Microsoft Visual Basic .NET Language Reference  

First Chapter

• #Const Directive
• #ExternalSource Directive
• #If...Then...#Else Directives
• #Region Directive
• & Operator
• &= Operator
• * Operator
• *= Operator
• + Operator
• += Operator
• - Operator
• -= Operator
• / Operator
• /= Operator
• = Operator
• \ Operator
• \= Operator
• ^ Operator
• ^= Operator
• Add Method
• AddHandler Statement
• AddressOf Operator
• Alias
• And Operator
• AndAlso Operator
• Ansi
• AppActivate Function
• AppWinStyle Enumeration
• As
• Asc, AscW Functions
• Assembly
• Auto
• Beep Function
• Boolean Data Type
• ByRef
• Byte Data Type
• ByVal

#Const Directive

Defines conditional compiler constants for Visual Basic.

#Const 
constname 
= 
expression

Parts

constname

Required. String. Name of the constant being defined.

expression

Required. Literal, other conditional compiler constant, or any combination that includes any or all arithmetic or logical operators except Is.

Remarks

Conditional compiler constants are always private to the file in which they appear. You cannot create public compiler constants using the #Const directive; you can create them only in the user interface.

You can use only conditional compiler constants and literals in expression. Using a standard constant defined with #Const causes an error. Conversely, you can use constants defined with the #Const keyword only for conditional compilation. Constants also can be undefined, in which case they have a value of Nothing.

Example

This example uses the #Const directive.

#Const MyCountry = "USA"



#Const Version = "8.0.0012"



#Const CustomerNumber = 36

See Also

#If...Then...#Else Directives, Const Statement

#ExternalSource Directive

Indicates a mapping between source lines and text external to the source, such as an .aspx file.

# ExternalSource( 
StringLiteral , 
IntLiteral 
)


   [ 
LogicalLine+ ]



# End ExternalSource

Parts

StringLiteral

The path to the external source.

IntLiteral

The line number of the first line of the external source.

Logical Line

The line where the error occurs in the external source.

# End ExternalSource

Terminates the #ExternalSource block.

Remarks

A source file may include external source directives that indicate a mapping between source lines and text external to the source, so if errors are encountered during compilation, they are identified as coming from the external source. External source directives have no effect on compilation and may not be nested. They are intended for internal use by the application only.

#If...Then...#Else Directives

Conditionally compiles selected blocks of Visual Basic code.

#If 
expression 
Then


   
statements


[ 
#ElseIf 
expression 
Then


   [ 
statements ]


...

#ElseIf 
expression 
Then


   [ 
statements ] ]


[ 
#Else


   [ 
statements ] ]



#End If

Parts

expression

Required for If and ElseIf statements, optional elsewhere. Any expression, consisting exclusively of one or more conditional compiler constants, literals, and operators, that evaluates to True or False. Three conditional compilation constants are provided: Config, Debug, and Trace. Debug and Trace are Boolean datatypes and can be set in the Project Properties dialogue. When Debug is defined, Debug class methods generate output to the Output window. When it is not defined, Debug class methods are not compiled and no Debug output is generated. Similarly, when Trace is defined, Trace class methods generate output to the Output window. When it is not defined, Trace class methods are not compiled and no Trace output is generated. Config is a string datatype, which corresponds to the current setting in the Configuration Manager.

statements

Required for If statement block, optional elsewhere. Visual Basic program lines or compiler directives that are compiled if the associated expression evaluates to True.

#End If

Terminates the #If statement block.

Remarks

On the surface, the behavior of the #If...Then...#Else directives appears the same as that of the If...Then...Else statements. However, the #If…Then…#Else directives evaluate what is compiled by the compiler, whereas the If…Then…Else statements evaluate conditions at run time.

Conditional compilation is typically used to compile the same program for different platforms. It is also used to prevent debugging code from appearing in an executable file. Code excluded during conditional compilation is completely omitted from the final executable file, so it has no effect on size or performance.

Regardless of the outcome of any evaluation, all expressions are evaluated using Option Compare Text. The Option Compare statement does not affect expressions in #If and #ElseIf statements.

Example

This example uses the #If...Then...#Else construct to determine whether to compile certain statements.

