Unit 03

Uses Try…Catch…Finally blocks to handle errors in a controlled and readable way. It is object-oriented and more reliable.

Try
    ' risky code
Catch ex As Exception
    ' handling code
Finally
    ' cleanup code
End Try

Module Module1
    Sub Main()
        Try
            Dim a As Integer = 10
            Dim b As Integer = 0
            Dim c As Integer

            c = a \ b   ' causes error
        Catch ex As Exception
            MsgBox("Error occurred")
        Finally
            MsgBox("Program finished")
        End Try
    End Sub
End Module

Features:

• Handles specific exceptions
• Supports multiple Catch blocks
• Finally always runs
• High readability and safety
• Recommended in VB.NET

Uses On Error statements. It is the older method, less flexible, and not recommended for modern applications.

Types of On Error:

• On Error GoTo label
• On Error Resume Next
• On Error GoTo 0

Module Module1
    Sub Main()
        On Error GoTo ErrHandler

        Dim a As Integer = 10
        Dim b As Integer = 0
        Dim c As Integer

        c = a \ b

        Exit Sub

ErrHandler:
        MsgBox("Error occurred")
    End Sub
End Module

Features:

• Old VB style
• Uses labels and jumps
• Harder to maintain
• Less structured
• Not recommended for new applications

A procedure is a block of statements that performs a task but does not return any value.

Sub ProcedureName([parameters])
    ' statements
End Sub

Module Module1
    Sub ShowMessage()
        MsgBox("Welcome to VB.NET")
    End Sub

    Sub Main()
        ShowMessage()
    End Sub
End Module

Features:

• Does not return a value
• Called using its name directly
• Uses Sub…End Sub
• Can take parameters
• Used for performing actions

A function is a block of code that performs a task and returns a value to the calling program.

Function FunctionName([parameters]) _
        As DataType
    ' statements
    Return value
End Function

Module Module1
    Function Add(ByVal a As Integer, _
                 ByVal b As Integer) As Integer
        Return a + b
    End Function

    Sub Main()
        Dim result As Integer
        result = Add(10, 20)
        MsgBox(result)
    End Sub
End Module

Features:

• Returns a value
• Uses Function…End Function
• Must specify return type
• Uses Return statement
• Can accept parameters

A dynamic array is an array whose size can be changed at runtime using the ReDim statement. Size is not fixed at compile time.

Dim arrayName() As DataType
ReDim arrayName(size)

Module Module1
    Sub Main()
        Dim arr() As Integer

        ReDim arr(4)   ' size = 5 elements

        arr(0) = 10
        arr(1) = 20
        arr(2) = 30

        MsgBox(arr(1))
    End Sub
End Module

ReDim Preserve — resizes without losing existing data:

ReDim Preserve arr(9)

Features:

• Size decided at runtime
• Uses ReDim statement
• Flexible memory usage
• Use Preserve to retain data

A jagged array is an array of arrays where each row can have a different number of columns. It is not a rectangular matrix.

Dim jaggedArray()() As DataType

Module Module1
    Sub Main()
        Dim jagged()() As Integer = _
            New Integer(2)() {}

        jagged(0) = New Integer() {1, 2}
        jagged(1) = New Integer() {3, 4, 5}
        jagged(2) = New Integer() {6}

        MsgBox(jagged(1)(2))
    End Sub
End Module

Features:

• Array of arrays
• Rows can have different lengths
• Memory efficient for irregular data
• Access using double index arr(i)(j)