RPN: HP 15C and DM32: Integer Length and Digit Extraction

RPN: HP 15C and DM32: Integer Length and Digit Extraction (up to 99,999,999)

The following programs are utilities for positive integers:

(1) Integer Length: how many digits in a positive integer

(2) Digit Extraction: Get the nth digit of a positive integer

Note:  Do not use more than 8 digits (integers up to 99,999,999).   Beyond this, the program may return inaccurate answers.  

Thanks to J-F Garnier for pointing out the limitation of the programs.  

Integer Length

Find the number of digits of a positive integer. The integer is decimal base (base 10).

For a positive integer n, the number of the digits can be easily found by the formula:

L = int(log(x)) + 1

DM32, HP 32S, HP 32SII Code

L01 LBL L

L02 LOG

L03 IP

L04 1

L05 +

L06 RTN

HP 15C, DM15 Code

001	42, 21, 11	LBL A
002	43, 13	LOG
003	43, 44	INT
004	1	1
005	40	+
006	43, 32	RTN

The program finds the number of digits in the positive integer in the X stack.

Examples:

X = 436782; Length: 6

X = 5195008; Length: 7

X = 23156956; Length: 8

Digit Extraction

Extract the nth digit of a positive integer. Digit positions go from left to right. For example: for the integer 4582, the 1^st digit is 4, the 2^nd digit is 5, 3^rd digit is 8, and 4^th digit is 2.

Steps that this program follows:

Step 1: Find the length of the positive integer. L = int(log(x)) + 1.

Step 2: Divide X by 10^(L – n + 1). D = X / (10^(L – n + 1))

Step 3: Extract the fractional part. D = frac(D)

Step 4: Multiple the result by 10 and extract the integer part. D = int(10 * D)

Setting up the stack:

Y: integer

X: nth digit to extract

Variables Used:

DM32, HP 32S, HP 32S II	HP 15C, DM15
X	R1
N	R2
L	R3

DM32, HP 32S, HP 32SII Code

E01 LBL E

E02 STO N

E03 R↓

E04 STO X

E05 LOG

E06 IP

E07 1

E08 +

E09 STO L

E10 RCL X

E11 RCL L

E12 RCL- N

E13 1

E14 +

E15 10^x

E16 ÷

E17 FP

E18 10

E19 ×

E20 IP

E21 RTN

HP 15C, DM15 Code

001	42, 21, 12	LBL B
002	44, 2	STO 2
003	33	R↓
004	44, 1	STO 1
005	43, 13	LOG
006	43, 44	INT
007	1	1
008	40	+
009	44, 3	STO 3
010	45, 1	RCL 1
011	45, 3	RCL 3
012	45, 30, 2	RCL- 2
013	1	1
014	40	+
015	13	10^x
016	10	÷
017	42, 44	FRAC
018	1	1
019	0	0
020	20	×
021	43, 44	INT
022	43, 32	RTN

Examples

Integers	Length	2nd Digit	4th Digit	5th Digit
436782	6	3	7	8
5195008	7	1	5	0
23156956	8	3	5	6

Eddie

All original content copyright, © 2011-2025. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.

All posts are 100% generated by human effort.  The author does not use AI engines and never will.

RPN with HP 15C and DM32: Complex Mode

RPN with HP 15C and DM32: Complex Mode

HP 15C Complex Mode

This section also applies to the Swiss Micros DM15 family.

Complex mode is a separate mode for the HP 15C. Complex mode is turned on by setting flag 8. Complex mode is on when there is a “C” indicator in the display.

In complex mode, the stack is expanded. Each stack level now includes a real part and a complex part. What is in the display is always the real part.

Stack T	Real part of T	Imaginary part of T
Stack Z	Real part of Z	Imaginary part of Z
Stack Y	Real part of Y	Imaginary part of Y
Stack X	Real part of X	Imaginary part of X

The great news is that the stack handles up to four complex numbers, one for each of the stack levels.

