Flags
A flag is an indicator of status. It is either set (true) or clear (false). Testing a flag is
another conditional test that follows the "Do if true" rule: program execution
proceeds directly if the tested flag is set, and skips one line if the flag is clear.
Meanings of Flags
The HP 35s has 12 flags, numbered 0 through 11. All flags can be set, cleared,
and tested from the keyboard or by a program instruction. The default state of all 12
flags is clear. The three–key memory clearing operation described in appendix B
clears all flags. Flags are not affected by
Flags 0, 1, 2, 3, and 4 have no pre-assigned meanings. That is, their states
will mean whatever you define them to mean in a given program. (See the
example below.)
Flag 5, when set, will interrupt a program when an overflow occurs within the
program, displaying and
exceeds the largest number that the calculator can handle. The largest
possible number is substituted for the overflow result. If flag 5 is clear, a
program with an overflow is not interrupted, though is displayed
briefly when the program eventually stops.
Flag 6 is automatically set by the calculator any time an overflow
occurs (although you can also set flag 6 yourself). It has no effect, but can be
tested. Besides, when using non-decimal bases in programs, flag 6 also gets
set for in programs.
Flags 5 and 6 allow you to control overflow conditions that occur during a
program. Setting flag 5 stops a program at the line just after the line that
caused the overflow. By testing flag 6 in a program, you can alter the
program's flow or change a result anytime an overflow occurs.
Flags 7, 8 and 9 control the display of fractions. Flag 7 can also be controlled
from the keyboard. When Fraction–display mode is toggled on or off by
pressing
, flag 7 is set or cleared as well.
()
. An overflow occurs when a result
Programming Techniques
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.
14-9