HP 12c Owners Manual

							  Section 8: Programming Basics  101 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 101 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
If the duration of the pause is not long enough to write down the number displayed, 
you can prolong it by using more than one u 
instruction. Alternatively, you can 
have the program automatically stop as described next. 
Stopping Program Execution 
Stopping Program Execution Automatically.
 Program execution is 
automatically halted when the program executes a t
 instruction. To resume 
executing the program from the program line at which execution was halted, press 
t
. 
Example:
 Replace the program above by one containing t
 instructions 
instead of u
 instructions. 
Keystrokes Display   
fs 
00- Sets calculator to Program mode. 
fCLEARÎ 
00- Clears program memory. 
§ 
01-    20 
t 
02-    31Stops program execution to display 
AMOUNT. 
?+1 
03- 44  40   1 
:0 
04-  45  0 
b 
05-    25 
t 
06-    31Stops program execution to display 
TAX. 
?+2 
07- 44  40   2 
+ 
08-    40 
?+3 
09- 44  40   3 
fs 
6,370.52 Sets calculator to Run mode. 
fCLEAR² 
0.00 Clears registers R1 through R6. 
13\68.5 
68.5 First item. 
t 
890.50 AMOUNT for first item. 
t 
60.11 TAX for first item. 
t 
950.61 TOTAL for first item. 
18\72.9 
72.9 Second item. 
t 
1,312.20 AMOUNT for second item. 
t 
88.57 TAX for second item. 
t 
1,400.77 TOTAL for second item.  
						

							102  Section 8: Programming Basics 
 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 102 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
Keystrokes Display   
24\85 
85. Third item. 
t 
2,040.00 AMOUNT for third item. 
t 
137.70 TAX for third item. 
t 
2,177.70 TOTAL for third item. 
5\345 
345. Fourth item. 
t 
1,725.00 AMOUNT for fourth item. 
t 
116.44 TAX for fourth item. 
t 
1,841.44 TOTAL for fourth item. 
:1 
5,967.70 Sum of AMOUNT column. 
:2 
402.82 Sum of TAX column. 
:3 
6,370.52 Sum of TOTAL column. 
Program execution is also automatically halted when the calculator overflows (refer 
to page 73) or attempts an improper operation that results in an Error
 display. 
Either of these conditions signifies that the program itself probably contains an 
error. 
To determine at which program line execution has halted (in order to locate the 
error), press any key to clear the Error
 display, then press fs
 to set the 
calculator to Program mode and display that program line. 
You may also want to display the current program line (by pressing fs
) if 
your program has halted at one of several t
 instructions in your program and 
you want to determine which one that is. To continue executing the program 
afterward: 
1. Press fs to set the calculator back to Run mode. 
2.  If you want to resume execution from the program line at which execution 
halted rather than from line 00, press gi followed by two digit keys that 
specify the program line desired. 
3. Press t to resume execution. 
Stopping Program Execution Manually.
 Pressing any key while a program 
is running halts program execution. You may want to do this if the calculated 
results displayed by a running program appear to be incorrect (indicating that the 
program itself is incorrect). 
To halt program execution during a pause in a running program (that is, when 
u
 is executed), press any key. 
After stopping program execution manually, you can determine at which program 
line execution has halted and/or resume program execution as described above.  
						

							 
103 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 103 of 209   
Printered Date: 2005/7/29    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 two-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 i
00 instruction (that is 
stored in program memory after the program you key in) transfers execution to 
program line 00. A i
 instruction can be used to branch not only backward in 
program memory — as in the case of i
00 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 
an o
 or m
 instruction for conditional branching (as described afterward).  
						

							104  Section 9: Branching and Looping 
 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 104 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
Looping 
If a i
 instruction specifies a lower-numbered line in program memory, the 
instructions in the program lines between the specified line and the i
 instruction 
will be executed repeatedly. As can be seen in the illustration above under Simple 
Branching, once the program begins executing the “loop” it will execute it again 
and again. 
If you want to terminate the execution of a loop, you can include an o
 or m
 
