arithmetic/arithmetic.c

   1 /*      $NetBSD: arithmetic.c,v 1.14 2000/04/14 05:58:01 simonb 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 1.14 2000/04/14 05:58:01 simonb 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         int ch, cnt;
 122
 123         /* Revoke setgid privileges */
 124         setregid(getgid(), getgid());
 125
 126         while ((ch = getopt(argc, argv, "r:o:")) != -1)
 127                 switch(ch) {
 128                 case 'o': {
 129                         const char *p;
 130
 131                         for (p = keys = optarg; *p; ++p)
 132                                 if (!strchr(keylist, *p))
 133                                         errx(1, "arithmetic: unknown key.");
 134                         nkeys = p - optarg;
 135                         break;
 136                 }
 137                 case 'r':
 138                         if ((rangemax = atoi(optarg)) <= 0)
 139                                 errx(1, "arithmetic: invalid range.");
 140                         break;
 141                 case '?':
 142                 default:
 143                         usage();
 144                 }
 145         if (argc -= optind)
 146                 usage();
 147
 148         /* Seed the random-number generator. */
 149         srandom((int)time((time_t *)NULL));
 150
 151         (void)signal(SIGINT, intr);
 152
 153         /* Now ask the questions. */
 154         for (;;) {
 155                 for (cnt = NQUESTS; cnt--;)
 156                         if (problem() == EOF)
 157                                 exit(0);
 158                 showstats();
 159         }
 160         /* NOTREACHED */
 161 }
 162
 163 /* Handle interrupt character.  Print score and exit. */
 164 void
 165 intr(dummy)
 166         int dummy __attribute__((__unused__));
 167 {
 168         showstats();
 169         exit(0);
 170 }
 171
 172 /* Print score.  Original `arithmetic' had a delay after printing it. */
 173 void
 174 showstats()
 175 {
 176         if (nright + nwrong > 0) {
 177                 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
 178                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 179                 if (nright > 0)
 180         (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 181                             (long)qtime, (float)qtime / nright);
 182         }
 183         (void)printf("\n");
 184 }
 185
 186 /*
 187  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 188  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 189  * selected such that the right operand and either the left operand (for +, x)
 190  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 191  * answer causes the numbers in the problem to be penalised, so that they are
 192  * more likely to appear in subsequent problems.
 193  */
 194 int
 195 problem()
 196 {
 197         char *p;
 198         time_t start, finish;
 199         int left, op, right, result;
 200         char line[80];
 201
 202         right = left = result = 0;
 203         op = keys[random() % nkeys];
 204         if (op != '/')
 205                 right = getrandom(rangemax + 1, op, 1);
 206 retry:
 207         /* Get the operands. */
 208         switch (op) {
 209         case '+':
 210                 left = getrandom(rangemax + 1, op, 0);
 211                 result = left + right;
 212                 break;
 213         case '-':
 214                 result = getrandom(rangemax + 1, op, 0);
 215                 left = right + result;
 216                 break;
 217         case 'x':
 218                 left = getrandom(rangemax + 1, op, 0);
 219                 result = left * right;
 220                 break;
 221         case '/':
 222                 right = getrandom(rangemax, op, 1) + 1;
 223                 result = getrandom(rangemax + 1, op, 0);
 224                 left = right * result + random() % right;
 225                 break;
 226         }
 227
 228         /*
 229          * A very big maxrange could cause negative values to pop
 230          * up, owing to overflow.
 231          */
 232         if (result < 0 || left < 0)
 233                 goto retry;
 234
 235         (void)printf("%d %c %d =   ", left, op, right);
 236         (void)fflush(stdout);
 237         (void)time(&start);
 238
 239         /*
 240          * Keep looping until the correct answer is given, or until EOF or
 241          * interrupt is typed.
 242          */
 243         for (;;) {
 244                 if (!fgets(line, sizeof(line), stdin)) {
 245                         (void)printf("\n");
 246                         return(EOF);
 247                 }
 248                 for (p = line; *p && isspace(*p); ++p);
 249                 if (!isdigit(*p)) {
 250                         (void)printf("Please type a number.\n");
 251                         continue;
 252                 }
 253                 if (atoi(p) == result) {
 254                         (void)printf("Right!\n");
 255                         ++nright;
 256                         break;
 257                 }
 258                 /* Wrong answer; penalise and ask again. */
 259                 (void)printf("What?\n");
 260                 ++nwrong;
 261                 penalise(right, op, 1);
 262                 if (op == 'x' || op == '+')
 263                         penalise(left, op, 0);
 264                 else
 265                         penalise(result, op, 0);
 266         }
 267
 268         /*
 269          * Accumulate the time taken.  Obviously rounding errors happen here;
 270          * however they should cancel out, because some of the time you are
 271          * charged for a partially elapsed second at the start, and some of
 272          * the time you are not charged for a partially elapsed second at the
 273          * end.
