132 Section 9: Branching and Looping
These rules can be summarized as "DO if TRUE".
The program line immediately following that containing the conditional test
instruction can contain any instruction; however, the most commonly used
instruction there is i. If a i instruction follows a conditional test instruction,
program execution branches elsewhere in program memory if the condition is true
and continues with the next line in program memory if the condition is false.
Example: The following program calculates income tax at a rate of 20% on
incomes of $20,000 or less and 25% on incomes of more than $20,000. To
conserve program lines, the program assumes that the test value — 20,000 — has
been stored in register R
If a program requires that certain numbers be in the X- and
Y-registers when instructions such as go are executed, it is extremely
helpful when writing the program to show the quantities in each register after
each instruction is executed, as in the following diagram (which shows an
RPN mode program, although it works in a similar way in ALG mode.).
and the tax rates — 20 and 25 — have been stored in