instruction (described below) or an t
 instruction within the loop. You can also 
terminate execution by pressing any key while the loop is being executed. 
Example:
 The following program automatically amortizes the payments on a 
home mortgage without requiring you to press f!
 for each payment. It will 
amortize one month’s payments each time or one year’s payments each time the 
loop is executed, depending on whether the number 1 or 12 is in the display 
when you start running the program. Before running the program, we’ll “initialize” 
it by storing the required data in the financial registers — just as we would do if 
we were amortizing a single payment manually. We’ll run the program for a 
$50,000 mortgage at 12
3/4% for 30 years, and we’ll key 1 into the display just 
before running it in order to amortize monthly payments. For the first two “passes” 
through the loop we’ll execute the program one line at a time, using Ç
, so that 
we can see the looping occurring; then we’ll use t
 to execute the entire loop a 
third time before terminating execution. 
Keystrokes Display   
fs 
00- Sets calculator to Program mode. 
fCLEARÎ 
00- Clears program memory 
?0 
01-  44  0Stores the number from the display 
into register R
0. This number will be 
the number of payments to be 
amortized.  
						

							  Section 9: Branching and Looping  105 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 105 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
Keystrokes Display   
:0 
02-  45  0Recalls the number of payments to 
be amortized. This program line is 
the one to which pro
gram execution 
will later branch. It is included 
because after the first time the loop 
is executed, the number in the 
“display”
*  is replaced by the result 
of !
. 
f! 
03-  42  11Amortizes payment(s). 
gu 
04-  43  31Pauses to display amount of 
payment(s) applied to interest. 
~ 
05-    34Brings amount of payment(s) 
applied to principal into “display.”* 
gu 
06-  43  31Pauses to display amount of 
payment(s) applied to principal. 
gi02 
07- 43, 33   02Transfers program execution to line 
02, so that the number of payments 
to be amortized can be recalled to 
the display before the !
 
instruction in line 03 is executed. 
fs 
0.00 Sets calculator to Run mode. 
(Display shown assumes no results 
remain from previous calculations.) 
fCLEARG 
0.00 Clears financial registers. 
30gA 
360.00 Enters n. 
12.75gC 
1.06 Enters i. 
50000$ 
50,000.00 Enters PV. 
g 
50,000.00 Sets payment to End. 
P 
–543.35 Calculates the monthly payment. 
0n 
0.00 Reset n to zero. 
1 
1. Keys 1 into the display to amortize 
monthly payments. 
Ê 
01-  44  0Line 01: ?
0. 
 
1.00  
                                                 
*  More precisely, the number in the X-register.  
						

							106  Section 9: Branching and Looping 
 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 106 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
Keystrokes Display   
Ê 
02-  45  0Line 02: :
0. This is the beginning 
of the first pass through the loop. 
 
1.00  
Ê 
03-  42  11Line 03: f!
. 
 
–531.25 Portion of first month’s payment 
applied to interest. 
Ê 
04-  43  31Line 04: gu
. 
 
–531.25  
Ê 
05-    34Line 05: ~
. 
 
–12.10 Portion of first month’s payment 
applied to principal. 
Ê 
06-  43  31Line 06: gu
. 
 
–12.10  
Ê 
07- 43, 33   02Line 07: gi
02. This is the end 
of the first pass through the loop. 
 
–12.10  
Ê 
02-  45  0Line 02: :
0. Program execution 
has branched to the beginning of 
the loop for the second pass throu
gh 
it. 
 
1.00  
Ê 
03-  42  11Line 03: f!
. 
 
–531.12 Portion of second month’s payment 
applied to interest. 
Ê 
04-  43  31Line 04: gu
. 
 
–531.12  
Ê 
05-    34Line 05: ~
. 
 
–12.23 Portion of second month’s payment 
applied to principal. 
Ê 
06-  43  31Line 06: gu
. 
 
–12.23   
						

							  Section 9: Branching and Looping  107 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 107 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
Keystrokes Display   
Ê 
07- 43, 33   02Line 07: gi
02. 
This is the end of the second pass 
through the loop. 
 
–12.23  
t 
–530.99 Portion of third month’s payment 
applied to interest. 
 
