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File name: hp 12c pt_user's guide_English_HDPMF123E27 Page: 125 of 275
Printed Date: 2005/8/1 Dimension: 14.8 cm x 21 cm
Section 9
Branching and Looping
Although the instructions in a program normally are executed in order of their
program line numbers, in some situations it is desirable to have program execution
transfer or “branch” to a program line that is not the next line in program memory.
Branching also makes it possible to automatically execute portions of a program
more than once — a process called “looping.”
Simple Branching
The
i
(go to) instruction is used in a program to transfer execution to any
program line. The program line desired is specified by keying its three-digit line
number into the program line containing the
i
instruction. When the
i
instruction is executed, program execution branches or “goes to” the program line
specified and then continues sequentially as usual.
You have already seen a common use of branching: the
gi
000 instruction
(that is stored in program memory after the program you key in) transfers execution
to program line 000. A
i
instruction can be used to branch not only backward
in program memory — as in the case of
gi
000 and as illustrated above —
but also forward in program memory. Backward branching is typically done to
create loops (as described next); forward branching is typically done in
conjunction with a
go
or
gm
instruction for conditional branching (as
described afterward).