Sharp PC-1500 - Page 98

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G. DEBUGGING
No matter h ovv careful you arc, eventually you wi ll create a program wh ich does not do quite
wha t you expec t it to . In order to iso la te th e p ro ble m, SHARP's designers ha ve provided a s pec ial
method of execut i ng pro grams known as th e "T r ace" mode . In t he Tr ace mode, the PC· 1500 wi ll
disp l ay the line- number of ea ch pr ogram line and \\lill halt aft er the ex ecut ion of th at li ne . This
allov1s you to fo ll ow (or trace) the sequence of ins.t ructions as they are actua lly pe · rformcd. When
the program pauses aft er t he execu tion of a line. y ou ma y i ns pect or ~l t er the values of va dable s.
The form of the i nstru cti on for initiating th e- Trace mod e is si mp l y: TRON . T he TRON
in st ruc tion ma y be issued as a command {i n RUN mo d e) or it may be embedded .. as a stat eme nt,
within a program. Used as a comma nd, TRO N info rms SHARP th at t rac ing is re qu ir ed during
t
he ex · ec ut ion of a ll subseq ue nt pro grams. Th e prog r ams to be traced are th en started in a normal
manner, wi th a GO TO or RUN com m and .
If TRO N is us ed as a statement, it will i nit i ate the Trace m ode only when the li ne con taining
it is
exec ute d. If, for some reason, th at li ne is never r eached, t he Trace m od e \vi ii remain i nac tive.
On ce initiate d, the Trace mode of o pe ration rema i ns in effect u nt il canceled by a TROFF
i ns tr uctio n. T he TRO FF instr uct i on may also be issued as eit her a co mmand or a st at eme nt.
The Tra ce mode can also be canc eled by the key sequence :
As an
example of ... 1s ing t he Tr a ce mode, en ter t he fo llo,ning program to co m pu te the lengt h
of
the hypotenuse of a triangle given the leng th of the sides:
Pr ogram Listing:
10
IN PUT A. B
2()
A = A*A: B = B*B
30
H = y(A + B)
40
PR INT "HY P OTE NUSE =
'"
H
In RUN mode, issue the T RON c omman d, foll owed by the RUN co mm and. Noti ce th at th e
INPUT command ope rates in t he usual ma nner by disp lay in g a quest i on mark fo r each i np ut
value required.
As soo n as you have ent ered t wo val ue s, the line n umber of the I NP UT st atement
ap pe ars:
RUN
· 1
1 0
By pressing the CD (Up A rr ow) k ey and ho ld ing it. you may r ev iew the en ti re line :
RUN
;-i
I
1 0 IN PUT A, B
To con tinue t he p :r ogram, press the IT) (OO\vn Arro w) key o nc e. This cau ses thie 1)e>:.t li ne to be
execu t ed and its line nu mber to be dis played. Again, you may revi ew the tine wit h the (U p
Arro\v)
key . You may al so che ck the con tents of any variable by t yping its name and pressing
!1! HJl!Jt) :
96
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