Intel 9800758-02 Trace Facility

BASIC-80 Error Handling
10 ON ERROR GOTO 100
20 INPUT A
30 PRINT 521 A
40 GOTO 20
100 PRINT "Error";ERR;"at line";ERL
110 IF 11=ERR THEN PRINT "Division by zero"
120 RESUME NEXT
RUN
? 13
4
? 0
Error 11 at line 30
Division by zero
?
Trace Facility
The TRON and TROFF (trace on and trace off) commands are used to examine the
execution
of each line. The line number of each program statement executed is
displayed in brackets. The preceding example would run like this after entering
TRON and then RUN:
[10] [20]? • 5 (CR)
[30] 10.4
[40] [20]? • 7 (CR)
[30] 7.428571
[40] [20]? • 0 (CR)
[30] [100] Error 11 at line 30
[110] Division by zero
[120] [40] [20]? •
The ON ERROR OOTO 0 statement has a special meaning. When entered outside of
error handling routines it disables any prior ON ERROR OOTO so that errors are
handled
normally-error messages are displayed and execution is lialted. When
entered inside
an error handling routine, it allows normal handling of a given error
or errors, as shown in the example below.
10 ON ERROR GOTO 100
20 INPUT A,B
30 PRINT AlB
40 PRINT SQR(8-A}
50 STOP
100 IF ERR<>11 THEN 130
110
8=1
120 RESUME
130 ON ERROR GOTO 0
RUN
? 2,0
2
Illegal function call in 40
Ok
The error routine (lines 100-130) sets B to 1 when the divide-by-zero error occurs,
but allows other errors to interrupt operation in a conventional way.
The non-fatal floating-point overflow and divide-by-zero errors are trapped like
other errors. No messages are displayed in this case, and the results
of the calcula-
tions are undefined.
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