HP 15c Manual

 Section 10: The Index Register and Loop Control 111 
 
False (nnnnn > xxx)  True (nnnnn  xxx) 
 instruction  
 ´sV  
loop t. 1  
 Instruction exit loop 
For e: given nnnnn.xxxyy, decrement nnnnn to nnnnn - yy, compare 
it to xxx, and skip the  next program line if the  new value  satisfies nnnnn ≤ 
xxx. This  allows  you  to  exit  a  loop  at  this  point  when nnnnn becomes  less 
than or equal to xxx. 
For example, loop iterations will alter these control numbers as follows: 
Iterations 
Operation 0...

112 Section 10: The Index Register and Loop Control 
 
Keystrokes Display  
l % 2.6458 Indirectly recalls contents of R.2. 
´ X .2 2.6458 Check: same contents recalled by 
directly addressing R.2. 
Exchanging the X-Register 
Keystrokes Display  
´ X V 12.3456 Exchanges  contents  of  RI and  X-
register. 
l V 2.6458 Present contents of RI. 
´ X% 0.0000 Exchanges contents of  R2 (which is 
zero) with X. 
l % 2.6458  
´ X 2 2.6458 Check: directly address R2. 
Storage Register Arithmetic 
Keystrokes Display...

 Section 10: The Index Register and Loop Control 113 
 
Here  is  a  revision  of  the original  radioisotope  decay  program.  This  
time,  we  will  limit  the  program  to  three  executions  of  the  loop  rather  
than setting  a  specific  limit  value.  This  example  uses e with  a  
loop control number in R2 of  
3.0 0 0 0 1. 
     initial loop counter          decrement value 
      test (goal) value 
Make  the  following  changes  to  the  program  (assuming  it  is  in  memory).  A 
loop...

114 Section 10: The Index Register and Loop Control 
 
Keystrokes Display 
15 “ O 
V ´ A 
-15.0000 Branch line number. 
 2.0000 Running  program  loop  counter  
= 3. 
  84.0896  
  5.0000 Loop counter = 2. 
  64.8420  
  8.0000 Loop counter = 1. 
  50.0000  
  50.0000 Loop counter = 0; program ends. 
Example: Display Format Control 
The  following  program  pauses  and  displays  an  example  of • display 
format for each possible decimal place. It utilizes a loop containing a s 
instruction to...

 Section 10: The Index Register and Loop Control 115 
 
To  display  fixed  point notation  for  all  possible  decimal  places  on  the 
HP-15C: 
Keystrokes Display  
| ¥  Run mode. 
´ B 9.000000000  
 8.00000000  
 7.0000000  
 6.000000  
 5.00000  
 4.0000  
 3.000  
 2.00  
 1.0  
 0. Display at ´©instruction. 
 0. Display when program halts. 
Further Information 
Index Register Contents 
Any  value  stored  in  the  Index  register  can  be  referenced  in  three  different 
ways: 
 Using V like...

116 Section 10: The Index Register and Loop Control 
 
I and e 
For  the  purpose  of  loop  control,  the  integer  portion  (the  counter  value)  of 
the stored control number can be up to five digits long (nnnnn.xxxyy). The 
counter value (nnnnn) is zero if not specified otherwise. 
xxx, in  the  decimal  portion  of  the  control  number,  must  be  specified  as  a 
three-digit  number.  (For  example,  ―5‖  must  be  ―005‖.) xxx is  zero  if  not 
specified  otherwise.  Whenever I or e is...

 Section 10: The Index Register and Loop Control 117 
 
An  exception  is  in  the  case  of f where  the  display  format  number  in  RI 
may range  from -6 to +9. (This is discussed in appendix E  on page  247.) A 
number  less  than  zero  will  not  affect  the  display  format,  but  will  affect 
accuracy with this function.  

 
118  

 
 
 
 
 
Part lll 
HP-15C 
Advanced Functions 

 
120 
Section 11 
Calculating With 
Complex Numbers 
The  HP-15C  enables  you  to  calculate  with  complex  numbers,  that  is, 
numbers of the form 
a + ib, 
where     a is the real part of the complex number, 
b is the imaginary part of the complex number, and 
. 
As  you  will  see,  the  beauty  of  calculating  with  the  HP-15C  in  Complex 
mode  is  that  once  the  complex  numbers  are  keyed  in,  most  operations are 
executed in the same manner as with real numbers. 
The Complex Stack and...