games/arithmetic/arithmetic.c

   1 /*-
   2  * Copyright (c) 1989, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Eamonn McManus of Trinity College Dublin.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  33  * @(#)arithmetic.c     8.1 (Berkeley) 5/31/93
  34  * $FreeBSD: src/games/arithmetic/arithmetic.c,v 1.10 1999/12/12 06:40:28 billf Exp $
  35  * $DragonFly: src/games/arithmetic/arithmetic.c,v 1.4 2005/04/24 15:31:30 liamfoy Exp $
  36  */
  37
  38 /*
  39  * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
  40  *
  41  * The operation of this program mimics that of the standard Unix game
  42  * `arithmetic'.  I've made it as close as I could manage without examining
  43  * the source code.  The principal differences are:
  44  *
  45  * The method of biasing towards numbers that had wrong answers in the past
  46  * is different; original `arithmetic' seems to retain the bias forever,
  47  * whereas this program lets the bias gradually decay as it is used.
  48  *
  49  * Original `arithmetic' delays for some period (3 seconds?) after printing
  50  * the score.  I saw no reason for this delay, so I scrapped it.
  51  *
  52  * There is no longer a limitation on the maximum range that can be supplied
  53  * to the program.  The original program required it to be less than 100.
  54  * Anomalous results may occur with this program if ranges big enough to
  55  * allow overflow are given.
  56  *
  57  * I have obviously not attempted to duplicate bugs in the original.  It
  58  * would go into an infinite loop if invoked as `arithmetic / 0'.  It also
  59  * did not recognise an EOF in its input, and would continue trying to read
  60  * after it.  It did not check that the input was a valid number, treating any
  61  * garbage as 0.  Finally, it did not flush stdout after printing its prompt,
  62  * so in the unlikely event that stdout was not a terminal, it would not work
  63  * properly.
  64  */
  65
  66 #include <sys/types.h>
  67 #include <ctype.h>
  68 #include <signal.h>
  69 #include <stdio.h>
  70 #include <stdlib.h>
  71 #include <string.h>
  72 #include <time.h>
  73 #include <unistd.h>
  74
  75 int getrandom(int, int, int);
  76 void intr(int);
  77 int opnum(int);
  78 void penalise(int, int, int);
  79 int problem(void);
  80 void showstats(void);
  81 static void usage(void);
  82
  83 const char keylist[] = "+-x/";
  84 const char defaultkeys[] = "+-";
  85 const char *keys = defaultkeys;
  86 int nkeys = sizeof(defaultkeys) - 1;
  87 int rangemax = 10;
  88 int nright, nwrong;
  89 time_t qtime;
  90 #define NQUESTS 20
  91
  92 /*
  93  * Select keys from +-x/ to be asked addition, subtraction, multiplication,
  94  * and division problems.  More than one key may be given.  The default is
  95  * +-.  Specify a range to confine the operands to 0 - range.  Default upper
  96  * bound is 10.  After every NQUESTS questions, statistics on the performance
  97  * so far are printed.
