Commodore CBM - User-Defined Function; Def Fn

Format:
USR(arg)
where:
arg
is the parameter value passed to the subroutine.
The USR function is described in more detail in Chapter 6.
USER-DEFINED FUNCTION
DEF FN
The DEF function (DEF FN) allows the user to define his own special purpose
functions and use the functions
in his program in the same way that the intrinsic
PET BASIC functions are used.
Format:
DEF FN name(arg)=formula
where:
Define user function.
arg
name
formula
is a simple floating point variable name one or
two characters in length. The name can be
longer. but an alphabetic na me of more thao.-
five letter_s yields a syntax error. The function is
used in the program by referring to the name
FNname.
is a simple floating point variable name. This is
a dummy assignment that represents the argu-
ment value in the formula
ta the right. A string
($) or integer (%) arg is not allowed.
is any arithmetic expression containing any
combination of numeric constants. variables.
and operators. Normally the arg appears in the
formula.
A user-defined function
is limited to one SO-character line: however. a pre-
viously defined function can be used in the formula in another user-defined func-
tion.
so user-defined functions of any desired complexity can be developed.
A user-defined function is used by typing in the function name. FNname.
followed by the actual argument enclosed in parentheses.
FNname(arg) Reference user function.
Onlya single argument can be passed ta a user-defined function. The func-
tion name can
be redefined by another DEF FN with the same name in the same
program.
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