VB.Net/Language Basics/ByVal

Array parameter passed by Value and by Reference

<source lang="vbnet"> Imports System public class MainClass

  Shared Sub Main()
       Dim A As Integer() = {1, 2, 3, 4, 5}
       Dim B As Integer()
       B = A
       Console.WriteLine("Initial state ArrayTests")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("Array A:")
       DisplayArray(A)
       Console.WriteLine("Array B")
       DisplayArray(B)
       FunctionPassArrayByReference1(B)
       Console.WriteLine("After FunctionPassArrayByReference1")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("Array A:")
       DisplayArray(A)
       Console.WriteLine("Array B")
       DisplayArray(B)
       A(0) = 1
       B = A
       FunctionPassArrayByReference2(B)
       Console.WriteLine("After FunctionPassArrayByReference2")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("Array A:")
       DisplayArray(A)
       Console.WriteLine("Array B")
       DisplayArray(B)
       A(0) = 1
       B = A
       FunctionPassArrayByValue1(B)
       Console.WriteLine("After FunctionPassArrayByValue1")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("Array A:")
       DisplayArray(A)
       Console.WriteLine("Array B")
       DisplayArray(B)
       A(0) = 1
       B = A
       FunctionPassArrayByValue2(B)
       Console.WriteLine("After FunctionPassArrayByValue2")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("Array A:")
       DisplayArray(A)
       Console.WriteLine("Array B")
       DisplayArray(B)

  End Sub
  Shared Public Sub FunctionPassArrayByReference1(ByRef Y As Integer())
       Y(0) = 5
   End Sub
  Shared Public Sub FunctionPassArrayByReference2(ByRef Y As Integer())
       Dim NewArray As Integer() = {2, 3, 4, 5, 6}
       Y = NewArray
   End Sub
  Shared Public Sub FunctionPassArrayByValue1(ByVal Y As Integer())
       Y(0) = 5
   End Sub
  Shared Public Sub FunctionPassArrayByValue2(ByVal Y As Integer())
       Dim NewArray As Integer() = {2, 3, 4, 5, 6}
       Y = NewArray
   End Sub
  Shared Public Sub DisplayArray(ByVal Y As Integer())
       Dim X As Integer
       For X = 0 To UBound(Y)
           Console.Write(Y(X).ToString)
           If X <> UBound(Y) Then
               Console.Write(", ")
           Else
               Console.WriteLine()
           End If
       Next
   End Sub

End Class

      </source>

Array passed By Value

<source lang="vbnet"> Imports System Public Class MainClass

   Shared Sub Main(ByVal args As String())
     Dim i As Integer
     Dim firstArray As Integer()
     Dim firstArrayCopy As Integer()
     firstArray = New Integer() {1, 2, 3}
     firstArrayCopy = firstArray
     Console.WriteLine("Test passing array reference using ByVal.")
     Console.WriteLine("Contents of firstArray before calling FirstDouble: ")
     For i = 0 To firstArray.GetUpperBound(0)
        Console.WriteLine(firstArray(i))
     Next
     " pass firstArray using ByVal
     FirstDouble(firstArray)
     Console.WriteLine("Contents of firstArray after calling FirstDouble: ")
     " print contents of firstArray
     For i = 0 To firstArray.GetUpperBound(0)
        Console.WriteLine(firstArray(i) & " ")
     Next
     " test whether reference was changed by FirstDouble
     If firstArray Is firstArrayCopy Then
        Console.WriteLine("The references are equal.")
     Else
        Console.WriteLine("The references are not equal.")
     End If

   End Sub
  " procedure modifies elements of array and assigns 
  " new reference (note ByVal)
  Shared Sub FirstDouble(ByVal array As Integer())
     Dim i As Integer
     " double each element value
     For i = 0 To array.GetUpperBound(0)
        array(i) *= 2
     Next
     " create new reference, assign it to array
     array = New Integer() {11, 12, 13}
  End Sub

End Class

      </source>

Function with pass by value Parameter

<source lang="vbnet"> Imports System Public Class MainClass

 Shared Sub Main()
   Dim A() As String = {"HELLO", "GOODBYE"}
   Console.WriteLine("Original first item in array is: " _
     & A(0))
   Console.WriteLine("Original second item in array is: " _
     & A(1))
   AFunction(A)
   Console.WriteLine("After passing by value first item in array now is: " _
     & A(0))
   Console.WriteLine("After passing by value second item in array is: " _
     & A(1))
 End Sub
 Shared Sub AFunction(ByVal Foo As String())
   Foo(0) = "GOODBYE"
   Foo(1) = "HELLO"
 End Sub