#Const CustomerNumber = 36



#If CustomerNumber = 35 
Then


    ' Insert code to be compiled for customer # 35.



#ElseIf CustomerNumber = 36 
Then


    ' Insert code to be compiled for customer # 36.



#Else


    ' Insert code to be compiled for all other customers.



#End If

See Also

#Const Directive

#Region Directive

Collapses and hides sections of code in Visual Basic .NET files.

#Region 
"
identifier_string
"



#End Region

Parts

identifier_string

Required. String that acts as the title of a region when it is collapsed. Regions are collapsed by default.

#End Region

Terminates the #Region block.

Remarks

The #Region directive lets you specify a block of code that you can expand or collapse when using the outlining feature of the Visual Studio^® Code Editor. #Region statements support block semantics (such as #If...#End If), meaning that the start and end must be in the same code block.

Example

This example uses the #Region directive.

#Region "MathFunctions"


' Insert code for the Math functions here.



#End 
Region

& Operator

Generates a string concatenation of two expressions.

result 
= 
expression1 
& 
expression2

Parts

result

Required. Any String or Object variable.

expression1

Required. Any expression.

expression2

Required. Any expression.

Remarks

If the data type of expression1 or expression2 is not String, it is converted to String. The data type of result is String. If one or both expressions are stated as Nothing or have a value of DBNull.value, they are treated as a string with a value of " ".

Example

This example uses the & operator to force string concatenation. The result is a string value representing the concatenation of the two string operands.

Dim myStr As String


myStr = "Hello" 
& " World"   ' Returns "Hello World".

The following example uses the & operator to force string concatentaion on the result of a database lookup. The result is the string value from the database or an empty string in the case of a null value.

Dim rs As Recordset = Cmd.Execute("Select * from …")


Dim myStr As String


myStr=rs("au_id") & ""

See Also

&= Operator, Concatenation Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality

&= Operator

Concatenates a String expression to a String variable and assigns the result to the variable.

variable 
&= 
expression

Parts

variable

Required. Any String variable.

expression

Required. Any String expression.

Example

The following example uses the &= operator to concatenate two String variables and assign the result to the first variable.

Dim var1 As String = "Hello "


Dim var2 As String = "World!"


var1 
&= var2   ' The value of var1 is now "Hello World!"

See Also

& Operator, *= Operator, += Operator, -= Operator, /= Operator, = Operator, \= Operator, ^= Operator

* Operator

Multiplies two numbers.

number1 
* 
number2

Parts

number1

Required. Any numeric expression.

number2

Required. Any numeric expression.

Result

The result is the product of number1 and number2.

Supported Types

Byte, Short, Integer, Long, Single, Double, Decimal

Remarks

The data type of the result is the same as that of the data type with the greatest range. The order of range, from least to greatest range, is Byte, Short, Integer, Long, Single, Double, and Decimal.

If an expression is stated as Nothing, or is Empty, it is treated as zero.

Example

This example uses the * operator to multiply two numbers. The result is the product of the two operands.

Dim myValue As Double


myValue = 2 
* 2   ' Returns 4.


myValue = 459.35 
* 334.90   ' Returns 153836.315.

See Also

*= Operator, Arithmetic Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality

*= Operator

Multiplies the value of a variable by the value of an expression and assigns the result to the variable.

variable 
*= 
expression

Parts

variable

Required. Any numeric variable.

expression

Required. Any numeric expression.

Example

The following example uses the *= operator to multiply one Integer variable by a second and assign the result to the first variable.

Dim var1 As Integer = 10


Dim var2 As Integer = 3


var1 
*= var2   ' The value of var1 is now 30.

See Also

&= Operator, * Operator, += Operator, -= Operator, /= Operator, = Operator, \= Operator, ^= Operator

+ Operator

Adds two numbers. Also used to concatenate two strings.

expression1 
+ 
expression2

Parts

expression1

Required. Any numeric expression or string.

expression2

Required. Any numeric expression or string.

Result

The value of the result will be the sum of expression1 and expression2 if expression1 and expression2 are numeric or the result of the concatenation of expression1 and expression2 if expression1 and expression2 are strings.

