arithmetic/arithmetic.c

   1 /*      $NetBSD: arithmetic.c,v 1.13 1999/07/17 19:11:30 hubertf Exp $  */
   2
   3 /*
   4  * Copyright (c) 1989, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * Eamonn McManus of Trinity College Dublin.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. All advertising materials mentioning features or use of this software
  19  *    must display the following acknowledgement:
  20  *      This product includes software developed by the University of
  21  *      California, Berkeley and its contributors.
  22  * 4. Neither the name of the University nor the names of its contributors
  23  *    may be used to endorse or promote products derived from this software
  24  *    without specific prior written permission.
  25  *
  26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  36  * SUCH DAMAGE.
  37  */
  38
  39 #include <sys/cdefs.h>
  40 #ifndef lint
  41 __COPYRIGHT("@(#) Copyright (c) 1989, 1993\n\
  42         The Regents of the University of California.  All rights reserved.\n");
  43 #endif /* not lint */
  44
  45 #ifndef lint
  46 #if 0
  47 static char sccsid[] = "@(#)arithmetic.c        8.1 (Berkeley) 5/31/93";
  48 #else
  49 __RCSID("$NetBSD: arithmetic.c,v 1.13 1999/07/17 19:11:30 hubertf Exp $");
  50 #endif
  51 #endif /* not lint */
  52
  53 /*
  54  * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
  55  *
  56  * The operation of this program mimics that of the standard Unix game
  57  * `arithmetic'.  I've made it as close as I could manage without examining
  58  * the source code.  The principal differences are:
  59  *
  60  * The method of biasing towards numbers that had wrong answers in the past
  61  * is different; original `arithmetic' seems to retain the bias forever,
  62  * whereas this program lets the bias gradually decay as it is used.
  63  *
  64  * Original `arithmetic' delays for some period (3 seconds?) after printing
  65  * the score.  I saw no reason for this delay, so I scrapped it.
  66  *
  67  * There is no longer a limitation on the maximum range that can be supplied
  68  * to the program.  The original program required it to be less than 100.
  69  * Anomalous results may occur with this program if ranges big enough to
  70  * allow overflow are given.
  71  *
  72  * I have obviously not attempted to duplicate bugs in the original.  It
  73  * would go into an infinite loop if invoked as `arithmetic / 0'.  It also
  74  * did not recognise an EOF in its input, and would continue trying to read
  75  * after it.  It did not check that the input was a valid number, treating any
  76  * garbage as 0.  Finally, it did not flush stdout after printing its prompt,
  77  * so in the unlikely event that stdout was not a terminal, it would not work
  78  * properly.
  79  */
  80
  81 #include <sys/types.h>
  82 #include <err.h>
  83 #include <ctype.h>
  84 #include <signal.h>
  85 #include <stdio.h>
  86 #include <stdlib.h>
  87 #include <string.h>
  88 #include <time.h>
  89 #include <unistd.h>
  90
  91 int     getrandom __P((int, int, int));
  92 void    intr __P((int)) __attribute__((__noreturn__));
  93 int     main __P((int, char *[]));
  94 int     opnum __P((int));
  95 void    penalise __P((int, int, int));
  96 int     problem __P((void));
  97 void    showstats __P((void));
  98 void    usage __P((void)) __attribute__((__noreturn__));
  99
 100 const char keylist[] = "+-x/";
 101 const char defaultkeys[] = "+-";
 102 const char *keys = defaultkeys;
 103 int nkeys = sizeof(defaultkeys) - 1;
 104 int rangemax = 10;
 105 int nright, nwrong;
 106 time_t qtime;
 107 #define NQUESTS 20
 108
 109 /*
 110  * Select keys from +-x/ to be asked addition, subtraction, multiplication,
 111  * and division problems.  More than one key may be given.  The default is
 112  * +-.  Specify a range to confine the operands to 0 - range.  Default upper
 113  * bound is 10.  After every NQUESTS questions, statistics on the performance
 114  * so far are printed.
