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Section 12: Subroutines 184
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You can use a specific numeric label (like LBL 10) any
number of times in the programs you write. When you branch to that label, the
calculator finds the first occurrence of that label in the current program beginning
from the present location in the program. Refer to Subroutine Types and Label
Searching, page 178, for more information.
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However, note that you should use caution when using the same ALPHA label more
than one time. Since the HP-41C searches all of program memory from the
bottom up for ALPHA labels, only the last occurrence of that label in program
memory will ever be found.
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After the first execution of a subroutine, the HP-41C ‘‘remembers’’
the location of most numeric labels. Subsequent branches to those labels do not
require the time-consuming search. Refer to
appendix G
for more details about label searching.
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When a program is labeled with an ALPHA label, the HP-41C begins searching through all
ALPHA labels beginning at the bottom of program memory. If the ALPHA label is
not found, the display will show NONEXISTENT.
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Beginning with the introduction of this handbook, you have written and executed several
programs that relate to the heat loss of a cylindrical water heater. These programs
included HEAT, CIRCLE, and AREA. Let’s now bring all of these programs together
and form one master program that uses these programs to find the heat loss of the water
heater. To begin, make sure all of these programs have been cleared from program memory
because you will make minor changes and re-load them. Use CLP
and specify the program name to clear them.
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You will create three new programs: BTU, AREA and TEMP. BTU is the master program
that executes the other programs as subroutines and gives the final answer. AREA
computes the area of a cylinder given its height and radius, and TEMP computes the
temperature difference between the heater surface and the air around the heater. Since
AREA and TEMP are outside the master program, they have ALPHA labels and
are terminated with END instructions.
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Since you will use PROMPT so many times when you input the
following programs, first assign the PROMPT function to the
Σ+ key for use in USER mode. Then, each time you
wish to insert a PROMPT instruction in a program, simply press
Σ+ in USER mode.
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