VB.NET Sub Procedure Examples

Use the Sub keyword for a subroutine. See the syntax for parameters and comments.
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

ByVal: The parameter's location is local. When chanced in a procedure body, no other values are affected.

ByRef: The parameter's location is shared with the calling location. A change is reflected outside the procedure.

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.

WriteArguments: 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.

Underscore: 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.

VB.NET program that uses Sub procedure 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 Output 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.

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.

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

As: This lets us specify the type of the variable. Sometimes this keyword is not required—the compiler can determine the types itself.

VB.NET program that uses Dim, As for local 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 Output 100
Functions. Let us contrast the Function type to the Subtype. The Sub does not return a value to its caller. But a Function returns a value.Function
VB.NET program that uses 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 Output 10
As-keyword. In VB.NET, the As-keyword is used to indicate a type. In a parameter, As describes the type of the parameter. And in a Function, As describes the return value's type.
Multiple return values. Only one value can be placed in a Return statement. To return many values, we can use ByRef arguments or return a Tuple or KeyValuePair.Multiple Return Values
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
VB.NET program that calls Shared Sub 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 Output Hello world
A comment is best written at the level of intention. We explain what the code is meant to accomplish. Comments that simply translate the code to English are less effective.

But: Comments sometimes help emphasize certain aspects of programs. If a computation is important, a comment makes it more prominent.

VB.NET program that uses 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 Output 15
Comment syntax. We use three comment syntax forms. REM stands for an explanatory remark. All characters following REM are not code statements.

And: When three apostrophes are at the start of the comment, this is an XML comment.

XML comments: These are used by Visual Studio to help programmers navigate and discover your code. Certain XML tags can be added.

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

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.

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

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

VB.NET program that uses long statement Module Module1 Sub Main() Dim longerVariableName As Dictionary(Of String, KeyValuePair(Of Boolean, .... longerVariableName("a") = Nothing End Sub End Module VB.NET program that uses with statement on multiple lines 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.

VB.NET program that uses AddressOf 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 Output 2
ParamArray. For a varargs function in VB.NET, we use the ParamArray keyword. Zero or more arguments can be passed where ParamArray is specified.ParamArray
Event, AddHandler, RaiseEvent. An Event contains a group of delegate methods. When the event is raised (with RaiseEvent), all its methods are executed.Event
Extension. An extension method is not an instance method. But it is called with the same syntax as one. We apply the <Extension()> syntax.Extension Method
Lambda expressions. We can use the Sub and Function keywords to declare lambda expressions directly in other method bodies. Lambdas act like any other method.Lambdas
Optional, named arguments. With the Optional keyword, we indicate an argument to a method may be omitted. A default value must be provided. Named arguments are also used.Optional
Recursion. When a Function calls itself, recursion occurs. The ByRef keyword can be useful when implementing recursive algorithms.Recursion
With. The VB.NET language has some syntactic sugar. One example is the With statement. This reduces the typing necessary in some contexts.With
Const. A Const value is used with syntax similar to a field or local variable. But it cannot be reassigned. It can only be initialized.Const
Structures. When a method is called, a structure argument is copied fully to the method's local memory. A Class argument is not—only its reference is copied.Structure
Procedures are everywhere. The Sub procedure syntax is often used in VB.NET programs. Subroutines (Subs) return no value. We compared Subs with Functions.
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