 115  */
 116 int
 117 main(argc, argv)
 118         int argc;
 119         char **argv;
 120 {
 121         extern char *optarg;
 122         extern int optind;
 123         int ch, cnt;
 124
 125         /* Revoke setgid privileges */
 126         setregid(getgid(), getgid());
 127
 128         while ((ch = getopt(argc, argv, "r:o:")) != -1)
 129                 switch(ch) {
 130                 case 'o': {
 131                         const char *p;
 132
 133                         for (p = keys = optarg; *p; ++p)
 134                                 if (!strchr(keylist, *p))
 135                                         errx(1, "arithmetic: unknown key.");
 136                         nkeys = p - optarg;
 137                         break;
 138                 }
 139                 case 'r':
 140                         if ((rangemax = atoi(optarg)) <= 0)
 141                                 errx(1, "arithmetic: invalid range.");
 142                         break;
 143                 case '?':
 144                 default:
 145                         usage();
 146                 }
 147         if (argc -= optind)
 148                 usage();
 149
 150         /* Seed the random-number generator. */
 151         srandom((int)time((time_t *)NULL));
 152
 153         (void)signal(SIGINT, intr);
 154
 155         /* Now ask the questions. */
 156         for (;;) {
 157                 for (cnt = NQUESTS; cnt--;)
 158                         if (problem() == EOF)
 159                                 exit(0);
 160                 showstats();
 161         }
 162         /* NOTREACHED */
 163 }
 164
 165 /* Handle interrupt character.  Print score and exit. */
 166 void
 167 intr(dummy)
 168         int dummy __attribute__((__unused__));
 169 {
 170         showstats();
 171         exit(0);
 172 }
 173
 174 /* Print score.  Original `arithmetic' had a delay after printing it. */
 175 void
 176 showstats()
 177 {
 178         if (nright + nwrong > 0) {
 179                 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
 180                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 181                 if (nright > 0)
 182         (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 183                             (long)qtime, (float)qtime / nright);
 184         }
 185         (void)printf("\n");
 186 }
 187
 188 /*
 189  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 190  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 191  * selected such that the right operand and either the left operand (for +, x)
 192  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 193  * answer causes the numbers in the problem to be penalised, so that they are
 194  * more likely to appear in subsequent problems.
 195  */
 196 int
 197 problem()
 198 {
 199         char *p;
 200         time_t start, finish;
 201         int left, op, right, result;
 202         char line[80];
 203
 204         right = left = result = 0;
 205         op = keys[random() % nkeys];
 206         if (op != '/')
 207                 right = getrandom(rangemax + 1, op, 1);
 208 retry:
 209         /* Get the operands. */
 210         switch (op) {
 211         case '+':
 212                 left = getrandom(rangemax + 1, op, 0);
 213                 result = left + right;
 214                 break;
 215         case '-':
 216                 result = getrandom(rangemax + 1, op, 0);
 217                 left = right + result;
 218                 break;
 219         case 'x':
 220                 left = getrandom(rangemax + 1, op, 0);
 221                 result = left * right;
 222                 break;
 223         case '/':
 224                 right = getrandom(rangemax, op, 1) + 1;
 225                 result = getrandom(rangemax + 1, op, 0);
 226                 left = right * result + random() % right;
 227                 break;
 228         }
 229
 230         /*
 231          * A very big maxrange could cause negative values to pop
 232          * up, owing to overflow.
 233          */
 234         if (result < 0 || left < 0)
 235                 goto retry;
 236
 237         (void)printf("%d %c %d =   ", left, op, right);
 238         (void)fflush(stdout);
 239         (void)time(&start);
 240
 241         /*
 242          * Keep looping until the correct answer is given, or until EOF or
 243          * interrupt is typed.
 244          */
 245         for (;;) {
 246                 if (!fgets(line, sizeof(line), stdin)) {
 247                         (void)printf("\n");
 248                         return(EOF);
 249                 }
 250                 for (p = line; *p && isspace(*p); ++p);
 251                 if (!isdigit(*p)) {
 252                         (void)printf("Please type a number.\n");
 253                         continue;
 254                 }
 255                 if (atoi(p) == result) {
 256                         (void)printf("Right!\n");
 257                         ++nright;
 258                         break;
 259                 }
 260                 /* Wrong answer; penalise and ask again. */
 261                 (void)printf("What?\n");
 262                 ++nwrong;
 263                 penalise(right, op, 1);
 264                 if (op == 'x' || op == '+')
 265                         penalise(left, op, 0);
 266                 else
 267                         penalise(result, op, 0);
 268         }
 269
 270         /*
 271          * Accumulate the time taken.  Obviously rounding errors happen here;
 272          * however they should cancel out, because some of the time you are
 273          * charged for a partially elapsed second at the start, and some of
 274          * the time you are not charged for a partially elapsed second at the
 275          * end.