  98  */
  99 int
 100 main(int argc, char *argv[])
 101 {
 102         int ch, cnt;
 103
 104         /* Revoke setgid privileges */
 105         setgid(getgid());
 106
 107         while ((ch = getopt(argc, argv, "r:o:")) != -1)
 108                 switch(ch) {
 109                 case 'o': {
 110                         const char *p;
 111
 112                         for (p = keys = optarg; *p; ++p)
 113                                 if (!index(keylist, *p)) {
 114                                         (void)fprintf(stderr,
 115                                             "arithmetic: unknown key.\n");
 116                                         exit(1);
 117                                 }
 118                         nkeys = p - optarg;
 119                         break;
 120                 }
 121                 case 'r':
 122                         if ((rangemax = atoi(optarg)) <= 0) {
 123                                 (void)fprintf(stderr,
 124                                     "arithmetic: invalid range.\n");
 125                                 exit(1);
 126                         }
 127                         break;
 128                 case '?':
 129                 default:
 130                         usage();
 131                 }
 132         if (argc -= optind)
 133                 usage();
 134
 135         /* Seed the random-number generator. */
 136         srandomdev();
 137
 138         (void)signal(SIGINT, intr);
 139
 140         /* Now ask the questions. */
 141         for (;;) {
 142                 for (cnt = NQUESTS; cnt--;)
 143                         if (problem() == EOF)
 144                                 exit(0);
 145                 showstats();
 146         }
 147         /* NOTREACHED */
 148 }
 149
 150 /* Handle interrupt character.  Print score and exit. */
 151 void
 152 intr(__unused int sig)
 153 {
 154         showstats();
 155         exit(0);
 156 }
 157
 158 /* Print score.  Original `arithmetic' had a delay after printing it. */
 159 void
 160 showstats(void)
 161 {
 162         if (nright + nwrong > 0) {
 163                 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
 164                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 165                 if (nright > 0)
 166         (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 167                             (long)qtime, (float)qtime / nright);
 168         }
 169         (void)printf("\n");
 170 }
 171
 172 /*
 173  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 174  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 175  * selected such that the right operand and either the left operand (for +, x)
 176  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 177  * answer causes the numbers in the problem to be penalised, so that they are
 178  * more likely to appear in subsequent problems.
 179  */
 180 int
 181 problem(void)
 182 {
 183         char *p;
 184         time_t start, finish;
 185         int left, op, right, result;
 186         char line[80];
 187
 188         left = 0;
 189         right = 0;
 190         result = 0;
 191         op = keys[random() % nkeys];
 192         if (op != '/')
 193                 right = getrandom(rangemax + 1, op, 1);
 194 retry:
 195         /* Get the operands. */
 196         switch (op) {
 197         case '+':
 198                 left = getrandom(rangemax + 1, op, 0);
 199                 result = left + right;
 200                 break;
 201         case '-':
 202                 result = getrandom(rangemax + 1, op, 0);
 203                 left = right + result;
 204                 break;
 205         case 'x':
 206                 left = getrandom(rangemax + 1, op, 0);
 207                 result = left * right;
 208                 break;
 209         case '/':
 210                 right = getrandom(rangemax, op, 1) + 1;
 211                 result = getrandom(rangemax + 1, op, 0);
 212                 left = right * result + random() % right;
 213                 break;
 214         }
 215
 216         /*
 217          * A very big maxrange could cause negative values to pop
 218          * up, owing to overflow.
 219          */
 220         if (result < 0 || left < 0)
 221                 goto retry;
 222
 223         (void)printf("%d %c %d =   ", left, op, right);
 224         (void)fflush(stdout);
 225         (void)time(&start);
 226
 227         /*
 228          * Keep looping until the correct answer is given, or until EOF or
 229          * interrupt is typed.
 230          */
 231         for (;;) {
 232                 if (!fgets(line, sizeof(line), stdin)) {
 233                         (void)printf("\n");
 234                         return(EOF);
 235                 }
 236                 for (p = line; *p && isspace(*p); ++p);
 237                 if (!isdigit(*p)) {
 238                         (void)printf("Please type a number.\n");
 239                         continue;
 240                 }
 241                 if (atoi(p) == result) {
 242                         (void)printf("Right!\n");
 243                         ++nright;
 244                         break;
 245                 }
 246                 /* Wrong answer; penalise and ask again. */
 247                 (void)printf("What?\n");
 248                 ++nwrong;
 249                 penalise(right, op, 1);
 250                 if (op == 'x' || op == '+')
 251                         penalise(left, op, 0);
 252                 else
 253                         penalise(result, op, 0);
 254         }
 255
 256         /*
 257          * Accumulate the time taken.  Obviously rounding errors happen here;
 258          * however they should cancel out, because some of the time you are
 259          * charged for a partially elapsed second at the start, and some of
 260          * the time you are not charged for a partially elapsed second at the
 261          * end.
