arithmetic/arithmetic.c

   1 /*      $NetBSD: arithmetic.c,v 1.21 2004/11/05 21:30:31 dsl 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. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include <sys/cdefs.h>
  36 #ifndef lint
  37 __COPYRIGHT("@(#) Copyright (c) 1989, 1993\n\
  38         The Regents of the University of California.  All rights reserved.\n");
  39 #endif /* not lint */
  40
  41 #ifndef lint
  42 #if 0
  43 static char sccsid[] = "@(#)arithmetic.c        8.1 (Berkeley) 5/31/93";
  44 #else
  45 __RCSID("$NetBSD: arithmetic.c,v 1.21 2004/11/05 21:30:31 dsl Exp $");
  46 #endif
  47 #endif /* not lint */
  48
  49 /*
  50  * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
  51  *
  52  * The operation of this program mimics that of the standard Unix game
  53  * `arithmetic'.  I've made it as close as I could manage without examining
  54  * the source code.  The principal differences are:
  55  *
  56  * The method of biasing towards numbers that had wrong answers in the past
  57  * is different; original `arithmetic' seems to retain the bias forever,
  58  * whereas this program lets the bias gradually decay as it is used.
  59  *
  60  * Original `arithmetic' delays for some period (3 seconds?) after printing
  61  * the score.  I saw no reason for this delay, so I scrapped it.
  62  *
  63  * There is no longer a limitation on the maximum range that can be supplied
  64  * to the program.  The original program required it to be less than 100.
  65  * Anomalous results may occur with this program if ranges big enough to
  66  * allow overflow are given.
  67  *
  68  * I have obviously not attempted to duplicate bugs in the original.  It
  69  * would go into an infinite loop if invoked as `arithmetic / 0'.  It also
  70  * did not recognise an EOF in its input, and would continue trying to read
  71  * after it.  It did not check that the input was a valid number, treating any
  72  * garbage as 0.  Finally, it did not flush stdout after printing its prompt,
  73  * so in the unlikely event that stdout was not a terminal, it would not work
  74  * properly.
  75  */
  76
  77 #include <sys/types.h>
  78 #include <err.h>
  79 #include <ctype.h>
  80 #include <signal.h>
  81 #include <stdio.h>
  82 #include <stdlib.h>
  83 #include <string.h>
  84 #include <time.h>
  85 #include <unistd.h>
  86
  87 int     getrandom(int, int, int);
  88 void    intr(int) __attribute__((__noreturn__));
  89 int     main(int, char *[]);
  90 int     opnum(int);
  91 void    penalise(int, int, int);
  92 int     problem(void);
  93 void    showstats(int);
  94 void    usage(void) __attribute__((__noreturn__));
  95
  96 const char keylist[] = "+-x/";
  97 const char defaultkeys[] = "+-";
  98 const char *keys = defaultkeys;
  99 int nkeys = sizeof(defaultkeys) - 1;
 100 int rangemax = 10;
 101 int nright, nwrong;
 102 time_t qtime;
 103 #define NQUESTS 20
 104
 105 /*
 106  * Select keys from +-x/ to be asked addition, subtraction, multiplication,
 107  * and division problems.  More than one key may be given.  The default is
 108  * +-.  Specify a range to confine the operands to 0 - range.  Default upper
 109  * bound is 10.  After every NQUESTS questions, statistics on the performance
 110  * so far are printed.