End Class

      </source>

Modify Array Element By Value

<source lang="vbnet"> Imports System Public Class MainClass

   Shared Sub Main(ByVal args As String())
     Dim array1 As Integer() = New Integer() {1, 2, 3, 4, 5}
     Dim i As Integer
     Console.WriteLine( "The values of the original array are:" & vbCrLf )
     " display original elements of array1
     For i = 0 To array1.GetUpperBound(0)
        Console.WriteLine(  "  " & array1(i) )
     Next
     Console.WriteLine(  vbCrLf & vbCrLf & _
        "EFFECTS OF PASSING ARRAY ELEMENT " & _
        "BY VALUE:" & vbCrLf & vbCrLf & "array1(3) " & _
        "before ModifyElementByVal: " & array1(3) )
     " array element passed by value
     ModifyElementByVal(array1(3))

   End Sub
  Shared Sub ModifyElementByVal(ByVal element As Integer)
     Console.WriteLine(  vbCrLf & "Value received in " & _
        "ModifyElementByVal: " & element )
     element *= 2
     Console.WriteLine(  vbCrLf & "Value calculated in " & _
        "ModifyElementByVal: " & element )
  End Sub " ModifyElementByVal

End Class

      </source>

Object parameter passed by Value and by Reference

<source lang="vbnet"> Imports System public class MainClass

  Shared Sub Main()
       Dim A As New MyObject()
       Dim B As MyObject = A
       A.X = 1
       Console.WriteLine("Initial state")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       FunctionPassObjectByReference1(B)
       Console.WriteLine("After FobjByRef1")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       A.X = 1
       B = A
       FunctionPassObjectByReference2(B)
       Console.WriteLine("After FobjByRef2")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       A.X = 1
       B = A
       FunctionPassObjectByValue1(B)
       Console.WriteLine("After FobjByVal1")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       A.X = 1
       B = A
       FunctionPassObjectByValue2(B)
       Console.WriteLine("After FobjByVal2")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       
  End Sub
  Shared Public Sub FunctionPassObjectByReference1(ByRef Y As MyObject)
       Y.X = 5
   End Sub
  Shared Public Sub FunctionPassObjectByReference2(ByRef Y As MyObject)
       Y = New MyObject()
       Y.X = 5
   End Sub
  Shared Public Sub FunctionPassObjectByValue1(ByVal Y As MyObject)
       Y.X = 5
   End Sub
  Shared Public Sub FunctionPassObjectByValue2(ByVal Y As MyObject)
       Y = New MyObject()
       Y.X = 5
   End Sub
   Class MyObject
       Public X As Integer
   End Class

End Class

      </source>

Passing arrays and individual array elements to procedures

<source lang="vbnet"> Imports System Public Class MainClass

   Shared Sub Main(ByVal args As String())
     Dim array1 As Integer() = New Integer() {1, 2, 3, 4, 5}
     Dim i As Integer
     Console.WriteLine( "The values of the original array are:" & vbCrLf )
     " display original elements of array1
     For i = 0 To array1.GetUpperBound(0)
        Console.WriteLine(  "  " & array1(i) )
     Next
     ModifyArray(array1) " array is passed by reference
     Console.WriteLine(  vbCrLf & _
        "The values of the modified array are:" & vbCrLf )
     " display modified elements of array1
     For i = 0 To array1.GetUpperBound(0)
        Console.WriteLine("  " & array1(i) )
     Next
   End Sub
  " procedure modifies array it receives (note ByVal)
  Shared Sub ModifyArray(ByVal arrayParameter As Integer())
     Dim j As Integer
     For j = 0 To arrayParameter.GetUpperBound(0)
        arrayParameter(j) *= 2
     Next
  End Sub " ModifyArray

End Class

      </source>

Squares three values ByVal and ByRef, displays results

<source lang="vbnet"> Imports System Public Class MainClass

   Shared Sub Main(ByVal args As String())
     Dim number1 As Integer = 2
     Console.WriteLine("Passing a value-type argument by value:")
     Console.WriteLine("Before calling SquareByValue, " & _
        "number1 is {0}", number1)
     SquareByValue(number1)  " passes number1 by value
     Console.WriteLine("After returning from SquareByValue, " & _
        "number1 is {0}" & vbCrLf, number1)
     Dim number2 As Integer = 2
     Console.WriteLine("Passing a value-type argument" & _
        " by reference:")
     Console.WriteLine("Before calling SquareByReference, " & _
        "number2 is {0}", number2)
     SquareByReference(number2) " passes number2 by reference
     Console.WriteLine("After returning from " & _
        "SquareByReference, number2 is {0}" & vbCrLf, number2)
     Dim number3 As Integer = 2
     Console.WriteLine("Passing a value-type argument" & _
        " by reference, but in parentheses:")
     Console.WriteLine("Before calling SquareByReference " & _
        "using parentheses, number3 is {0}", number3)
     SquareByReference((number3)) " passes number3 by value
     Console.WriteLine("After returning from " & _
        "SquareByReference, number3 is {0}", number3)
   End Sub