To display the imaginary part, we have two methods:

Temporary View: Press [ f ] and hold [ COS ] (i) to temporarily view the complex part. The stack remains unaffected.

Switch: Switch the real part and the imaginary part by pressing [ f ] [ - ] (Re<>Im). Doing this switches the real and imaginary parts of the X stack.

For example: X = 9 – 8i

Enter the complex number as such: 9 [ ENTER ] 8 [ CHS ] [ I ] * (see note).

The displays shows 9.

Press [ f ] [ - ] (Re<>Im). The display shows -8 and the X stack now has the complex number X = -8 + 9i.

Press [ f ] [ - ] (Re<>Im) to switch the parts back to the original complex number.

* Note: If complex mode is turned off (no C indicator), using this key sequence sets flag 8, turning on complex mode automatically.

The switching of parts is important, because memory registers can not hold an entire complex number, but it’s separate parts. Thus, we will need two registers, one for the real part and one for the imaginary part.

HP 15C: Leaving Complex Mode

To leave complex mode, clear flag 8 (CF 8). The imaginary parts of the stack are lost.

Angle Mode

In complex mode, the trigonometric functions operate as the angles are always in radian measure regardless of the angle setting. The only functions that recognize the angle setting are the polar/rectangular conversions. To take the cosine and sine of angle that respects the conversion, use the following sequence:

angle [ENTER] 1 [ f ] [ →R ]: X stack: cos(angle), Y stack: sin(angle)

HP 15C - Solving Monic Quadratic Equations

The HP 15C’s solver only works for real numbers, so manual methods and formulas must be used to solve equations for complex numbers.

Z^2 + w1 * Z + w0 = 0

Solution: Z = (w1 ± √(w1^2 – 4 * w0)) / 2

(D = √(w1^2 – 4 * w0), Z+ = (w1 + D) / 2 Z- = Z+ - D)

Store the following:

Complex coefficient w1: Real part in register 4, Imaginary part in register 5

Complex coefficient w2: Real part in register 1, Imaginary part in register 2

The results are stored in the following registers:

Discriminant (D): Real part in register 6, imaginary part in register 3

Complex root Z+: Real part in register .0 (decimal point-0), imaginary party in register 8

Complex root Z-: Real part in register 9, imaginary part in register 7

Code (use any label you want, I use label A for example):

Key	Key Code		Key	Key Code
LBL A	42, 21, 11		RCL 4	45, 4
SF 8	43, 4, 8		RCL 1	45, 1
RCL 4	45, 4		I	42, 25
RCL 1	45, 1		-	30
I	42, 25		2	2
x^2	43, 11		÷	10
RCL 5	45, 5		STO .0	44, .0
RCL 2	45, 2		Re<>Im	42, 30
I	42, 25		STO 8	44, 8
4	4		Re<>Im	42, 30
×	20		R/S	31
-	30		RCL 6	45, 6
√	11		RCL 3	45, 3
STO 6	44, 6		I	42, 25
Re<>Im	42, 30		-	30
STO 3	44, 3		STO 9	44, 9
Re<>Im	42, 30		Re<>Im	42, 30
			STO 7	44, 7
			Re<>Im	42, 30
			RTN	43, 32

Example:

Z^2 + (4 + i) * Z + (2 - 5i) = 0

w1: 4 STO 4, 1 STO 1

w2: 2 STO 5, 5 CHS STO 2

[ f ] A or [ GSB ] A:

0.11724 [ f ] hold (i) 1.15309 (Z+ ≈ 0.11724 + 1.15309i)

[ R/S ]

-4.11724 [ f ] hold (i) -2.15309 (Z- ≈ -4.11724 – 2.15309i)

DM32 Complex Mode

This section also applies to the HP 32Sii, HP 32S, and the HP 41C/DM41X with the Advantage ROM plugged in. The names of the functions vary.

