'''This page is maintained for historic purposes. The keyword is not supported in QB64. Create functions using [[FUNCTION]]. If older code contains ''DEF FN'' functions, they must be adapted to be compiled with QB64.'''


----


The '''DEF FN''' statement defines a non-recursive function in the main module that can use the module's variable values.


{{PageSyntax}}
:[[DEF FN]]{{Parameter|name}} [({{Parameter|parameterList}})] = {{Parameter|expression}}
::or,
:[[DEF FN]]{{Parameter|name}} [({{Parameter|parameterList}})]
::[{{Parameter|statements}}]
::[[DEF FN|FN]]{{Parameter|name}} = {{Parameter|expression}}
::[{{Parameter|statements}}]
:'''END DEF'''


{{PageDescription}}
*'''[[Keywords currently not supported by QB64|Not supported in QB64.]]'''
* {{Parameter|name}} is the name of the function.
* {{Parameter|parameterList}} is a comma-separated list of one or more parameters, similar to [[SUB]] and [[FUNCTION]] statements.
* {{Parameter|expression}} is any numerical or string value to return from the function.
* Function can be created anywhere in a module. Not in [[SUB]] procedures.
* Function must be defined only once and the definition cannot be in recursive (repeated) parts of a program.
* Function returns should be assigned to a variable when an alteration to the return value is necessary.
* Function references should only be made after the declaration.
* Multi-line function definitions must end with '''END DEF'''.
* To leave a DEF Fn function early use '''EXIT DEF'''.
* This type of function can share values in module level code. To keep values local to the procedure use [[STATIC]].
* Parameters cannot be from arrays, records or fixed length strings.
* ''Fn'' must prefix the function name inside of the procedure and in a call.


==QBasic/QuickBASIC==
* Other variable names or procedures cannot begin with FN or fn in QBasic.
* QBasic Help recommends creating real [[FUNCTION]]s over DEF FN functions because of the above limitations.


{{PageExamples}}
:Function to get the base 10 logarithm of a number value.
{{CodeStart}}{{Cl|DEF FN}}Log10#(x) = {{Cl|LOG}}(x) / {{Cl|LOG}}(10.#)

{{Cl|PRINT}} FNLog10#(10)
{{Cl|PRINT}} FNLog10#(100)
{{Cl|PRINT}} FNLog10#(1000)
{{CodeEnd}}
{{OutputStart}} 1
 2
 3
{{OutputEnd}}


:Demonstrates the multi-line syntax by drawing a circle:
{{CodeStart}}{{Cl|CONST}} PI# = 3.141592653589793#

{{Cl|DEF FN}}DegreesToRadians# (degrees#)
    radians# = degrees# * (PI# / 180#)
    FNDegreesToRadians# = radians#
{{Cl|DEF FN|END DEF}}

{{Cl|SCREEN}} 13
{{Cl|WINDOW}} (-1, -1)-(1, 1)
{{Cl|CLS}}

{{Cl|FOR}} degree% = 0 TO 360
    x# = {{Cl|COS}}(FNDegreesToRadians#(degree%))
    y# = {{Cl|SIN}}(FNDegreesToRadians#(degree%))
    {{Cl|PSET}} (x#, y#)
{{Cl|NEXT}} degree%

{{CodeEnd}}


{{PageSeeAlso}}
* [[FUNCTION]], [[SUB]]
* [[DEFSTR]], [[DEFINT]]
* [[DEFSNG]], [[DEFLNG]]
* [[DEFDBL]]
* [[_DEFINE]]


{{PageNavigation}}