  " squares number by value (note ByVal keyword)
  Shared Sub SquareByValue(ByVal number As Integer)
     Console.WriteLine("After entering SquareByValue, " & _
        "number is {0}", number)
     number *= number
     Console.WriteLine("Before exiting SquareByValue, " & _
        "number is {0}", number)
  End Sub " SquareByValue
  " squares number by reference (note ByRef keyword)
  Shared Sub SquareByReference(ByRef number As Integer)
     Console.WriteLine("After entering SquareByReference" & _
        ", number is {0}", number)
     number *= number
     Console.WriteLine("Before exiting SquareByReference" & _
        ", number is {0}", number)
  End Sub " SquareByReference

End Class

      </source>

String parameter passed by Value and by Reference

<source lang="vbnet"> Imports System public class MainClass

  Shared Sub Main()
       Dim A As String = "Hello"
       Dim B As String
       B = A
       Console.WriteLine(Chr(10) + "Initial state StringTests")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A: " + A + " B: " + B)
       FunctionPassStringByReference1(B)
       Console.WriteLine("After FunctionPassStringByReference1")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A: " + A + " B: " + B)
       A = "Hello"
       B = A
       FunctionPassStringByReference2(B)
       Console.WriteLine("After FunctionPassStringByReference2")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A: " + A + " B: " + B)
       A = "Hello"
       B = A
       FunctionPassStringByReference3(B)
       Console.WriteLine("After FunctionPassStringByReference3")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("Are A and B equal? " + (A = B).ToString())
       Console.WriteLine("A: " + A + " B: " + B)
       A = "Hello"
       B = A
       FunctionPassStringByValue1(B)
       Console.WriteLine("After FunctionPassStringByValue1")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A: " + A + " B: " + B)
       A = "Hello"
       B = A
       FunctionPassStringByValue2(B)
       Console.WriteLine("After FunctionPassStringByValue2")
       Console.WriteLine("Are A and B the same? " + (A Is B).ToString())
       Console.WriteLine("A: " + A + " B: " + B)
  End Sub
  Shared Public Sub FunctionPassStringByReference1(ByRef Y As String)
       Mid$(Y, 1, 1) = "A"
   End Sub
  Shared  Public Sub FunctionPassStringByReference2(ByRef Y As String)
       Y = "Hello"
   End Sub
  Shared  Public Sub FunctionPassStringByReference3(ByRef Y As String)
       Mid$(Y, 1, 1) = "H"
   End Sub
  Shared  Public Sub FunctionPassStringByValue1(ByVal Y As String)
       Mid$(Y, 1, 1) = "A"
   End Sub
  Shared  Public Sub FunctionPassStringByValue2(ByVal Y As String)
       Y = "Hello"
   End Sub

End Class

      </source>

Structure parameter passed by Value and by Reference

<source lang="vbnet"> Imports System public class MainClass

  Shared Sub Main()
       Dim A As MyStruct
       Dim B As MyStruct
       A.X = 1
       B = A
       Console.WriteLine("Initial state StructTests")
       Console.WriteLine("Are A and B the same? " + (A.Equals(B)).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       FunctionPassStructureByReference1(B)
       Console.WriteLine("After FunctionPassStructureByReference1")
       Console.WriteLine("Are A and B the same? " + (A.Equals(B)).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       A.X = 1
       B = A
       FunctionPassStructureByReference2(B)
       Console.WriteLine("After FunctionPassStructureByReference2")
       Console.WriteLine("Are A and B the same? " + (A.Equals(B)).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       A.X = 1
       B = A
       FunctionPassStructureByValue(B)
       Console.WriteLine("After FunctionPassStructureByValue")
       Console.WriteLine("Are A and B the same? " + (A.Equals(B)).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       A.X = 1
       B = A
       FStructByVal2(B)
       Console.WriteLine("After FStructByVal2")
       Console.WriteLine("Are A and B the same? " + (A.Equals(B)).ToString())
       Console.WriteLine("A.x: " + A.X.ToString() + " B.x " + B.X.ToString())
       
  End Sub
  Shared Public Sub FunctionPassStructureByReference1(ByRef Y As MyStruct)
       Y.X = 5
   End Sub
  Shared Public Sub FunctionPassStructureByReference2(ByRef Y As MyStruct)
       Y = New MyStruct()
       Y.X = 5
   End Sub
  Shared Public Sub FunctionPassStructureByValue(ByVal Y As MyStruct)
       Y.X = 5
   End Sub
  Shared Public Sub FStructByVal2(ByVal Y As MyStruct)
       Y = New MyStruct()
       Y.X = 5
   End Sub

   Structure MyStruct
       Public X As Integer
   End Structure

End Class

      </source>