There is no “separate” complex mode for the DM32, all the functions are access with shifted CMPLX prefix function. The complex number functions available on the DM32 are:

CMPLX+, CMPLX-, CMPLX×, CMPLX÷

CMPLX+/- (change sign, multiply the complex number by -1)

CMPLX1/x, CMPLXe^x, CMPLXLN, CMPLXy^x

CMPLXSIN, CMPLXCOS, CMPLXTAN

The complex functions grabs the values from the four stack levels and uses them as up to two complex numbers:

Z	Imaginary part of T + Zi
T	Real part of T + Zi
Y	Imaginary part of X + Yi
X	Real part of X + Yi

Memory registers can not hold an entire complex number, but it’s separate parts. Thus, we will need two registers, one for the real part and one for the imaginary part.

To enter complex numbers, enter the imaginary part, press [ ENTER ], then enter the real part.

Square Root and Square (√ and x^2)

There is no complex square root or complex square function. We will need some creativity to tackle these functions. Here is just one way we can accomplish this task.

Assume the complex number A + Bi have the real part stored in A and imaginary part stored in B.

Square Root (√):

RCL B

RCL A

0.5

ENTER

Clx

x<>y

CMPLXy^x

Square (x^2):

RCL B

RCL A

RCL B

RCL A

CMPLX×

Angle Mode

In complex mode, the trigonometric functions operate as the angles are always in radian measure regardless of the angle setting. The only functions that recognize the angle setting are the polar/rectangular conversions. To take the cosine and sine of angle that respects the conversion, use the following sequence:

1 [ENTER] angle [ blue shift ] [ →y,x ]: X stack: cos(angle), Y stack: sin(angle)

(HP 32SII late editions: lavender/purple shift)

DM32 - Solving Monic Quadratic Equations

Like the HP 15C, the DM32’s solver only works for real numbers, so manual methods and formulas must be used to solve equations for complex numbers.

Z^2 + w1 * Z + w0 = 0

Solution: Z = (w1 ± √(w1^2 – 4 * w0)) / 2

(D = √(w1^2 – 4 * w0), Z+ = (w1 + D) / 2 Z- = Z+ - D)

Store the following:

Complex coefficient w1: Real part in A, Imaginary part in B

Complex coefficient w2: Real part in C, Imaginary part in D

The program will prompt for A, B, C, and D, in the order of imaginary part, then real part

Z^2 + (Bi + A) * Z + (Di + C) = 0

The results are stored in the following registers:

Discriminant (D): Real part in E, imaginary part in F

Complex root Z+: Real part in R, imaginary party in S

Complex root Z-: Real part in U, imaginary part in V

Code:

A01 LBL A	A24 x<>y
A02 INPUT B	A25 RCL B
A03 INPUT A	A26 RCL A
A04 INPUT D	A27 CMPLX-
A05 INPUT C	A28 2
A06 RCL B	A29 ENTER
A07 RCL A	A30 CLx
A08 RCL B	A31 x<>y
A09 RCL A	A32 CMPLX÷
A10 CMPLX×	A33 STO S
A11 4	A34 x<>y
A12 RCL× D	A35 STO R
A13 4	A36 x<>y
A14 RCL× C	A37 STOP
A15 CMPLX-	A38 RCL F
A16 0.5	A39 RCL E
A17 ENTER	A40 CMPLX-
A18 CLx	A41 STO U
A19 x<>y	A42 x<>y
A20 CMPLXy^x	A43 STO V
A21 STO E	A44 x<>y
A22 x<>y	A45 RTN
A23 STO F

Example:

Z^2 + (4 + i) * Z + (2 - 5i) = 0

[ XEQ ] A

B? 1 [R/S]

A? 4 [R/S]

D? -5 (5 [+/-] ) [R/S]

C? 2 [R/S]

Y: 1.15309, X: 0.11724 (Z+ ≈ 0.11724 + 1.15309i)

[R/S]

Y: -2.15309, X: -4.11724 (Z- ≈ -4.11724 – 2.15309i)

I hope you enjoyed this edition of RPN with HP 15C and DM2,

Eddie

All original content copyright, © 2011-2025. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.