–12.36 Portion of third month’s payment 
applied to principal. 
t(or any key) 
–12.36 Halts program execution. 
Conditional Branching 
Often there are situations when it is desirable for a program to be able to branch 
to different lines in program memory, depending on certain conditions. For 
example, a program used by an accountant to calculate taxes might need to 
branch to different program lines depending on the tax rate for the particular 
income level. 
The hp 12c provides two conditional test instructions that are used in programs for 
conditional branching: 
z  o tests whether the number in the X-register (represented by the x in the 
key symbol) is less than or equal to the number in the Y-register (represented 
by the y in the key symbol). As discussed in Appendix A, the number in the 
X-register is simply the number that would, if the calculator were in Run mode, 
be currently in the display; and the number in the Y-register is the number 
that would, if the calculator were in Run mode, have been in the display 
when \ was pressed. For example, pressing 4\5 would place the 
number 4 in the Y-register and the number 5 in the X-register. 
z  m tests whether the number in the X-register is equal to zero. 
The possible results of executing either of these instructions are: 
z  If the condition tested for is true when the instruction is executed, program 
execution continues sequentially with the instruction in the next line of 
program memory. 
z  If the condition tested for is false when the instruction is executed, program 
execution skips the instruction in the next line of program memory and 
continues with the instruction in the following line. 
These rules can be summarized as “DO if TRUE”.  
						

							108  Section 9: Branching and Looping 
 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 108 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
 
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
0 and the tax rates — 20 and 25 — have been stored in 
registers R
1 and R2, respectively. 
Note: If a program requires that certain numbers be in the X- and 
Y-registers when instructions such as o 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.  
						

							  Section 9: Branching and Looping  109 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 109 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
 
We’ll key the income into the display before running the program so that it will be 
in the X-register when the :
0 instruction in program line 01 is executed. This 
instruction will place the test value 20,000 in the X-register and (as explained in 
Appendix A) move the income into the Y-register. The ~
 instruction in program 
line 02 will exchange the numbers in the X- and Y-registers (as also explained in 
Appendix A): that is, it will place the income back into the X-register and place the 
test value into the Y-register. This is necessary because when either the :
2 
instruction in line 05 or the :
1 instruction in line 07 is executed, the number in 
the X-register is moved into the Y-register; if the ~ 
instruction were not included, 
the test value 20,000, rather than the income, would be in the Y-register when the 
b
 instruction in line 08 is executed. 
Keystrokes Display   
fs 
07- 43, 33   02Sets calculator to Program mode. 
(Display shows program line at 
which execution was halted at end 
of preceding example.) 
fCLEARÎ 
00- Clears program memory. 
:0 
01-  45  0Recalls test value into X-register and 
places income in Y-register. 
~ 
02-    34Places income in X-register and test 
value in Y-register. 
go 
03-  43  34Tests whether number in X-register 
(income) is less than or equal to 
number in Y-register (20,000).  
						

							110  Section 9: Branching and Looping 
 
 
File name: hp 12c_users guide_English_HDPMBF12E44  Page: 110 of 209   
Printered Date: 2005/7/29    Dimension: 14.8 cm x 21 cm 
 
Keystrokes Display   
gi07 
04- 43, 33   07If condition is true, branches to 
program line 07. 
:2 
05-  45  2If condition is false, recalls 25% tax 
rate to X-register. 
gi08 
06- 43, 33   08Branches to program line 08. 
:1 
07-  45  1Recalls 20% tax rate to X-register. 
b 
08-    25Calculates tax. 
fs 
–12.36 Sets calculator to Run mode. 
(Display shows results of running of 
previous program.) 
Now, well store the required numbers in registers R
0, R1, and R2, then we’ll run the 
program, using Ç
 so that we can check that the branching occurs properly. It’s 
good practice with programs containing conditional test instructions to check that 
the program branches correctly for all possible conditions: in this case, if the 
income is less than, equal to, or greater than the test value. 
Keystrokes Display   
20000?0 
20,000.00 Stores test value in register R0. 
20?1 
20.00 Stores 20% tax rate in register R1. 
25?2 
25.00 Stores 25% tax rate in register R2. 
15000 
15,000. Keys income less than test value into 
display and X-register. 
Ê 
01-  45  0Line 01: :
0. 
 
20,000.00 Test value has been recalled to 
X-register, moving income to 
Y-register. 
Ê 
02-    34Line 02: ~
 
 
15,000.00 Income has been placed in 
X-register and test value has been 
placed in Y-register. 
Ê 
03-  43  34Line 03: go
 
 
15,000.00  
Ê 
04- 43, 33   07Condition tested by o
 was true, 
so program execution continued 
with line 04: gi
07.