VB.NET - Sub Examples - Dot Net Perls

Subs, functions. In VB.NET, Subs and Functions contain behavior. A Sub procedure returns no value. Functions return a value, often based on a variable.

Parameters. Procedures optionally have argument lists and formal parameters. A parameter influence a procedure's behavior. Parameters can be passed ByVal or ByRef.

ByVal, ByRef

Main args

Example sub. We declare and call a Sub procedure. We use different syntaxes to call the procedure. The program also shows XML comments. Subroutines return no value to the caller.

Start The Main Sub first calls the WriteArguments subroutine with a single line of arguments.

Note The WriteArguments sub prints 5 integers on separate lines. Console.WriteLine, too, is a Sub.

Note 2 We can separate a long line when calling or declaring a function. We use an underscore as a line continuation.

Result This program uses Console.WriteLine and prints ten numbers to the console screen.

Module Module1 Sub Main() ' ' Call the Sub Procedure, which returns no value. ' ... You can put all the arguments on one line. ' WriteArguments(1, 2, 3, 4, 5) ' ' Call the Sub Procedure again. ' ... You can use the line continuation marker to break up the lines. ' WriteArguments(1000, _ 2000, _ 3000, _ 4000, _ 5000) End Sub ''' <summary> ''' Prints out the five arguments. ''' </summary> ''' <param name="param1">Description 1.</param> ''' <param name="param2">Description 2.</param> ''' <param name="param3">Description 3.</param> ''' <param name="param4">Description 4.</param> ''' <param name="param5">Description 5.</param> ''' <remarks>Made by Dot Net Perls.</remarks> Sub WriteArguments(ByVal param1 As Integer, _ ByVal param2 As Integer, _ ByVal param3 As Integer, _ ByVal param4 As Integer, _ ByVal param5 As Integer) Console.WriteLine(param1) Console.WriteLine(param2) Console.WriteLine(param3) Console.WriteLine(param4) Console.WriteLine(param5) End Sub End Module

1 2 3 4 5 1000 2000 3000 4000 5000

XML comments. To add an XML-based comment to a function, type three single-quote characters. Then insert the text inside the XML tags that appear.

Info XML comments are used in Visual Studio's interface. They make large programs easier to develop.

Module Module1 ''' <summary> ''' Type 3 apostrophes on top of a Function. ''' </summary> ''' <returns></returns> Function Example() As Integer Return 100 End Function Sub Main() End Sub End Module

Dim, As. We use the Dim and As keywords within a method body. Dim begins a variable declaration. And with As we specify that variable's type.

Here We declare a variable with the identifier (name) of "value." We assign it initially to 100.

Info The "As" keyword specifies the type of the variable. Sometimes it is not required—the compiler can determine the types itself.

Module Module1 Sub Main() ' The Dim keyword is used to declare a variable. ' ... With As we specify its type. Dim value As Integer = 100 Console.WriteLine(value) End Sub End Module

100

Functions. Let us contrast the Function keyword to the Sub keyword. The Sub does not return a value to its caller. But a Function returns a value.

Function

Module Module1 Function MultiplyByTwo(ByVal test As Integer) As Integer Return test * 2 End Function Sub Main() ' Call the Function with an argument of 5. Console.WriteLine(MultiplyByTwo(5)) End Sub End Module

Shared. A Function or Sub can be shared throughout all instances of the enclosing class. An instance reference is not needed to call a Shared Function.

Shared

Class Utility ''' <summary> ''' Displays a helpful message. ''' </summary> Public Shared Sub Message() Console.WriteLine("Hello world") End Sub End Class Module Module1 Sub Main() ' We do not use a Utility instance to call the shared Sub. Utility.Message() End Sub End Module

Hello world

Comment. A comment is best written at the level of intention. We explain what the code is meant to accomplish. If a computation is important, a comment makes it more prominent.

Info Rem stands for an explanatory remark. All characters following REM are not code statements.

Next When 3 apostrophes are at the start of the comment, this is an XML comment. These are parsed by Visual Studio.

Finally The simplest comment form starts with a single apostrophe. This is probably the easiest syntax for comments.

Module Module1 REM This is Module1. ''' <summary> ''' This is an XML comment. ''' </summary> ''' <remarks>Called at program start.</remarks> Sub Main() REM Get square root of 225. Dim value As Double = Math.Sqrt(225) ' Print value. (Other comment syntax.) ' ... Sometimes it helps to indent comments. Console.WriteLine(value) End Sub End Module

Underscore. This language does not allow line breaks everywhere. A newline signals the end of a statement. But an underscore allows a statement to span many lines.

Start The first program uses a statement on a single line. This statement uses generic types.

Next The second program uses the underscore syntax at the end of lines. This means the statement can continue on the next line.

Module Module1 Sub Main() Dim longerVariableName As Dictionary(Of String, KeyValuePair(Of Boolean, .... longerVariableName("a") = Nothing End Sub End Module

Module Module1 Sub Main() Dim longerVariableName _ As Dictionary(Of String, KeyValuePair(Of Boolean, Integer)) = _ New Dictionary(Of String, KeyValuePair(Of Boolean, Integer))(5000) longerVariableName("a") = Nothing End Sub End Module

AddressOf. This operator allows us to reference a Function or Sub by its name. We can then pass the result to another Function. Here, Array.FindIndex requires a Predicate argument.

AddressOf

Note The AddressOf IsMatch syntax returns a suitable function as a Predicate instance.

Note 2 With AddressOf we can change a Function or Sub name into an argument, a variable, that we can pass to other procedures.

Module Module1 Function IsMatch(ByVal item As String) As Boolean Return item.Length = 4 End Function Sub Main() Dim items() As String = {"cat", "apple", "baby"} ' Use AddressOf to specify IsMatch as the Predicate. Dim index As Integer = Array.FindIndex(items, AddressOf IsMatch) Console.WriteLine(index) End Sub End Module

Summary. The Sub procedure syntax is often used in VB.NET programs. Subroutines (Subs) return no value. We compared Subs with Functions.