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Branching and Looping
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Branching and Looping
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Earlier in this handbook you learned how you can use
GTO
· and a program line
number of ALPHA label to position the calclator to a particular place
in program memory. In addition, you saw how
GTO
·
· positioned the
calculator ot the end of program memory to prepare the calculator
for a new program. You can also use GTO
(go to label) in your programs followed by an ALPHA or numeric
label to transfer execution to any part of a program you desire.
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A GTO instruction used in this way is known
as an unconditional branch. It always branches execution to
the specified label. (Later, you will see how an condition instruction
can be used in conjunction with a GTO to
create a conditional branch—a branch that depends on the
outcome of a test.)
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Here is what a GTO branch would do if a program
in the HP-41C looked like this:
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Execution
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LBLTTEST
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Execution branches to the next
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GTO 01
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LBL 01 in the program.
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LBL 01
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When the program encounters the
GTO 01 instruction, execution immediately halts
and the calculator searches sequentially downward through the program
for the first occurrence of a LBL 01. If the
calculator does not find a LBL 01 before
reaching the end of the program (an END
instruction), the calculator starts searching from the top of the program
until it finds the LBL 01. If the label does
not exist, the HP-41C will display
NONEXISTENT and the
calculator will be positioned to the same line it was prior to beginning
the search. Press
to clear the error.
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