arithmetic/arithmetic.c

   1 /*      $NetBSD: arithmetic.c,v 1.5 1995/03/21 11:59:32 cgd 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 #ifndef lint
  40 static char copyright[] =
  41 "@(#) 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 static char rcsid[] = "$NetBSD: arithmetic.c,v 1.5 1995/03/21 11:59:32 cgd 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 <signal.h>
  83 #include <ctype.h>
  84 #include <stdio.h>
  85 #include <string.h>
  86 #include <time.h>
  87
  88 char keylist[] = "+-x/";
  89 char defaultkeys[] = "+-";
  90 char *keys = defaultkeys;
  91 int nkeys = sizeof(defaultkeys) - 1;
  92 int rangemax = 10;
  93 int nright, nwrong;
  94 time_t qtime;
  95 #define NQUESTS 20
  96
  97 /*
  98  * Select keys from +-x/ to be asked addition, subtraction, multiplication,
  99  * and division problems.  More than one key may be given.  The default is
 100  * +-.  Specify a range to confine the operands to 0 - range.  Default upper
 101  * bound is 10.  After every NQUESTS questions, statistics on the performance
 102  * so far are printed.
 103  */
 104 void
 105 main(argc, argv)
 106         int argc;
 107         char **argv;
 108 {
 109         extern char *optarg;
 110         extern int optind;
 111         int ch, cnt;
 112         void intr();
 113
 114         while ((ch = getopt(argc, argv, "r:o:")) != EOF)
 115                 switch(ch) {
 116                 case 'o': {
 117                         register char *p;
 118
 119                         for (p = keys = optarg; *p; ++p)
 120                                 if (!index(keylist, *p)) {
 121                                         (void)fprintf(stderr,
 122                                             "arithmetic: unknown key.\n");
 123                                         exit(1);
 124                                 }
 125                         nkeys = p - optarg;
 126                         break;
 127                 }
 128                 case 'r':
 129                         if ((rangemax = atoi(optarg)) <= 0) {
 130                                 (void)fprintf(stderr,
 131                                     "arithmetic: invalid range.\n");
 132                                 exit(1);
 133                         }
 134                         break;
 135                 case '?':
 136                 default:
 137                         usage();
 138                 }
 139         if (argc -= optind)
 140                 usage();
 141
 142         /* Seed the random-number generator. */
 143         srandom((int)time((time_t *)NULL));
 144
 145         (void)signal(SIGINT, intr);
 146
 147         /* Now ask the questions. */
 148         for (;;) {
 149                 for (cnt = NQUESTS; cnt--;)
 150                         if (problem() == EOF)
 151                                 exit(0);
 152                 showstats();
 153         }
 154         /* NOTREACHED */
 155 }
 156
 157 /* Handle interrupt character.  Print score and exit. */
 158 void
 159 intr()
 160 {
 161         showstats();
 162         exit(0);
 163 }
 164
 165 /* Print score.  Original `arithmetic' had a delay after printing it. */
 166 showstats()
 167 {
 168         if (nright + nwrong > 0) {
 169                 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
 170                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 171                 if (nright > 0)
 172         (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 173                             (long)qtime, (float)qtime / nright);
 174         }
 175         (void)printf("\n");
 176 }
 177
 178 /*
 179  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 180  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 181  * selected such that the right operand and either the left operand (for +, x)
 182  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 183  * answer causes the numbers in the problem to be penalised, so that they are
 184  * more likely to appear in subsequent problems.
 185  */
 186 problem()
 187 {
 188         register char *p;
 189         time_t start, finish;
 190         int left, op, right, result;
 191         char line[80];
 192
 193         op = keys[random() % nkeys];
 194         if (op != '/')
 195                 right = getrandom(rangemax + 1, op, 1);
 196 retry:
 197         /* Get the operands. */
 198         switch (op) {
 199         case '+':
 200                 left = getrandom(rangemax + 1, op, 0);
 201                 result = left + right;
 202                 break;
 203         case '-':
 204                 result = getrandom(rangemax + 1, op, 0);
 205                 left = right + result;
 206                 break;
 207         case 'x':
 208                 left = getrandom(rangemax + 1, op, 0);
 209                 result = left * right;
 210                 break;
 211         case '/':
 212                 right = getrandom(rangemax, op, 1) + 1;
 213                 result = getrandom(rangemax + 1, op, 0);
 214                 left = right * result + random() % right;
 215                 break;
 216         }
 217
 218         /*
 219          * A very big maxrange could cause negative values to pop
 220          * up, owing to overflow.
 221          */
 222         if (result < 0 || left < 0)
 223                 goto retry;
 224
 225         (void)printf("%d %c %d =   ", left, op, right);
 226         (void)fflush(stdout);
 227         (void)time(&start);
 228
 229         /*
 230          * Keep looping until the correct answer is given, or until EOF or
 231          * interrupt is typed.
