Using Flags - HP -11C Owner's Handbook Manual

116 Section 7: Program Decisions and Control
Using Flags
Like the x: y and x:0 conditional tests, flags give you the capability
to either skip or execute individual lines in program memory.
However, while the x:y and x:0 conditionals function by
comparing values, flags function by telling the calculator status.
That is, if a set flag ((9](SF]n) instruction is placed in a program
branch, testing that flag elsewhere ((¢] n) can tell the
calculator whether or not that branch has been executed.
Example. The following program closely approximates the
conversion of an input in miles to kilometers ((f] [A]), or the
conversion of an input in kilometers to miles ({f)[B)). The calculator
uses the status of flag 0 to decide whether to convert a user input to
kilometers (multiply input by conversion factor) or to miles (divide
input by conversion factor).
Key in
kilometers.
Start
Set flag.
Place
1.6093
in X-register.
~~ ~~
eee ee
ee ee
Section 7: Program Decisions and Control 117
Keystrokes Display
((F7R 000- Sets HP-11C to Program
mode.
(ACLEAR [PRGM 000- Clears program memory.
LBLI[A 001-42,21,11 Program begins with
input in miles.
(s){cFEJo 002-43, 5, 0 Flag Ocleared
("remembers" miles input
for later program control).
Gro}! 003- 22 1 Unconditional branch to
LBL)1.
(eC) (B) 004-42,21,12 Program begins with
input in kilometers.
9 )(SFJO 005-43, 4, 0 Flag 0 set (''remembers"
kilometers input for later
in program).
(cet) 1 006-42,21, 1 ((BL)1 begins
calculation portion of
program.
1 007- 1
QO 008- 48
6 o0g- 6 \ Place conversion factor
0 010- O (in X-register.
9 011- 9
3 012- 3
9)(F)0 013-43, 6, O Flag test. If true (kilo-
GTO|2 014- 22 2 = meters input), go to(LBL)2.
x 015- 20 = If flag test false (miles in-
9 )(RTN 016- 4332 put), calculate conversion
to kilometers and halt
program.
(LBL) 2 017-42,21, 2 Calculate conversion to
& 018- 10 miles and halt program.
Ca) (RIN 019- 4332
9 |[P/R Sets HP-11C to Run mode,
Run the program to convert 26 miles into kilometers; to convert 1.5
kilometers into miles.