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84 lines
2.8 KiB
Plaintext
84 lines
2.8 KiB
Plaintext
'''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.'''
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----
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The '''DEF FN''' statement defines a non-recursive function in the main module that can use the module's variable values.
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{{PageSyntax}}
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:[[DEF FN]]{{Parameter|name}} [({{Parameter|parameterList}})] = {{Parameter|expression}}
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::or,
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:[[DEF FN]]{{Parameter|name}} [({{Parameter|parameterList}})]
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::[{{Parameter|statements}}]
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::[[DEF FN|FN]]{{Parameter|name}} = {{Parameter|expression}}
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::[{{Parameter|statements}}]
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:'''END DEF'''
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{{PageDescription}}
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*'''[[Keywords currently not supported by QB64|Not supported in QB64.]]'''
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* {{Parameter|name}} is the name of the function.
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* {{Parameter|parameterList}} is a comma-separated list of one or more parameters, similar to [[SUB]] and [[FUNCTION]] statements.
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* {{Parameter|expression}} is any numerical or string value to return from the function.
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* Function can be created anywhere in a module. Not in [[SUB]] procedures.
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* Function must be defined only once and the definition cannot be in recursive (repeated) parts of a program.
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* Function returns should be assigned to a variable when an alteration to the return value is necessary.
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* Function references should only be made after the declaration.
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* Multi-line function definitions must end with '''END DEF'''.
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* To leave a DEF Fn function early use '''EXIT DEF'''.
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* This type of function can share values in module level code. To keep values local to the procedure use [[STATIC]].
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* Parameters cannot be from arrays, records or fixed length strings.
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* ''Fn'' must prefix the function name inside of the procedure and in a call.
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==QBasic/QuickBASIC==
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* Other variable names or procedures cannot begin with FN or fn in QBasic.
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* QBasic Help recommends creating real [[FUNCTION]]s over DEF FN functions because of the above limitations.
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{{PageExamples}}
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:Function to get the base 10 logarithm of a number value.
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{{CodeStart}}{{Cl|DEF FN}}Log10#(x) = {{Cl|LOG}}(x) / {{Cl|LOG}}(10.#)
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{{Cl|PRINT}} FNLog10#(10)
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{{Cl|PRINT}} FNLog10#(100)
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{{Cl|PRINT}} FNLog10#(1000)
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{{CodeEnd}}
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{{OutputStart}} 1
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2
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3
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{{OutputEnd}}
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:Demonstrates the multi-line syntax by drawing a circle:
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{{CodeStart}}{{Cl|CONST}} PI# = 3.141592653589793#
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{{Cl|DEF FN}}DegreesToRadians# (degrees#)
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radians# = degrees# * (PI# / 180#)
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FNDegreesToRadians# = radians#
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{{Cl|DEF FN|END DEF}}
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{{Cl|SCREEN}} 13
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{{Cl|WINDOW}} (-1, -1)-(1, 1)
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{{Cl|CLS}}
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{{Cl|FOR}} degree% = 0 TO 360
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x# = {{Cl|COS}}(FNDegreesToRadians#(degree%))
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y# = {{Cl|SIN}}(FNDegreesToRadians#(degree%))
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{{Cl|PSET}} (x#, y#)
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{{Cl|NEXT}} degree%
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{{CodeEnd}}
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{{PageSeeAlso}}
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* [[FUNCTION]], [[SUB]]
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* [[DEFSTR]], [[DEFINT]]
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* [[DEFSNG]], [[DEFLNG]]
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* [[DEFDBL]]
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* [[_DEFINE]]
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{{PageNavigation}} |