 111  */
 112 int
 113 main(argc, argv)
 114         int argc;
 115         char **argv;
 116 {
 117         int ch, cnt;
 118
 119         /* Revoke setgid privileges */
 120         setgid(getgid());
 121
 122         while ((ch = getopt(argc, argv, "r:o:")) != -1)
 123                 switch(ch) {
 124                 case 'o': {
 125                         const char *p;
 126
 127                         for (p = keys = optarg; *p; ++p)
 128                                 if (!strchr(keylist, *p))
 129                                         errx(1, "arithmetic: unknown key.");
 130                         nkeys = p - optarg;
 131                         break;
 132                 }
 133                 case 'r':
 134                         if ((rangemax = atoi(optarg)) <= 0)
 135                                 errx(1, "arithmetic: invalid range.");
 136                         break;
 137                 case '?':
 138                 default:
 139                         usage();
 140                 }
 141         if (argc -= optind)
 142                 usage();
 143
 144         /* Seed the random-number generator. */
 145         srandom((int)time((time_t *)NULL));
 146
 147         (void)signal(SIGINT, intr);
 148
 149         /* Now ask the questions. */
 150         for (;;) {
 151                 for (cnt = NQUESTS; cnt--;)
 152                         if (problem() == EOF)
 153                                 exit(0);
 154                 showstats(0);
 155         }
 156         /* NOTREACHED */
 157 }
 158
 159 /* Handle interrupt character.  Print score and exit. */
 160 void
 161 intr(dummy)
 162         int dummy __attribute__((__unused__));
 163 {
 164         showstats(1);
 165         exit(0);
 166 }
 167
 168 /* Print score.  Original `arithmetic' had a delay after printing it. */
 169 void
 170 showstats(bool_sigint)
 171         int bool_sigint;
 172 {
 173         if (nright + nwrong > 0) {
 174                 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
 175                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 176                 if (nright > 0)
 177         (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 178                             (long)qtime, (float)qtime / nright);
 179         }
 180         if(!bool_sigint) {
 181                 (void)printf("Press RETURN to continue...\n");
 182                 while(!getchar()) ;
 183         }
 184         (void)printf("\n");
 185 }
 186
 187 /*
 188  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 189  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 190  * selected such that the right operand and either the left operand (for +, x)
 191  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 192  * answer causes the numbers in the problem to be penalised, so that they are
 193  * more likely to appear in subsequent problems.
 194  */
 195 int
 196 problem()
 197 {
 198         char *p;
 199         time_t start, finish;
 200         int left, op, right, result;
 201         char line[80];
 202
 203         right = left = result = 0;
 204         op = keys[random() % nkeys];
 205         if (op != '/')
 206                 right = getrandom(rangemax + 1, op, 1);
 207 retry:
 208         /* Get the operands. */
 209         switch (op) {
 210         case '+':
 211                 left = getrandom(rangemax + 1, op, 0);
 212                 result = left + right;
 213                 break;
 214         case '-':
 215                 result = getrandom(rangemax + 1, op, 0);
 216                 left = right + result;
 217                 break;
 218         case 'x':
 219                 left = getrandom(rangemax + 1, op, 0);
 220                 result = left * right;
 221                 break;
 222         case '/':
 223                 right = getrandom(rangemax, op, 1) + 1;
 224                 result = getrandom(rangemax + 1, op, 0);
 225                 left = right * result + random() % right;
 226                 break;
 227         }
 228
 229         /*
 230          * A very big maxrange could cause negative values to pop
 231          * up, owing to overflow.
 232          */
 233         if (result < 0 || left < 0)
 234                 goto retry;
 235
 236         (void)printf("%d %c %d =   ", left, op, right);
 237         (void)fflush(stdout);
 238         (void)time(&start);
 239
 240         /*
 241          * Keep looping until the correct answer is given, or until EOF or
 242          * interrupt is typed.
 243          */
 244         for (;;) {
 245                 if (!fgets(line, sizeof(line), stdin)) {
 246                         (void)printf("\n");
 247                         return(EOF);
 248                 }
 249                 for (p = line; *p && isspace((unsigned char)*p); ++p);
 250                 if (!isdigit((unsigned char)*p)) {
 251                         (void)printf("Please type a number.\n");
 252                         continue;
 253                 }
 254                 if (atoi(p) == result) {
 255                         (void)printf("Right!\n");
 256                         ++nright;
 257                         break;
 258                 }
 259                 /* Wrong answer; penalise and ask again. */
 260                 (void)printf("What?\n");
 261                 ++nwrong;
 262                 penalise(right, op, 1);
 263                 if (op == 'x' || op == '+')
 264                         penalise(left, op, 0);
 265                 else
 266                         penalise(result, op, 0);
 267         }
 268
 269         /*
 270          * Accumulate the time taken.  Obviously rounding errors happen here;
 271          * however they should cancel out, because some of the time you are
 272          * charged for a partially elapsed second at the start, and some of
 273          * the time you are not charged for a partially elapsed second at the
 274          * end.
