Texas Instruments TI-99/4A - Page 126

DEF
The parameter used in the DEF statement is local to the DEF
statement in which it is used. This means that it is riistinr.t fmm any
variable with the same name which is used in other statements in
the program.
Thus, evaluating the function does not affect the value
of
a variahlF. whir.h h;l~ thp ~;lmp n;lmp. as the paramf"tf"r
A DEF statement is only performed when the function it defines is
rd~r~nr.f'ri in 'In f'xprpssion When the computer encounters a DEF
statement while running a program. it takes no action but proceeds
to the next statement. A DEF statement may appear anywhere in a
program and need not logically precede a reference to the function.
but the function definition must have a lower line number than any
statement which references the function. A DEF statement can
reference other defined functions (line 170).
In a DEF statement, the function you specify may not reference
itself either directly (e.g. DEF B =B*2) or indirectly (e.g. DEF
F=G; DEF G - F).The pa.ramctcrYou specify may not bc uscd as
an array. You can use an array element in a function definition as
long as
the array does not have the same name as the parameter.
11,106
Examples:
>NEOI
>100 DEF FUNC(A}=A*(A+B-5)
>110
A=6.9
>120 B"13
>130 PRINT "6= ";B:"FUNCC3}"
"iFUNC(3):"A= ";A
>140 END
>RUN
6= 13
FUNC(3)= 33
A= 6.9
** DONE **
>NEW
>100 REM FIND t' (Xl USING
NUMERICAL APPROXIMATION
>110 INPUT OX;? ":X
>120 IF ABS<X».01 THEN 150
>130 H;.oooo1
>140 GOTO 180
>150 H=.OQ1*AB$(X)
>160
DEF F(z)=3*Z
A
3-2*Z+1
>170 DEF DER(X)=(F(X+H)-F(X-H
})/(2*H)
>180 PRINT "F'{"iSTR$(X);")=
"iDER(X)
>190 END
>RUN
X=? .1
F
'
(.1}= -1.90999997
** DONE **
>NEW
>100 DEF GX(X)=GX(Z>*X
>110
PRINT GXO)
>120 END
>RUN
W MEMORY FULL iN 110
>100 DEF GX(A)=A(3)A2
>RUN
* NAME CONFLICT IN 100
User's Reference Guide