Supported Types

Byte, Short, Integer, Long, Single, Double, Decimal, String

Remarks

When you use the + operator, you may not be able to determine whether addition or string concatenation will occur. Use the & operator for concatenation to eliminate ambiguity and provide self-documenting code.

If neither expression is an Object, the following rules apply:

If one expression is an Object expression, the following rules apply.

If both expressions are Object expressions, the following rules apply (Option Strict Off only):

If one or both expressions are stated as Nothing or have a value of DBNull, they are treated as a string with a value of " ".

Example

This example uses the + operator to add numbers. You can also use the + operator to concatenate strings. However, to eliminate ambiguity, you should use the & operator instead. If the components of an expression created with the + operator are numeric, the arithmetic result is assigned. If the components are exclusively strings, the strings are concatenated. The expression cannot contain components of mixed types. The arithmetic result returns the sum of the two operands. The concatenation result returns a string representing the concatenation of the two operands.

Dim myNumber As Integer


Dim var1 As String


Dim var2 As Integer


myNumber = 2 
+ 2   ' Returns 4.


myNumber = 4257.04 
+ 98112   ' Returns 102369.04.

Option Strict On


' Initialize mixed variables.


var1 = "34"


var2 = 6  


myNumber = var1 
+ var2   ' Generates a compile-time error.





 Option Strict Off


Var1 = "34"


Var2 = 6


myNumber = var1 + var2


' Returns 40 (addition) after the string in var1 is


' converted to a numeric value. Use of Option Strict Off


' for these operations is not recommended.

See Also

& Operator, Concatenation Operators, Arithmetic Operators, Operators Listed by Functionality, Operator Precedence in Visual Basic

+= Operator

Adds the value of an expression to the value of a variable and assigns the result to the variable. Also concatenates a String expression to a String variable and assigns the result to the variable.

variable 
+= 
expression

Parts

variable

Required. Any numeric or String variable.

expression

Required. Any numeric or String expression.

Remarks

This statement will implicitly perform widening but not narrowing conversions if the compilation environment is enforcing strict semantics. If permissive semantics are allowed, the operator will implicitly perform a variety of string and numeric conversions. These conversions are identical to the conversions described for the + operator. For details on how these conversions are performed, see "+ Operator." For more information on strict and permissive semantics, see "Option Strict Statement."

Example

These examples use the += operator to combine the value of one variable with another. In the first example, += is used with numeric variables to add one value to another. In the second example, += is used with String variables to concatenate one value with another. In both cases, the result is assigned to the first variable.

Dim var1 As Integer = 10


Dim var2 As Integer = 3


var1 
+= var2   ' The value of var1 is now 13.

' This example uses string variables.


Dim var1 As String = "10"


Dim var2 As String = "3"


var1 
+= var2   ' The value of var1 is now "103".

See Also

+ Operator, Arithmetic Operators, Concatenation Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality

- Operator

Yields the difference between two numbers or indicates the negative value of a numeric expression.

Syntax 1

expression1 
- 
expression2

Syntax 2

-
number

Parts

number

Required. Any numeric expression.

number1

Required. Any numeric expression.

number2

Required. Any numeric expression.

Result

The result will be the difference between number1 and number2.

Supported Types

Byte, Short, Integer, Long, Single, Double, Decimal

Remarks

In Syntax 1, the - operator is the arithmetic subtraction operator for the difference between two numbers. In Syntax 2, the - operator is the unary negation operator for the negative value of an expression. The data type of the result is the same as that of the data type with the greatest range. The order of range, from least to greatest range, is Byte, Short, Integer, Long, Single, Double, and Decimal.

If an expression is stated as Nothing, it is treated as zero.

Example

This example uses the - operator to calculate and return the difference between two numbers.

Dim myResult As Double


myResult = 4 
- 2   ' Returns 2.


myResult = 459.35 
- 334.90   ' Returns 124.45.

See Also

-= Operator, Arithmetic Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality

-= Operator

Subtracts the value of an expression from the value of a variable and assigns the result to the variable.

variable 
-= 
expression

Parts

variable

Required. Any numeric variable.

expression

Required. Any numeric expression.

