Function procedures (Visual Basic)
Function procedure is a series of Visual Basic statements enclosed by the
End Function statements. The
Function procedure performs a task and then returns control to the calling code. When it returns control, it also returns a value to the calling code.
Each time the procedure is called, its statements run, starting with the first executable statement after the
Function statement and ending with the first
Exit Function, or
Return statement encountered.
You can define a
Function procedure in a module, class, or structure. It is
Public by default, which means you can call it from anywhere in your application that has access to the module, class, or structure in which you defined it.
Function procedure can take arguments, such as constants, variables, or expressions, which are passed to it by the calling code.
The syntax for declaring a
Function procedure is as follows:
[Modifiers] Function FunctionName [(ParameterList)] As ReturnType [Statements] End Function
The modifiers can specify access level and information regarding overloading, overriding, sharing, and shadowing. For more information, see Function Statement.
You declare each parameter the same way you do for Sub Procedures.
Function procedure has a data type, just as every variable does. This data type is specified by the
As clause in the
Function statement, and it determines the data type of the value the function returns to the calling code. The following sample declarations illustrate this.
Function Yesterday() As Date End Function Function FindSqrt(radicand As Single) As Single End Function
For more information, see "Parts" in Function Statement.
The value a
Function procedure sends back to the calling code is called its return value. The procedure returns this value in one of two ways:
It uses the
Returnstatement to specify the return value, and returns control immediately to the calling program. The following example illustrates this.
Function FunctionName [(ParameterList)] As ReturnType ' The following statement immediately transfers control back ' to the calling code and returns the value of Expression. Return Expression End Function
It assigns a value to its own function name in one or more statements of the procedure. Control does not return to the calling program until an
End Functionstatement is executed. The following example illustrates this.
Function FunctionName [(ParameterList)] As ReturnType ' The following statement does not transfer control back to the calling code. FunctionName = Expression ' When control returns to the calling code, Expression is the return value. End Function
The advantage of assigning the return value to the function name is that control does not return from the procedure until it encounters an
Exit Function or
End Function statement. This allows you to assign a preliminary value and adjust it later if necessary.
You invoke a
Function procedure by including its name and arguments either on the right side of an assignment statement or in an expression. You must provide values for all arguments that are not optional, and you must enclose the argument list in parentheses. If no arguments are supplied, you can optionally omit the parentheses.
The syntax for a call to a
Function procedure is as follows.
If (( functionname
)] / 3) <= expression
When you call a
Function procedure, you do not have to use its return value. If you do not, all the actions of the function are performed, but the return value is ignored. MsgBox is often called in this manner.
Illustration of declaration and call
Function procedure calculates the longest side, or hypotenuse, of a right triangle, given the values for the other two sides.
Function Hypotenuse(side1 As Double, side2 As Double) As Double Return Math.Sqrt((side1 ^ 2) + (side2 ^ 2)) End Function
The following example shows a typical call to
Dim testLength, testHypotenuse As Double testHypotenuse = Hypotenuse(testLength, 10.7)
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