Error Correction In The Program Mode - Sharp PC-1500A Instruction Manual

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Notice how each line in the program accomplishes a single complete and necessary step. Line
10 erases any previous values which might be contained in the variables NI, N2, and NJ {this is a
precaution in case t he user fails to enter all three numbers). Line 20 collects the data lrom the
user. Line
30
averages the numbers.
Line 40 computes the three
differences. Li ne
50
sums the
dillerences and line 60 prints the result.
It is no accident that the instructions on each line correspond to the English language descrip-
tion of the program. Instead , this is one of the principles of good programming which you should
try to follow.
Unlike the use o·f abbreviations. the use o f the colon docs affect the amount o f memory used
to store the program. This is the chief justification fo r using the colon to place several statements
on one line. Each ' l ine number reserves several program "steps" (a unit of storage) and therefore
the fewer the line numbers in a program, the smaller memory size of the program.
The f inal statement about the use of the colon is that each programmer must balance each
program's readab ility and changeability against the storage needs of his application.
J. Error Correction in the Program Mode
Although abbreviations and colons help us to easily enter programs, they cannot prevent the
best of us from making mistakes. Even profcss:ional programmers fail to catch errors when
reviewing their own programs. What this means is that sooner or later you will encounter an error
while running your program {if you haven't already). Most of these errors are easily corrected if
you simply accept t hem as a puzzle to be solved a nd carefully track down the problem. Several
features of the PC· 1 SOOA will assist you in this.
Upon d iscoverin.g an incorrect statement SHARP will halt and indicate the problem with a
terse message such as:
[i ~ RQR~l~_ l _ N ~ 2_0 ~-R - uN ~ ~~
Let's create
a
program with a del iberate error for purposes of illustration. Enter :
Program Listing:
25
PAUSE "HUMPTY OUMPTY"
50
PR IMT "WAS AN EGGHEAD"
Keystrokes:
r n m m rn rnOOCTJl sHon l l:::::J00W 00 ffiffiffi lsPAC£1
rn
w
oo mm m
1SH• " 1
c:::J
1 • ., •• 1
oo rn mm co oo m
1 """'1
c::i
oo rn oo , ...
'"'1
mm
ISP•c•I CT] [li] CT[)
QO(D[D
rnJ
IStt1rr l
l:::::J
l••TE• I
Now run the program. When the error message appears depress the
OJ
{Up Arrow} key.
As long as you hold this key, the display will show the line on which SHARP became confused.
The flash ing grid may provide a hint as to the nature of the problem.
To correct the bad statement, press
!ID
to quit the program and switch to the PROgram
mode. Press the Up Arrow key, but do not hold it, and the display will again show the erroneous
line:
42
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