Visual Basic.NET How to Program (PDF)

Chapter 6 Procedures 201
not necessary to do so except with type String. Although they technically are reference
types, String arguments cannot be modified directly when passed with keyword ByVal,
due to some subtle details of the String data type, which we discuss in Chapter 15,
Strings, Characters and Regular Expressions.
1 ' Fig. 6.12: ByRefTest.vb
2 ' Demonstrates passing by reference.
3
4 Module modByRefTest
5
6 ' squares three values ByVal and ByRef, displays results
7 Sub Main()
8 Dim number1 As Integer = 2
9
10 Console.WriteLine("Passing a value-type argument by value:")
11 Console.WriteLine("Before calling SquareByValue, " & _
12 "number1 is {0}", number1)
13 SquareByValue(number1) ' passes number1 by value
14 Console.WriteLine("After returning from SquareByValue, " & _
15 "number1 is {0}" & vbCrLf, number1)
16
17 Dim number2 As Integer = 2
18
19 Console.WriteLine("Passing a value-type argument" & _
20 " by reference:")
21 Console.WriteLine("Before calling SquareByReference, " & _
22 "number2 is {0}", number2)
23 SquareByReference(number2) ' passes number2 by reference
24 Console.WriteLine("After returning from " & _
25 "SquareByReference, number2 is {0}" & vbCrLf, number2)
26
27 Dim number3 As Integer = 2
28
29 Console.WriteLine("Passing a value-type argument" & _
30 " by reference, but in parentheses:")
31 Console.WriteLine("Before calling SquareByReference " & _
32 "using parentheses, number3 is {0}", number3)
33 SquareByReference((number3)) ' passes number3 by value
34 Console.WriteLine("After returning from " & _
35 "SquareByReference, number3 is {0}", number3)
36
37 End Sub ' Main
38
39 ' squares number by value (note ByVal keyword)
40 Sub SquareByValue(ByVal number As Integer)
41 Console.WriteLine("After entering SquareByValue, " & _
42 "number is {0}", number)
43 number *= number
44 Console.WriteLine("Before exiting SquareByValue, " & _
45 "number is {0}", number)
46 End Sub ' SquareByValue
47
Fig. Fig. 6.12 6.12 ByVal and ByRef used to pass value-type arguments (part 1 of 2).