Example

The following example uses the -= operator to subtract one Integer variable from another and assign the result to the latter variable.

Dim var1 As Integer = 10


Dim var2 As Integer = 3


var1 
-= var2   ' The value of var1 is now 7.

See Also

&= Operator, *= Operator, += Operator, - Operator, /= Operator, = Operator, \= Operator, ^= Operator

/ Operator

Divides two numbers and returns a floating-point result.

number1 
/ 
number2

Parts

result

Required. Any numeric variable.

number1

Required. Any numeric expression.

number2

Required. Any numeric expression.

Result

The result is the quotient of number1 divided by number2.

Supported Types

Byte, Short, Integer, Long, Single, Double, Decimal

Remarks

The data type of result is usually Double. The following are exceptions to this rule:

If an expression is stated as Nothing, or is Empty, it is treated as zero.

Example

This example uses the / operator to perform floating-point division. The result is the quotient of the two operands.

Dim MyValue As Double


MyValue = 10 
/ 4   ' Returns 2.5.


MyValue = 10 
/ 3   ' Returns 3.333333.

See Also

\= Operator, \ Operator, Arithmetic Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality

/= Operator

Divides the value of a variable by the value of an expression and assigns the result to the variable.

variable 
/= 
expression

Parts

variable

Required. Any numeric variable.

expression

Required. Any numeric expression.

Remarks

This statement assigns a Double to the variable on the left hand side. If Option Strict is On, variable must be a Double. If Option Strict is Off, an implicit conversion will be made and the resultant value assigned to variable, with a possible error at run time. For more information, see "Option Strict Statement."

Example

The following example uses the /= operator to divide one Integer variable by a second and assign the quotient to the first variable.

Dim var1 As Integer = 12


Dim var2 As Integer = 3


var1 
/= var2   ' The value of var1 is now 4.

See Also

&= Operator, *= Operator, += Operator, -= Operator, / Operator, = Operator, \= Operator, ^= Operator

= Operator

Used to assign a value to a variable or property.

variable 
= 
value

Parts

variable

Any variable or any writable property.

value

Any literal, constant, or expression.

Remarks

The name on the left side of the equal sign can be a simple scalar variable, a property, or an element of an array. Properties on the left side of the equal sign can only be those properties that are writable at run time. When used, the value on the right side of the equation is assigned to the variable on the left side of the equation.

Example

This example demonstrates use of the assignment operator. The value on the right side of the expression is assigned to the variable on the left side of the expression.

Dim myInt as Integer


Dim myString as String


Dim myButton as System.Windows.Forms.Button


Dim myObject as Object


myInt = 42


myString = "This is an example of a string literal"


myButton = New System.Windows.Forms.Button()


myObject = myInt


myObject = myString


myObject = myButton

See Also

&= Operator, *= Operator, += Operator, -= Operator, /= Operator, \= Operator, ^= Operator

\ Operator

Divides two numbers and returns an integer result.

number1 
\ 
number2

Parts

number1

Required. Any numeric expression of an integral type.

number2

Required. Any numeric expression of an integral type.

Supported Types

Byte, Short, Integer, or Long

Result

The result is the integer quotient of number1 and number2, dropping the remainder.

Remarks

Before division is performed, any floating-point numeric expressions are coerced to Byte, Short, Integer, or Long expressions if Option Strict is Off. If Option Strict is On, a compiler error results.

The data type of the result is Byte, Short, Integer, or Long. Any fractional portion is truncated.

If any expression is stated as Nothing, or Empty, it is treated as zero. Attempting to perform integer division by zero causes a DivideByZeroExeception to be thrown.

Example

This example uses the \ operator to perform integer division. The result is an integer representing the integer quotient of the two operands.

Dim myValue As Integer


myValue = 11 
\ 4   ' Returns 2.


myValue = 9 
\ 3   ' Returns 3.


myValue = 100 
\ 3   ' Returns 33.


MyValue = 67 
\ -3   ' Returns -22.

See Also

\= Operator, / Operator, Arithmetic Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality

\= Operator

Divides the value of a variable by the value of an expression and assigns the integer result to the variable.

variable 
\= 
expression

Parts

variable

Required. Any numeric variable.

expression

Required. Any numeric expression.

