Program Structure and Flow | VB.NET Language Pocket Reference

1.25 Program Structure and Flow

Call Statement

[Call] procedurename[(argumentlist)]

procedurename required; n/a

The name of the subroutine being called

argumentlist optional; any

A comma-delimited list of arguments to pass to the subroutine being called

Description

Passes execution control to a procedure, function, or DLL procedure or function.

CallByName Function

Microsoft.VisualBasic.Interaction

CallByName(Object, ProcName, UseCallType, Args(  ))

Object required; Object

A reference to the object containing the procedure being called.

ProcName required; String

The name of the procedure to call.

UseCallType required; CallType constant

A constant of type CallType indicating what type of procedure is being called. The CallType constants are:

Constant	Value	Description
`Method`	1	The called procedure is a method
`Get`	2	The called procedure retrieves a property value
`Let`	4	The called procedure sets the value of a property

Args optional; any

A ParamArray argument representing the arguments required by the procedure being called.

Named Arguments

Yes, if Args( ) is omitted

Return Value

Depends on the return value (if any) of the called procedure

Description

Provides a method for calling a class member by name.

Since ProcName is a string expression, rather than the literal name of a routine, it is possible to call routines dynamically at runtime using a string variable to hold the various procedure names.

Do...Loop Statement

Do [{While | Until} condition]  Syntax 1.

  [statements]

[Exit Do]

  [statements]

Loop

Do  Syntax 2.

  [statements]

[Exit Do]

  [statements]

Loop [{While | Until} condition]

condition optional; Boolean expression

An expression that evaluates to True or False

statements optional

Program statements that are repeatedly executed while, or until, condition is True

Description

Repeatedly executes a block of code while or until a condition becomes True.

End... Statement

End

End Class

End Enum

End Function

End Get

End If

End Interface

End Module

End Namespace

End Property

End Select

End Set

End Structure

End Sub

End SyncLock

End Try

End With

End While

Description

Ends a procedure or a block of code.

Exit . . . Statement

Exit Do

Exit For

Exit Function

Exit Property

Exit Select

Exit Sub

Exit Try

Exit While

Description

Prematurely exits a block of code.

For . . . Next Statement

For counter = initial_value To maximum_value _

  [Step stepcounter]

 'code to execute on each iteration

  [Exit For]

Next [counter]

counter required (optional with Next statement); any valid numeric variable

A variable that serves as the loop counter

initial_value required; any valid numeric expression

The starting value of counter for the first iteration of the loop

maximum_value required; any valid numeric expression

The value of counter during the last iteration of the loop

stepcounter optional (required if Step is used); any valid numeric expression

The amount by which counter is to be incremented or decremented on each iteration of the loop

Description

Defines a loop that executes a given number of times, as determined by a loop counter.

To use the For...Next loop, you must assign a numeric value to a counter variable. This counter is either incremented or decremented automatically with each iteration of the loop. In the For statement, you specify the value that is to be assigned to the counter initially and the maximum value the counter will reach for the block of code to be executed. The Next statement marks the end of the block of code that is to execute repeatedly, and it also serves as a kind of flag that indicates that the counter variable is to be modified.

For Each...Next Statement

For Each element In group

[statements]

[Exit For]

[statements]

Next [element]

element required; Object or any user-defined object type

An object variable to which the current element from the group is assigned

group required

An object collection or array

statements optional

A line or lines of program code to execute within the loop

Description

Loops through the items of a collection or the elements of an array.

GoTo Statement

GoTo label

label required; string literal

A subroutine name

Description

Passes execution to a specified line within a procedure.

If...Then...Else Statement

Standard syntax:

If condition Then

  [statements]

[ElseIf condition-n Then

  [elseifstatements] ...

[Else

  [elsestatements]]

End If

One-line syntax:

If condition Then [statements] [Else elsestatements]

condition required; Boolean

An expression returning either True or False or an object type

statements optional

Program code to be executed if condition is true

condition-n optional

Same as condition

elseifstatements optional

Program code to be executed if the corresponding condition-n is True

elsestatements optional

Program code to be executed if the corresponding condition or condition-n is False

Description

Executes a statement or block of statements based on the Boolean (True or False) value of an expression.

Return Statement

Return  In a subroutine

Return ReturnValue  In a function

ReturnValue required; any

The return value of the function

Description

Returns to the calling program from a subroutine or function.

Select Case Statement

Select Case testexpression

  [Case expressionlist-n

  [statements-n]] ...

  [Case Else

  [elsestatements]]

End Select

testexpression required; any

Any numeric or string expression whose value determines which block of code is executed.

expressionlist-n required; any

Comma-delimited list of expressions to compare values with testexpression

statements-n optional

Program statements to execute if a match is found between any section of expressionlist and testexpression

elsestatements optional

Program statements to execute if a match between testexpression and any expressionlist cannot be found

expressionlist can use any (or a combination of any) of the following:

expressionlist syntax	Examples
`expression`	iVar - iAnotherVar iVar
`expression` To `expression`	5 To 10 8 To 11, 13 to 15 "A" To "D"
Is `comparisonoperator` `expression`	Is = 10

Description

Allows for conditional execution of a block of code, typically out of three or more code blocks, based on some condition. Use the Select Case statement as an alternative to complex nested If...Then...Else statements.

Stop Statement

Stop

Description

Suspends program execution.

While...End While Statement

While condition

  [statements]

[Exit While]

[statements]

End While

condition required; Numeric or String

An expression evaluating to True or False

statements optional

Program statements to execute while condition remains True

ExitWhile optional; Keyword

Exits the While loop

Description

Repeatedly executes program code while a given condition remains True.