 232          */
 233         for (;;) {
 234                 if (!fgets(line, sizeof(line), stdin)) {
 235                         (void)printf("\n");
 236                         return(EOF);
 237                 }
 238                 for (p = line; *p && isspace(*p); ++p);
 239                 if (!isdigit(*p)) {
 240                         (void)printf("Please type a number.\n");
 241                         continue;
 242                 }
 243                 if (atoi(p) == result) {
 244                         (void)printf("Right!\n");
 245                         ++nright;
 246                         break;
 247                 }
 248                 /* Wrong answer; penalise and ask again. */
 249                 (void)printf("What?\n");
 250                 ++nwrong;
 251                 penalise(right, op, 1);
 252                 if (op == 'x' || op == '+')
 253                         penalise(left, op, 0);
 254                 else
 255                         penalise(result, op, 0);
 256         }
 257
 258         /*
 259          * Accumulate the time taken.  Obviously rounding errors happen here;
 260          * however they should cancel out, because some of the time you are
 261          * charged for a partially elapsed second at the start, and some of
 262          * the time you are not charged for a partially elapsed second at the
 263          * end.
 264          */
 265         (void)time(&finish);
 266         qtime += finish - start;
 267         return(0);
 268 }
 269
 270 /*
 271  * Here is the code for accumulating penalties against the numbers for which
 272  * a wrong answer was given.  The right operand and either the left operand
 273  * (for +, x) or the result (for -, /) are stored in a list for the particular
 274  * operation, and each becomes more likely to appear again in that operation.
 275  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 276  * many extra chances of appearing.  Each time it is selected because of this,
 277  * its penalty is decreased by one; it is removed when it reaches 0.
 278  *
 279  * The penalty[] array gives the sum of all penalties in the list for
 280  * each operation and each operand.  The penlist[] array has the lists of
 281  * penalties themselves.
 282  */
 283
 284 int penalty[sizeof(keylist) - 1][2];
 285 struct penalty {
 286         int value, penalty;     /* Penalised value and its penalty. */
 287         struct penalty *next;
 288 } *penlist[sizeof(keylist) - 1][2];
 289
 290 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 291
 292 /*
 293  * Add a penalty for the number `value' to the list for operation `op',
 294  * operand number `operand' (0 or 1).  If we run out of memory, we just
 295  * forget about the penalty (how likely is this, anyway?).
 296  */
 297 penalise(value, op, operand)
 298         int value, op, operand;
 299 {
 300         struct penalty *p;
 301         char *malloc();
 302
 303         op = opnum(op);
 304         if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL)
 305                 return;
 306         p->next = penlist[op][operand];
 307         penlist[op][operand] = p;
 308         penalty[op][operand] += p->penalty = WRONGPENALTY;
 309         p->value = value;
 310 }
 311
 312 /*
 313  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 314  * of operation `op'.  The random number we generate is either used directly
 315  * as a value, or represents a position in the penalty list.  If the latter,
 316  * we find the corresponding value and return that, decreasing its penalty.
 317  */
 318 getrandom(maxval, op, operand)
 319         int maxval, op, operand;
 320 {
 321         int value;
 322         register struct penalty **pp, *p;
 323
 324         op = opnum(op);
 325         value = random() % (maxval + penalty[op][operand]);
 326
 327         /*
 328          * 0 to maxval - 1 is a number to be used directly; bigger values
 329          * are positions to be located in the penalty list.
 330          */
 331         if (value < maxval)
 332                 return(value);
 333         value -= maxval;
 334
 335         /*
 336          * Find the penalty at position `value'; decrement its penalty and
 337          * delete it if it reaches 0; return the corresponding value.
 338          */
 339         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 340                 if (p->penalty > value) {
 341                         value = p->value;
 342                         penalty[op][operand]--;
 343                         if (--(p->penalty) <= 0) {
 344                                 p = p->next;
 345                                 (void)free((char *)*pp);
 346                                 *pp = p;
 347                         }
 348                         return(value);
 349                 }
 350                 value -= p->penalty;
 351         }
 352         /*
 353          * We can only get here if the value from the penalty[] array doesn't
 354          * correspond to the actual sum of penalties in the list.  Provide an
 355          * obscure message.
 356          */
 357         (void)fprintf(stderr, "arithmetic: bug: inconsistent penalties\n");
 358         exit(1);
 359         /* NOTREACHED */
 360 }
 361
 362 /* Return an index for the character op, which is one of [+-x/]. */
 363 opnum(op)
 364         int op;
 365 {
 366         char *p;
 367
 368         if (op == 0 || (p = index(keylist, op)) == NULL) {
 369                 (void)fprintf(stderr,
 370                     "arithmetic: bug: op %c not in keylist %s\n", op, keylist);
 371                 exit(1);
 372         }
 373         return(p - keylist);
 374 }
 375
 376 /* Print usage message and quit. */
 377 usage()
 378 {
 379         (void)fprintf(stderr, "usage: arithmetic [-o +-x/] [-r range]\n");
 380         exit(1);
 381 }