Remarks

For further information on integer division, see "\ Operator."

Example

The following example uses the \= operator to divide one Integer variable by a second and assign the integer result to the first variable.

Dim var1 As Integer = 10


Dim var2 As Integer = 3


var1 
\= var2   ' The value of var1 is now 3.

See Also

&= Operator, *= Operator, += Operator, -= Operator, /= Operator, = Operator, \ Operator, ^= Operator

^ Operator

Raises a number to the power of another number.

Number 
^ 
exponent

Parts

number

Required. Any numeric expression.

exponent

Required. Any numeric expression.

Result

The result value will be number raised to the exponent power.

Supported Types

Double. All operands of a different type will be converted to Double.

Remarks

Number can be negative only if exponent is an integer value. When more than one exponentiation is performed in a single expression, the ^ operator is evaluated as it is encountered from left to right.

Usually, the data type of result is Double.

Example

This example uses the ^ operator to raise a number to the power of an exponent. The result is the first operand raised to the power of the second.

Dim myValue As Double


myValue = 2 
^ 2   ' Returns 4.


myValue = 3 
^ 3 
^ 3   ' Returns 19683.


myValue = (-5) 
^ 3   ' Returns -125.


myValue = (-5) ^ 4   ' Returns 625.

See Also

^= Operator, Arithmetic Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality

^= Operator

Raises the value of a variable to the power of an expression and assigns the result back to the variable.

variable 
^= 
expression

Parts

variable

Required. Any numeric variable.

expression

Required. Any numeric expression.

Example

The following example uses the ^= operator to raise the value of one Integer variable to the power of a second variable and assign the result to the first variable.

Dim var1 As Integer = 10


Dim var2 As Integer = 3


var1 
^= var2   ' The value of var1 is now 1000.

See Also

&= Operator, *= Operator, += Operator, -= Operator, /= Operator, = Operator, \= Operator, ^ Operator

Add Method

Adds a member to a Collection object.

Public Sub Add( _


 
  ByVal 
Item 
As Object, _


 
  Optional ByVal 
Key 
As String, _


 
  Optional ByVal { 
Before | After } 
As Object = Nothing _



)

Parameters

Item

Required. An object of any type that specifies the member to add to the collection.

Key

Optional. A unique String expression that specifies a key string that can be used instead of a positional index to access a member of the collection.

Before

Optional. An expression that specifies a relative position in the collection. The member to be added is placed in the collection before the member identified by the Before argument. If Before is a numeric expression, it must be a number from 1 to the value of the collection's Count property. If Before is a String expression, it must correspond to the key string specified when the member being referred to was added to the collection. You cannot specify both Before and After.

After

Optional. An expression that specifies a relative position in the collection. The member to be added is placed in the collection after the member identified by the After argument. If After is a numeric expression, it must be a number from 1 to the value of the collection's Count property. If After is a String expression, it must correspond to the key string specified when the member referred to was added to the collection. You cannot specify both Before and After.

Exceptions/Error Codes

Remarks

The Before or After argument must refer to an existing member of the collection; otherwise, an error occurs.

An error also occurs if a specified Key value matches the key for an existing member of the collection.

Example

This example uses the Add method to add Child objects—instances of a class called Child containing a Public property Name—to a collection called Family. To see how this works, create a Form with two Buttons and set their Text properties to Add and List. Add the Child class definition and the Family declaration to the form code. Modify the Click events for the Add and List buttons as shown. The Add button allows you to add children. The List button will display the names of all the children.

Public Class Child


   Public Name As String


   Sub New(ByVal newName As String)


      Name = newName


   End Sub


End Class

Private family As New Collection() ' Create a Collection object.

Private Sub Add_Click(ByVal sender As System.Object, _


ByVal e As System.EventArgs) Handles Button1.Click


   Dim newName As String


   newName = InputBox("Name of new family member: ")


   If newName <> "" Then


      family.
Add(New Child(newName), newName
)


   End If


End Sub

Private Sub List_Click(ByVal sender As System.Object, _


ByVal e As System.EventArgs) Handles Button2.Click


   Dim aChild As Child


   For Each aChild In family


      MsgBox(aChild.Name)


   Next


End Sub

See Also

Item Property, Remove Method, ArgumentException

Applies To

Collection Object

AddHandler Statement

Associates an event with an event handler.

