VB.Net- Lecture 4

MARWARI COLLEGE, RANCHI

(AN AUTONOMOUS UNIT OF RANCHI UNIVERSITY FROM 2009)

- Prakash Kumar, Dept. of CA

-Raju Manjhi, Dept of CA

__________________________________________________________________________________

A Select Case statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each select case.

Syntax:

The syntax for a Select Case statement in VB.Net is as follows:

Select [ Case ] expression

    [ Case expressionlist

        [ statements ] ]

    [ Case Else

        [ elsestatements ] ]

End Select

e.g.

Module Module1

    Sub Main()

        Dim x As Integer

        x = 1

        Select Case x

            Case 1

                Console.WriteLine("CA")

            Case 2

              

Console.WriteLine("IT")

            Case Else

                Console.WriteLine("Invalid choice")

        End Select

        Console.WriteLine("Your choice is {0} ", x)

        Console.Read()

    End Sub

End Module

VB.Net - Loops

A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages:

VB.Net provides following types of loops to handle looping requirements.

Loop Type	Description
Do Loop	It repeats the enclosed block of statements while a Boolean condition is True or until the condition becomes True. It could be terminated at any time with the Exit Do statement.
For...Next	It repeats a group of statements a specified number of times and a loop index counts the number of loop iterations as the loop executes.
For Each...Next	It repeats a group of statements for each element in a collection. This loop is used for accessing and manipulating all elements in an array or a VB.Net collection.
While... End While	It executes a series of statements as long as a given condition is True.
With... End With	It is not exactly a looping construct. It executes a series of statements that repeatedly refer to a single object or structure.
Nested loops	You can use one or more loops inside any another While, For or Do loop.

  Note:

For Each...Next

With... End With

Nested loops

Will be discussed later.

B. Loop

     i.  For ………Next

1. Module Module1

    Sub Main()

        Dim i As Integer

        For i = 1 To 5 Step 1

            Console.WriteLine(i)

        Next

       

        Console.Read()

    End Sub

End Module

2.

Module Module1

    Sub Main()

        Dim i As Integer

        For i = 5 To 1 Step -1

            Console.WriteLine(i)

        Next i

       

        Console.Read()

    End Sub

End Module

ii. While ….. End While

 Module Module1

    Sub Main()

        Dim i As Integer

        i = 1

        While i <= 5

            Console.WriteLine(i)

            i = i + 1

        End While

        Console.Read()

    End Sub

End Module

iii. Do ….. Loop

Module Module1

    Sub Main()

        Dim i As Integer

        i = 1

        Do

            Console.WriteLine(i)

            i = i + 1

            If (i > 5) Then

                Console.Read()

                Exit Sub

            End If

        Loop

    End Sub

End Module

Go through the video for execution of the programs and practice more questions:

Practice programs:
1. Nested Loop :Pyramid of asterix
Module Module1

    Sub Main()
        Dim i, j, k As Integer
        For i = 1 To 5
            For k = 5 To i Step -1
                Console.Write(" ")
            Next
            For j = 1 To i
                Console.Write("* ")
            Next
            Console.WriteLine()
        Next
        Console.Read()
    End Sub

End Module

2. Reverse of a number
Module Module1

    Sub Main()
        Dim num, re, reve As Integer
        Console.Write("Enter a number to reverse: ")
        num = Console.ReadLine
        While (num > 0)
            re = num Mod 10
            reve = reve * 10 + re
            num = num \ 10 ' Integer Division
        End While
        Console.WriteLine("Reverse=" & reve)

        Console.Read()
    End Sub


End Module

2. Matrix

Module Module1

    Sub Main()
        Dim a(,) As Integer = {{1, 2}, {3, 4}}

        Dim i, j As Integer
        For i = 0 To 1
            For j = 0 To 1
                Console.Write("   " & a(i, j))
            Next
            Console.WriteLine()
        Next
        Console.Read()
    End Sub


End Module

Note:
array is declared as 
a(n)- single dimension
a(m,n)- double dimension