 274          */
 275         (void)time(&finish);
 276         qtime += finish - start;
 277         return(0);
 278 }
 279
 280 /*
 281  * Here is the code for accumulating penalties against the numbers for which
 282  * a wrong answer was given.  The right operand and either the left operand
 283  * (for +, x) or the result (for -, /) are stored in a list for the particular
 284  * operation, and each becomes more likely to appear again in that operation.
 285  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 286  * many extra chances of appearing.  Each time it is selected because of this,
 287  * its penalty is decreased by one; it is removed when it reaches 0.
 288  *
 289  * The penalty[] array gives the sum of all penalties in the list for
 290  * each operation and each operand.  The penlist[] array has the lists of
 291  * penalties themselves.
 292  */
 293
 294 int penalty[sizeof(keylist) - 1][2];
 295 struct penalty {
 296         int value, penalty;     /* Penalised value and its penalty. */
 297         struct penalty *next;
 298 } *penlist[sizeof(keylist) - 1][2];
 299
 300 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 301
 302 /*
 303  * Add a penalty for the number `value' to the list for operation `op',
 304  * operand number `operand' (0 or 1).  If we run out of memory, we just
 305  * forget about the penalty (how likely is this, anyway?).
 306  */
 307 void
 308 penalise(value, op, operand)
 309         int value, op, operand;
 310 {
 311         struct penalty *p;
 312
 313         op = opnum(op);
 314         if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL)
 315                 return;
 316         p->next = penlist[op][operand];
 317         penlist[op][operand] = p;
 318         penalty[op][operand] += p->penalty = WRONGPENALTY;
 319         p->value = value;
 320 }
 321
 322 /*
 323  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 324  * of operation `op'.  The random number we generate is either used directly
 325  * as a value, or represents a position in the penalty list.  If the latter,
 326  * we find the corresponding value and return that, decreasing its penalty.
 327  */
 328 int
 329 getrandom(maxval, op, operand)
 330         int maxval, op, operand;
 331 {
 332         int value;
 333         struct penalty **pp, *p;
 334
 335         op = opnum(op);
 336         value = random() % (maxval + penalty[op][operand]);
 337
 338         /*
 339          * 0 to maxval - 1 is a number to be used directly; bigger values
 340          * are positions to be located in the penalty list.
 341          */
 342         if (value < maxval)
 343                 return(value);
 344         value -= maxval;
 345
 346         /*
 347          * Find the penalty at position `value'; decrement its penalty and
 348          * delete it if it reaches 0; return the corresponding value.
 349          */
 350         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 351                 if (p->penalty > value) {
 352                         value = p->value;
 353                         penalty[op][operand]--;
 354                         if (--(p->penalty) <= 0) {
 355                                 p = p->next;
 356                                 (void)free((char *)*pp);
 357                                 *pp = p;
 358                         }
 359                         return(value);
 360                 }
 361                 value -= p->penalty;
 362         }
 363         /*
 364          * We can only get here if the value from the penalty[] array doesn't
 365          * correspond to the actual sum of penalties in the list.  Provide an
 366          * obscure message.
 367          */
 368         errx(1, "arithmetic: bug: inconsistent penalties.");
 369         /* NOTREACHED */
 370 }
 371
 372 /* Return an index for the character op, which is one of [+-x/]. */
 373 int
 374 opnum(op)
 375         int op;
 376 {
 377         char *p;
 378
 379         if (op == 0 || (p = strchr(keylist, op)) == NULL)
 380                 errx(1, "arithmetic: bug: op %c not in keylist %s",
 381                     op, keylist);
 382         return(p - keylist);
 383 }
 384
 385 /* Print usage message and quit. */
 386 void
 387 usage()
 388 {
 389         extern char *__progname;        /* from crt0.o */
 390
 391         (void)fprintf(stderr, "usage: %s [-o +-x/] [-r range]\n",
 392                 __progname);
 393         exit(1);
 394 }