AddHandler 
event, 
AddressOf 
eventhandler

Parts

event

The name of the event to handle.

eventhandler

The name of a procedure that will handle the event.

Remarks

The AddHandler and RemoveHandler statements allow you to start and stop event handling at any time during program execution.

Example

Sub TestEvents()


   Dim Obj As New Class1()


   ' Associate an event handler with an event.


   AddHandler Obj.Ev_Event, AddressOf EventHandler


   Obj.CauseSomeEvent()   ' Ask the object to raise an event.


End Sub

Sub EventHandler()


   ' This procedure handles events raised by the object Obj.


   MsgBox("EventHandler caught event.")   ' Handle the event.


End Sub

Public Class Class1


   Public Event Ev_Event()   ' Declare an event.


   Sub CauseSomeEvent()


      RaiseEvent Ev_Event()   ' Raise an event.


   End Sub


End Class

See Also

RemoveHandler Statement, Handles

AddressOf Operator

Creates a procedure delegate instance that references the specific procedure.

AddressOf procedurename

The required procedurename specifies the procedure that will be referenced by the newly created procedure delegate.

Remarks

The AddressOf operator creates a function delegate that points to the function specified by procedurename. When the specified procedure is an instance method then the function delegate refers to both the instance and the method so that when the function delegate is invoked the specified method of the specified instance is called.

The AddressOf operator can be used as the operand of a delegate constructor or it can be used in a context in which the type of the delegate can be determined by the compiler.

Example

This example uses the AddressOf operator to designate a delegate to handle the Click event of a button.

Public Sub ButtonClickHandler(ByVal sender As Object, e As _


   System.EventArgs)


' Implementation code omitted.


End Sub

Public Sub New()


   AddHandler Button1.Click, 
AddressOf ButtonClickHandler


   ' Additional code omitted.


End Sub

The following example uses the AddressOf operator to designate the startup function for a thread.

Public Sub CountSheep()


   Dim i As Integer = 1 ' Sheep don't count from 0.


   Do While (True) ' Endless loop.


      Console.WriteLine("Sheep " & i & " Baah")


      i = i + 1


      Thread.Sleep(1000) 'Wait 1 second.


   Loop


End Sub

Sub UseThread()


   Dim t As New System.Threading.Thread(
AddressOf CountSheep)


   t.Start()


End Sub

See Also

Declare Statement, Function Statement, Sub Statement

Alias

The Alias keyword indicates that an external procedure has another name in its DLL.

The Alias keyword is used in this context:

Declare Statement

See Also

Visual Basic Language Keywords

And Operator

Performs a logical conjunction on two Boolean expressions, or bitwise conjunction on two numeric expressions.

result 
= 
expression1 
And 
expression2

Parts

result

Required. Any Boolean or numeric expression. The result for Boolean comparison is the Boolean result of comparison of the two expressions. The result for numeric comparison is a numeric value resulting from the bitwise conjunction of two numeric expressions

expression1

Required. Any Boolean or numeric expression.

expression2

Required. Any Boolean or numeric expression.

Remarks

For Boolean comparison, if both expression1 and expression2 evaluate to True, result is True. If expression1 evaluates to True and expression2 evaluates to False, result is False. If expression1 evaluates to False, and expression2 evaluates to True, the result is False. The following table illustrates how result is determined:

When applied to numeric values, the And operator performs a bitwise comparison of identically positioned bits in two numeric expressions and sets the corresponding bit in result according to the following table:

If the operands consist of one Boolean expression and one numeric expression, the result Boolean expression will be converted to a numeric value (–1 for True, and 0 for False) and the bitwise operation will result.

Example

This example uses the And operator to perform a logical conjunction on two expressions. The result is a Boolean value that represents whether the entire conjoined expression is true.

Dim A As Integer = 10


Dim B As Integer = 8


Dim C As Integer = 6


Dim myCheck As Boolean


myCheck = A > B 
And B > C   ' Returns True.


myCheck = B > A 
And B > C   ' Returns False.