 276          */
 277         (void)time(&finish);
 278         qtime += finish - start;
 279         return(0);
 280 }
 281
 282 /*
 283  * Here is the code for accumulating penalties against the numbers for which
 284  * a wrong answer was given.  The right operand and either the left operand
 285  * (for +, x) or the result (for -, /) are stored in a list for the particular
 286  * operation, and each becomes more likely to appear again in that operation.
 287  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 288  * many extra chances of appearing.  Each time it is selected because of this,
 289  * its penalty is decreased by one; it is removed when it reaches 0.
 290  *
 291  * The penalty[] array gives the sum of all penalties in the list for
 292  * each operation and each operand.  The penlist[] array has the lists of
 293  * penalties themselves.
 294  */
 295
 296 int penalty[sizeof(keylist) - 1][2];
 297 struct penalty {
 298         int value, penalty;     /* Penalised value and its penalty. */
 299         struct penalty *next;
 300 } *penlist[sizeof(keylist) - 1][2];
 301
 302 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 303
 304 /*
 305  * Add a penalty for the number `value' to the list for operation `op',
 306  * operand number `operand' (0 or 1).  If we run out of memory, we just
 307  * forget about the penalty (how likely is this, anyway?).
 308  */
 309 void
 310 penalise(value, op, operand)
 311         int value, op, operand;
 312 {
 313         struct penalty *p;
 314
 315         op = opnum(op);
 316         if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL)
 317                 return;
 318         p->next = penlist[op][operand];
 319         penlist[op][operand] = p;
 320         penalty[op][operand] += p->penalty = WRONGPENALTY;
 321         p->value = value;
 322 }
 323
 324 /*
 325  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 326  * of operation `op'.  The random number we generate is either used directly
 327  * as a value, or represents a position in the penalty list.  If the latter,
 328  * we find the corresponding value and return that, decreasing its penalty.
 329  */
 330 int
 331 getrandom(maxval, op, operand)
 332         int maxval, op, operand;
 333 {
 334         int value;
 335         struct penalty **pp, *p;
 336
 337         op = opnum(op);
 338         value = random() % (maxval + penalty[op][operand]);
 339
 340         /*
 341          * 0 to maxval - 1 is a number to be used directly; bigger values
 342          * are positions to be located in the penalty list.
 343          */
 344         if (value < maxval)
 345                 return(value);
 346         value -= maxval;
 347
 348         /*
 349          * Find the penalty at position `value'; decrement its penalty and
 350          * delete it if it reaches 0; return the corresponding value.
 351          */
 352         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 353                 if (p->penalty > value) {
 354                         value = p->value;
 355                         penalty[op][operand]--;
 356                         if (--(p->penalty) <= 0) {
 357                                 p = p->next;
 358                                 (void)free((char *)*pp);
 359                                 *pp = p;
 360                         }
 361                         return(value);
 362                 }
 363                 value -= p->penalty;
 364         }
 365         /*
 366          * We can only get here if the value from the penalty[] array doesn't
 367          * correspond to the actual sum of penalties in the list.  Provide an
 368          * obscure message.
 369          */
 370         errx(1, "arithmetic: bug: inconsistent penalties.");
 371         /* NOTREACHED */
 372 }
 373
 374 /* Return an index for the character op, which is one of [+-x/]. */
 375 int
 376 opnum(op)
 377         int op;
 378 {
 379         char *p;
 380
 381         if (op == 0 || (p = strchr(keylist, op)) == NULL)
 382                 errx(1, "arithmetic: bug: op %c not in keylist %s",
 383                     op, keylist);
 384         return(p - keylist);
 385 }
 386
 387 /* Print usage message and quit. */
 388 void
 389 usage()
 390 {
 391         extern char *__progname;        /* from crt0.o */
 392
 393         (void)fprintf(stderr, "usage: %s [-o +-x/] [-r range]\n",
 394                 __progname);
 395         exit(1);
 396 }