 275          */
 276         (void)time(&finish);
 277         qtime += finish - start;
 278         return(0);
 279 }
 280
 281 /*
 282  * Here is the code for accumulating penalties against the numbers for which
 283  * a wrong answer was given.  The right operand and either the left operand
 284  * (for +, x) or the result (for -, /) are stored in a list for the particular
 285  * operation, and each becomes more likely to appear again in that operation.
 286  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 287  * many extra chances of appearing.  Each time it is selected because of this,
 288  * its penalty is decreased by one; it is removed when it reaches 0.
 289  *
 290  * The penalty[] array gives the sum of all penalties in the list for
 291  * each operation and each operand.  The penlist[] array has the lists of
 292  * penalties themselves.
 293  */
 294
 295 int penalty[sizeof(keylist) - 1][2];
 296 struct penalty {
 297         int value, penalty;     /* Penalised value and its penalty. */
 298         struct penalty *next;
 299 } *penlist[sizeof(keylist) - 1][2];
 300
 301 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 302
 303 /*
 304  * Add a penalty for the number `value' to the list for operation `op',
 305  * operand number `operand' (0 or 1).  If we run out of memory, we just
 306  * forget about the penalty (how likely is this, anyway?).
 307  */
 308 void
 309 penalise(value, op, operand)
 310         int value, op, operand;
 311 {
 312         struct penalty *p;
 313
 314         op = opnum(op);
 315         if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL)
 316                 return;
 317         p->next = penlist[op][operand];
 318         penlist[op][operand] = p;
 319         penalty[op][operand] += p->penalty = WRONGPENALTY;
 320         p->value = value;
 321 }
 322
 323 /*
 324  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 325  * of operation `op'.  The random number we generate is either used directly
 326  * as a value, or represents a position in the penalty list.  If the latter,
 327  * we find the corresponding value and return that, decreasing its penalty.
 328  */
 329 int
 330 getrandom(maxval, op, operand)
 331         int maxval, op, operand;
 332 {
 333         int value;
 334         struct penalty **pp, *p;
 335
 336         op = opnum(op);
 337         value = random() % (maxval + penalty[op][operand]);
 338
 339         /*
 340          * 0 to maxval - 1 is a number to be used directly; bigger values
 341          * are positions to be located in the penalty list.
 342          */
 343         if (value < maxval)
 344                 return(value);
 345         value -= maxval;
 346
 347         /*
 348          * Find the penalty at position `value'; decrement its penalty and
 349          * delete it if it reaches 0; return the corresponding value.
 350          */
 351         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 352                 if (p->penalty > value) {
 353                         value = p->value;
 354                         penalty[op][operand]--;
 355                         if (--(p->penalty) <= 0) {
 356                                 p = p->next;
 357                                 (void)free((char *)*pp);
 358                                 *pp = p;
 359                         }
 360                         return(value);
 361                 }
 362                 value -= p->penalty;
 363         }
 364         /*
 365          * We can only get here if the value from the penalty[] array doesn't
 366          * correspond to the actual sum of penalties in the list.  Provide an
 367          * obscure message.
 368          */
 369         errx(1, "arithmetic: bug: inconsistent penalties.");
 370         /* NOTREACHED */
 371 }
 372
 373 /* Return an index for the character op, which is one of [+-x/]. */
 374 int
 375 opnum(op)
 376         int op;
 377 {
 378         char *p;
 379
 380         if (op == 0 || (p = strchr(keylist, op)) == NULL)
 381                 errx(1, "arithmetic: bug: op %c not in keylist %s",
 382                     op, keylist);
 383         return(p - keylist);
 384 }
 385
 386 /* Print usage message and quit. */
 387 void
 388 usage()
 389 {
 390         (void)fprintf(stderr, "Usage: %s [-o +-x/] [-r range]\n",
 391                 getprogname());
 392         exit(1);
 393 }