 262          */
 263         (void)time(&finish);
 264         qtime += finish - start;
 265         return(0);
 266 }
 267
 268 /*
 269  * Here is the code for accumulating penalties against the numbers for which
 270  * a wrong answer was given.  The right operand and either the left operand
 271  * (for +, x) or the result (for -, /) are stored in a list for the particular
 272  * operation, and each becomes more likely to appear again in that operation.
 273  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 274  * many extra chances of appearing.  Each time it is selected because of this,
 275  * its penalty is decreased by one; it is removed when it reaches 0.
 276  *
 277  * The penalty[] array gives the sum of all penalties in the list for
 278  * each operation and each operand.  The penlist[] array has the lists of
 279  * penalties themselves.
 280  */
 281
 282 int penalty[sizeof(keylist) - 1][2];
 283 struct penalty {
 284         int value, penalty;     /* Penalised value and its penalty. */
 285         struct penalty *next;
 286 } *penlist[sizeof(keylist) - 1][2];
 287
 288 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 289
 290 /*
 291  * Add a penalty for the number `value' to the list for operation `op',
 292  * operand number `operand' (0 or 1).  If we run out of memory, we just
 293  * forget about the penalty (how likely is this, anyway?).
 294  */
 295 void
 296 penalise(int value, int op, int operand)
 297 {
 298         struct penalty *p;
 299
 300         op = opnum(op);
 301         if ((p = malloc(sizeof(*p))) == NULL)
 302                 return;
 303         p->next = penlist[op][operand];
 304         penlist[op][operand] = p;
 305         penalty[op][operand] += p->penalty = WRONGPENALTY;
 306         p->value = value;
 307 }
 308
 309 /*
 310  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 311  * of operation `op'.  The random number we generate is either used directly
 312  * as a value, or represents a position in the penalty list.  If the latter,
 313  * we find the corresponding value and return that, decreasing its penalty.
 314  */
 315 int
 316 getrandom(int maxval, int op, int operand)
 317 {
 318         int value;
 319         struct penalty **pp, *p;
 320
 321         op = opnum(op);
 322         value = random() % (maxval + penalty[op][operand]);
 323
 324         /*
 325          * 0 to maxval - 1 is a number to be used directly; bigger values
 326          * are positions to be located in the penalty list.
 327          */
 328         if (value < maxval)
 329                 return(value);
 330         value -= maxval;
 331
 332         /*
 333          * Find the penalty at position `value'; decrement its penalty and
 334          * delete it if it reaches 0; return the corresponding value.
 335          */
 336         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 337                 if (p->penalty > value) {
 338                         value = p->value;
 339                         penalty[op][operand]--;
 340                         if (--(p->penalty) <= 0) {
 341                                 p = p->next;
 342                                 (void)free((char *)*pp);
 343                                 *pp = p;
 344                         }
 345                         return(value);
 346                 }
 347                 value -= p->penalty;
 348         }
 349         /*
 350          * We can only get here if the value from the penalty[] array doesn't
 351          * correspond to the actual sum of penalties in the list.  Provide an
 352          * obscure message.
 353          */
 354         (void)fprintf(stderr, "arithmetic: bug: inconsistent penalties\n");
 355         exit(1);
 356         /* NOTREACHED */
 357 }
 358
 359 /* Return an index for the character op, which is one of [+-x/]. */
 360 int
 361 opnum(int op)
 362 {
 363         char *p;
 364
 365         if (op == 0 || (p = index(keylist, op)) == NULL) {
 366                 (void)fprintf(stderr,
 367                     "arithmetic: bug: op %c not in keylist %s\n", op, keylist);
 368                 exit(1);
 369         }
 370         return(p - keylist);
 371 }
 372
 373 /* Print usage message and quit. */
 374 static void
 375 usage(void)
 376 {
 377         (void)fprintf(stderr, "usage: arithmetic [-o +-x/] [-r range]\n");
 378         exit(1);
 379 }