The Museum of HP Calculators

Mastermind for the HP-41C

This program is by Wouter Peters and is used here by permission.

This program is supplied without representation or warranty of any kind. Wouter Peters and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

Overview

Mastermind is originally a kind of board game for two. The board of the game consist of a series of four-holed rows. One is covered to hide it from one player. The other rows have four small 'marker' holes at one side.

The first player puts together a row of four coloured pegs. There are usually six colours available. Two or more pegs of the same colour are allowed. This array is hidden from the other player.

The other player has to discover the colours and positions of the pegs by putting together reasoned guesses of usually four coloured pegs (less than four pegs in one guess is allowed though, only the placed pegs will be evaluated). A guess is evaluated by the first player and is rewarded a white marker for every peg of the right colour that is placed in a wrong position and a black marker for every peg of the right colour thatís in the right place. These marker pegs are plugged into the marker-holes. The aim is to find the right configuration in as few as possible guesses.

Mastermind - HP 41 C as the composer/evaluator

The composition of a hidden row and evaluation of the guesses can be programmed into a HP 41C. The display can't show colours so we'll use figures instead. I've chosen to enter a guess as a four-digit number. This limits the number of 'colours' to 9. The figure '0' is reserved for an empty hole in a row (incomplete guess). The number of colours isn't hard coded though and all numbers of colours between 1-9 can be chosen (see Register use below). This is sufficient, as the classic Mastermind is played with pegs of six colours.

The HP can only show one row of pegs with markers so either we must use the printer or use pen and paper to represent the board to keep track of the earlier guesses. This program can be run on a HP 41 C with or without a printer connected.

The calculator will generate a hidden array of four figures randomly chosen within the range of possible 'colours' and then prompt the player for his or her first guess. A guess is entered as a four-digit number. It is then parsed and processed. The program will return the appropriate white (0) or black (*) markers or will beep and return 'RIGHT' on a right guess.

A few notes on the program listing:

  1. I haven't found a suitable character on my PC for the 'lazy T' associated with APPEND. The few times it occurs in the listing below (in lines 101, 111, 119 and 132) Iíve typed it as Ďltí. So these are APPEND <space>, APPEND '*', APPEND '0' and APPEND 'RIGHT'
  2. A few Extended Functions are used: RCLFLAG, STOFLAG and REGMOVE. The first two are not really necessary. They have only a cosmetic function: to restore the numerical display format back to the state from before Mastermind was run (Mastermind needs a FIX 0 display). REGMOVE offers an easy way to copy registers 1-4 into 11-14 (Line 044, 045), but it can easily be rewritten to a series of RCL and STO statements to get the same result: a copy of Reg 1-4 into Reg 11-14.

Size= 21

Use of registers:
R00= Random seed
R01= code A
R02= code B
R03= code C
R04= code D
R05= guess A
R06= guess B
R07= guess C
R08= guess D
R09= # of right guessed places
R10= loop counter #1
R11= scratch A
R12= scratch B
R13= scratch C
R14= scratch D
R15= address pointer #1
R16= address pointer #2
R17= # of right guessed figures
R18= loop counter #2
R19= # of possible figures
R20= num.display format flags

How to play the game

  1. Decide on the number of different figures you want to use and store this into register 19. To play in the classic setup: 6 STO 19
  2. XEQ "MM" will generate an hidden array and prompts you for the first guess ("?" in the display)
  3. enter for instance 1234 and press R/S . After your guess is parsed you'll see "1,2,3,4," scrolling through the display instead of the flying goose (a trick using a bug, the ignore error flag (25) and a flag operation on a nonexisting flag (any > 55), after evaluation of your guess it's marked, your marked guess displayed (for instance "1,2,3,4, *OO" one in a right place, two right figures in wrong places), a TONE is executed (no printer) or the output printed and the program STOPs. Now you can study your guess(es) deduct a new one enter it and press R/S again.
  4. Repeat 3 until you've got it right. The calculator will BEEP and you get a display saying that you had it right (for instance: '6,4,3,2 RIGHT'). The program winds up (restores the original numerical display format) and halts at the END, so you can simply start another play by pressing R/S.

Program

001 LBL "MM"
002 RCLFLAG
003 STO 20
004 FIX 0
005 4	
006 STO 10
007 LBL 01
008 XEQ 11
009 RCL 19
010 *
011 INT
012 1
013 +
014 STO IND 10
015 DSE 10
016 GTO 01
017 CF 22
018 LBL A
019 FC? 22
020 ?
021 FC? 22
022 PROMPT
023 1 E4
024 /
025 STO L
026 XEQ 12
027 STO 05
028 XEQ 12
029 STO 06
030 XEQ 12
031 STO 07
032 XEQ 12
033 STO 08
034 CLA
035 ARCL 05
036 ARCL 06
037 ARCL 07
038 ARCL 08
039 FS? 55
040 CF 21
041 SF 25
042 AVIEW
043 SF 99
044 1,011004
045 REGMOVE
046 5
047 STO 15
048 11
049 STO 16
050 4
051 STO 10
052 STO 18
053 STO 17
054 STO -17
055 LBL 02
056 RCL IND 15
057 RCL IND 16
058 X=Y?
059 GTO 03
060 1
061 ST+ 16
062 DSE 10
063 GTO 02
064 GTO 04
065 LBL 03
066 ISG 17
067 STO X
068 PI
069 STO IND 16
070 LBL 04
071 1
072 ST+15
073 11
074 ST 16
075 4
076 STO 10
077 DSE 18
078 GTO 02
079 STO 09
080 ST- 09
081 RCL 01
082 RCL 05
083 X=Y?
084 ISG 09
085 STO X
086 RCL 02
087 RCL 06
088 X=Y?
089 ISG 09
090 STO X
091 RCL 03
092 RCL 07
093 X=Y?
094 ISG 09
095 STO X
096 RCL 04
097 RCL 08
098 X=Y?
100 STO X
101 "lt "
102 RCL 09
103 ST- 17
104 STO 10
105 X=0?
106 GTO 06
107 4
108 X=Y?
109 GTO 09
110 LBL 05
111 "lt*"
112 DSE 10
113 GTO 05
114 LBL 06
115 RCL 17
116 X=0?
117 GTO 08
118 LBL 07
119 "ltO"
120 DSE 17
121 GTO 07
122 LBL 08
123 FS? 55
124 SF 21
125 AVIEW
126 FC? 55
127 TONE 7
128 CF 22
129 STOP
130 GTO A
131 LBL 09
132 "ltRIGHT"
133 FS? 55
134 SF 21
135 AVIEW
136 BEEP
137 ADV
138 GTO 10
139 LBL 11
140 RCL 00
141 9821
142 *
143 .211327
144 +
145 FRC
146 STO 00
147 RTN
148 LBL 12
149 LASTX
150 FRC
151 10
152 *
153 INT
154 RTN
155 LBL 10
156 RCL 20
157 36,41
158 STOFLAG
159 END

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