
Dim d As Double = 1E100 'local variable
System.Console.WriteLine (s & "," & j & "," & d)
End Sub
public Shared Sub Main()
Dim mo As New MyObject
mo.f()
End Class
Output:
400,200,1.0E100
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50. Argument Passing
All method arguments are passed by value. This means that copies of the arguments are provided to a method. Any changes to those copies are not visible outside the methods
Imports System.Console
Public Module Add2Arg
Sub Print( x As Integer)
x=10
WriteLine ( x ) '10
End Sub
Sub Main()
Dim x As Integer=5
Print( x )
WriteLine ( x ) '5
End Module
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51. Argument Passing
The situation changes when an arrays or object is passed as an argument. In this case entire array or object is not copied, instead only a copy of reference is provided. Therefore any changes to the array or object are visible outside the method. However reference itself is passed by value
Imports System.Console
Class Argument
Shared sub a (k As Integer())
k(0)=11
End Sub
Shared Sub display(k As Integer())
For m As Integer =0 To 3
WriteLine (k(m))
Next m
Shared Sub Main()
Dim k As Integer()={1,2,3,4}
display(k)
a(k)
End Class
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52. Argument Passing (Home Practice)
Imports System.Console
Public Module Add2Arg
Sub GetMaximum(x As Integer, y As Integer )
If x > y Then
WriteLine ( x & " is bigger number" )
Else
WriteLine ( y & " is bigger number" )
End If
End Sub
Sub Main()
GetMaximum( 2 , 3)
End Module
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53. Argument Passing (Home Practice)
Class CallByValue
Shared sub a (j As Integer, k As Integer())
j=7
k(0)=11
End Sub
Shared Sub display (j As Integer, k As Integer())
System.Console.WriteLine ("J=" & j)
For m As Integer =0 To 3
System.Console.WriteLine (k(m))
Next m
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54. Argument Passing (Home Practice)
Shared Sub Main()
Dim j As Integer=5
Dim k As Integer()={1,2,3,4}
display(j, k)
a(j, k)
End Sub
End Class
Output 5
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55. Exercise
Write an application that accepts one command-line argument and displays its Spanish equivalent. For example, the tokens “uno,” “dos,” “tres,” “quatro,” and “cinco” are the Spanish tokens for the numbers “one” through “five”. Create a class with a static method to accomplish this task
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