User Guide : Scripting : Script Statements : Function Statement
 
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Function Statement
 
Description
Declares the name, arguments, and code that form the body of a function procedure.
Syntax
Function functionname [(argumentlist)]
[statementblock]
[functionname = expression]
[Return]
[statementblock]
[functionname = expression]
End Function
Arguments
functionname - Name of the function. Function procedure names follow the same naming conventions as other variables and can include a type-declaration character. Functionname cannot be the same as any other globally recognized name in the program. Such names include the names of procedures (in Basic or a dynamic-link library [DLL]), Private variables, and Global constants.
argumentlist - List of variables, representing arguments, that are passed to the function procedure when it is called. Multiple variables are separated by commas.
The argument argument list has the following syntax:
variable[( )] [,variable[( )]] . . .
variable - Name of the variable representing the argument within argumentlist. For array variables, use the parentheses but omit the number of dimensions.
statementblock - Any group of statements that are to be executed within the body of the function procedure.
expression - Return value of the function. A function procedure returns a value by assigning that value to the function functionname. Any number of such assignments can be used anywhere within the procedure. If no value is assigned to functionname, the procedure returns a default value: A numeric function returns 0, a String function returns a zero-length string (""), and a Variant function returns Empty.
Return - The Return statement causes the immediate termination of the function (See Return Statement.) Program execution resumes with the statement after the calling statement.
Remarks
All executable code must be in Function procedures. You cannot define a function procedure inside another Function procedure.
Function and End Function mark the beginning and end of a function procedure, respectively.
You can call a function procedure by using the function name, followed by the argument list in parentheses, in an expression. If the function has no arguments, you still must include the parentheses.
Variables used in Function procedures fall into two categories: those that are explicitly declared within the procedure and those that are not. Variables that are explicitly declared in a procedure (using Dim or an equivalent) are always local to the procedure. Other variables used but not explicitly declared in a procedure are also local unless they are explicitly declared at some higher level outside the procedure.
A procedure can use a variable that is not explicitly declared in the procedure, but a name conflict can occur if anything you have defined in the Declarations section has the same name. If your procedure refers to an undeclared variable that has the same name as another procedure, a Private-level constant or variable, or an object, Basic assumes that your procedure is referring to that Private-level name. Explicitly declare variables to avoid this kind of conflict. You can use an Option Explicit statement to force explicit declaration of variables. See Option Evaluate Automatic Statement.
Caution!  Function procedures can be recursive; that is, they can call themselves to perform a given task. However, recursion can lead to stack overflow. In addition, there is a 32 parameter limitation in functions, and if this limitation is exceeded, stack overflow occurs. For more information, see Stack Overflow.
Example
To return a value from a function, assign the value to the function name. For example, in a function named BinarySearch, you could assign the value of the constant False to the name to indicate that the value was not found:
Function BinarySearch(...)
  ...
  ' Value not found. Return a value of False.
  If lower > upper Then
    BinarySearch = False
    Return
  End If
End Function