This example uses the And operator to perform logical conjunction of the individual bits of two numeric expressions. The bit in the result pattern is set if the corresponding bits in the operands are both set.

Dim A As Integer = 10


Dim B As Integer = 8


Dim C As Integer = 6


Dim myCheck As Integer


myCheck = (A 
And B)   ' Returns 8.


myCheck = (A 
And C)   ' Returns 2.


myCheck = (B 
And C)   ' Returns 0.

See Also

Logical/Bitwise Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality, AndAlso Operator, Logical Operators

AndAlso Operator

Performs short-circuiting logical conjunction on two expressions.

result 
= 
expression1 
AndAlso 
expression2

Parts

result

Required. Any Boolean expression. The result is the Boolean result of comparison of the two expressions.

expression1

Required. Any Boolean expression.

expression2

Required. Any Boolean expression.

Remarks

If both expression1 and expression2 evaluate to True, result is True. If expression1 evaluates to True and expression2 evaluates to False, result is False. If expression1 evaluates to False, expression2 is not evaluated, and result is False (the operator is said to have short-circuited the expression). The following table illustrates how result is determined:

Example

This example uses the AndAlso operator to perform a logical conjunction on two expressions. The result is a Boolean value that represents whether the entire conjoined expression is true. If the first expression is False, the second is not evaluated.

Dim A As Integer = 10


Dim B As Integer = 8


Dim C As Integer = 6


Dim myCheck As Boolean


myCheck = A > B 
AndAlso B > C   ' True.


myCheck = B > A 
AndAlso B > C   ' False. Second expression not evaluated.


myCheck = A > B 
AndAlso C > B   ' False. Second expression evaluated.

' This example demonstrates using the AndAlso operator to search through


' array values. If i is greater than the upper bound of the array, it does


' attempt to find a corresponding value in the array.

Dim i As Integer = 0


While i <= UBound(arr) 
AndAlso arr(i) <> SearchValue


   i += 1


End While

See Also

Logical/Bitwise Operators, Operator Precedence in Visual Basic, Operators Listed by Functionality, Logical Operators

Ansi

The Ansi keyword indicates that strings are converted to American National Standards Institute (ANSI) values regardless of the name of the method being declared.

The Ansi keyword is used in this context:

Declare Statement

See Also

Visual Basic Language Keywords

AppActivate Function

Activates an application window.

Public Overloads Sub AppActivate( _


 
  ByVal { 
Title 
As String | 
ProcessID 
As Integer } 
_



)

Parameters

Title

String expression specifying the title in the title bar of the application window you want to activate. You can use the task ID returned by the Shell function.

ProcessID

Integer specifying the Win32^® Process ID number assigned to this process.

Exceptions/Errors

Remarks

The AppActivate function changes the focus to the named application or window, but does not affect whether it is maximized or minimized. Focus moves from the activated application window when the user takes some action to change the focus or close the window. Use the Shell function to start an application and set the window style.

You can use AppActivate only with processes that own windows. Most console applications do not own windows, which means that they do not appear in the list of processes that AppActivate searches. When running from a console application, the system creates a separate process to run the application and returns the output to the console process. Consequently, when the current Process ID is requested, you get the created process's Process ID rather than the console application's Process ID.

At run time the AppActivate function activates any running application whose title matches Title or whose Process ID matches ProcessID. If there is no exact match, it activates any application whose title string begins with Title. If there is more than one application named by Title, the AppActivate function activates one at random.

Example

This example illustrates various uses of the AppActivate function to activate an application window. The Shell procedures assume the applications are in the paths specified.

Dim notepadID As Integer


' Activate a running notepad process.



AppActivate("Untitled - Notepad"
)


' AppActivate can also use the return value of the Shell function.


' Shell runs a new instance of notepad.


notepadID = Shell("C:\WINNT\NOTEPAD.EXE", AppWinStyle.MinimizedNoFocus)


' Activate the new instance of notepad. 



AppActivate(notepadID
)

See Also

Shell Function

AppWinStyle Enumeration

When you issue Shell commands, you can use the following enumeration members in your code in place of the actual values.

AppWinStyle Enumeration Members

The Style argument takes the following AppWinStyle enumeration members:

See Also

Shell Function

As

The As keyword introduces an As clause, which identifies a data type.

The As keyword is used in these contexts:

Const Statement

Declare Statement

Delegate Statement

Dim Statement

Enum Statement

Event Statement

Function Statement

Property Statement

Sub Statement

Try...Catch...Finally Statements

See Also

Visual Basic Language Keywords

Asc, AscW Functions

Returns an Integer value representing the character code corresponding to a character.

Public Overloads Function Asc(ByVal 
String 
As Char) As Integer



Public Overloads Function AscW(ByVal 
String 
As Char) As Integer

-or-

Public Overloads Function Asc(ByVal 
String 
As String) As Integer



Public Overloads Function AscW(ByVal 
String 
As String) As Integer

Parameter

String

Required. Any valid Char or String expression. If String is a String expression, only the first character of the string is used for input. If String is Nothing or contains no characters, an ArgumentException error occurs.

Exceptions/Errors

Remarks

Asc returns the code point, or character code, for the input character. This can be 0 through 255 for single-byte character set (SBCS) values and –32768 through 32767 for double-byte character set (DBCS) values. The returned value depends on the code page for the current thread, which is contained in the ANSICodePage property of the TextInfo class. TextInfo.ANSICodePage can be obtained by specifying System.Globalization.CultureInfo.CurrentCulture.TextInfo.ANSICodePage.

AscW returns the Unicode code point for the input character. This can be 0 through 65535. The returned value is independent of the culture and code page settings for the current thread.

Example

This example uses the Asc function to return Integer character codes corresponding to the first letter in each string.

Dim MyInt As Integer


MyInt = 
Asc("A"
)   ' MyInt is set to 65.


MyInt = 
Asc("a"
)   ' MyInt is set to 97.


MyInt = 
Asc("Apple"
)   ' MyInt is set to 65.

See Also

Chr, ChrW Functions; Conversion Functions; Type Conversion Functions

Assembly

The Assembly keyword indicates that an attribute block at the beginning of a source file applies to the entire assembly and not only to the current module.

Auto

The Auto keyword indicates that strings are converted according to common language runtime rules based on the name of the method being declared.

The Auto keyword is used in this context:

Declare Statement

See Also

Visual Basic Language Keywords

Beep Function

Sounds a tone through the computer's speaker.

Public Sub Beep()

Remarks

The pitch and duration of the beep depend on your hardware and system software, and therefore vary among computers.

Example

This example uses the Beep function to sound a long, uninterrupted tone through the computer's speaker.

Dim I As Integer


For I = 1 To 100   ' Loop 100 times.


   
Beep   ' Sound a tone.


Next I

See Also

Visual Basic Run-Time Library Members

Boolean Data Type

Boolean variables are stored as 16-bit (2-byte) numbers, but they can only be True or False. Use the keywords True and False to assign one of the two states to Boolean variables.

When numeric data types are converted to Boolean values, 0 becomes False and all other values become True. When Boolean values are converted to numeric types, False becomes 0 and True becomes –1.

The equivalent .NET data type is System.Boolean.

See Also

Data Type Summary, Integer Data Type, Type Conversion Functions, Conversion Summary

ByRef

The ByRef keyword indicates that an argument is passed in such a way that the called procedure can change the value of a variable underlying the argument in the calling code.

The ByRef keyword is used in these contexts:

Declare Statement

Function Statement

Sub Statement

See Also

Visual Basic Language Keywords

Byte Data Type

Byte variables are stored as unsigned 8-bit (1-byte) numbers ranging in value from 0 through 255.

The Byte data type is used for containing binary data.

The equivalent .NET data type is System.Byte.

See Also

Data Type Summary, Integer Data Type, Short Data Type, Type Conversion Functions, Conversion Summary

ByVal

The ByVal keyword indicates that an argument is passed in such a way that the called procedure or property cannot change the value of a variable underlying the argument in the calling code.

The ByVal keyword is used in these contexts:

Declare Statement

Function Statement

Property Statement

Sub Statement

See Also

Visual Basic Language Keywords