arithmetic/arithmetic.c

   1 /*      $NetBSD: arithmetic.c,v 1.8 1997/10/10 11:49:44 lukem 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 1.8 1997/10/10 11:49:44 lukem 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
  90 int     getrandom __P((int, int, int));
  91 void    intr __P((int));
  92 int     main __P((int, char *[]));
  93 int     opnum __P((int));
  94 void    penalise __P((int, int, int));
  95 int     problem __P((void));
  96 void    showstats __P((void));
  97 void    usage __P((void));
  98
  99 char keylist[] = "+-x/";
 100 char defaultkeys[] = "+-";
 101 char *keys = defaultkeys;
 102 int nkeys = sizeof(defaultkeys) - 1;
 103 int rangemax = 10;
 104 int nright, nwrong;
 105 time_t qtime;
 106 #define NQUESTS 20
 107
 108 /*
 109  * Select keys from +-x/ to be asked addition, subtraction, multiplication,
 110  * and division problems.  More than one key may be given.  The default is
 111  * +-.  Specify a range to confine the operands to 0 - range.  Default upper
 112  * bound is 10.  After every NQUESTS questions, statistics on the performance
 113  * so far are printed.
 114  */
 115 int
 116 main(argc, argv)
 117         int argc;
 118         char **argv;
 119 {
 120         extern char *optarg;
 121         extern int optind;
 122         int ch, cnt;
 123
 124         while ((ch = getopt(argc, argv, "r:o:")) != -1)
 125                 switch(ch) {
 126                 case 'o': {
 127                         char *p;
 128
 129                         for (p = keys = optarg; *p; ++p)
 130                                 if (!strchr(keylist, *p))
 131                                         errx(1, "arithmetic: unknown key.");
 132                         nkeys = p - optarg;
 133                         break;
 134                 }
 135                 case 'r':
 136                         if ((rangemax = atoi(optarg)) <= 0)
 137                                 errx(1, "arithmetic: invalid range.");
 138                         break;
 139                 case '?':
 140                 default:
 141                         usage();
 142                 }
 143         if (argc -= optind)
 144                 usage();
 145
 146         /* Seed the random-number generator. */
 147         srandom((int)time((time_t *)NULL));
 148
 149         (void)signal(SIGINT, intr);
 150
 151         /* Now ask the questions. */
 152         for (;;) {
 153                 for (cnt = NQUESTS; cnt--;)
 154                         if (problem() == EOF)
 155                                 exit(0);
 156                 showstats();
 157         }
 158         /* NOTREACHED */
 159 }
 160
 161 /* Handle interrupt character.  Print score and exit. */
 162 void
 163 intr(dummy)
 164         int dummy;
 165 {
 166         showstats();
 167         exit(0);
 168 }
 169
 170 /* Print score.  Original `arithmetic' had a delay after printing it. */
 171 void
 172 showstats()
 173 {
 174         if (nright + nwrong > 0) {
 175                 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
 176                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 177                 if (nright > 0)
 178         (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 179                             (long)qtime, (float)qtime / nright);
 180         }
 181         (void)printf("\n");
 182 }
 183
 184 /*
 185  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 186  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 187  * selected such that the right operand and either the left operand (for +, x)
 188  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 189  * answer causes the numbers in the problem to be penalised, so that they are
 190  * more likely to appear in subsequent problems.
 191  */
 192 int
 193 problem()
 194 {
 195         char *p;
 196         time_t start, finish;
 197         int left, op, right, result;
 198         char line[80];
 199
 200         left = result = 0;
 201         op = keys[random() % nkeys];
 202         if (op != '/')
 203                 right = getrandom(rangemax + 1, op, 1);
 204 retry:
 205         /* Get the operands. */
 206         switch (op) {
 207         case '+':
 208                 left = getrandom(rangemax + 1, op, 0);
 209                 result = left + right;
 210                 break;
 211         case '-':
 212                 result = getrandom(rangemax + 1, op, 0);
 213                 left = right + result;
 214                 break;
 215         case 'x':
 216                 left = getrandom(rangemax + 1, op, 0);
 217                 result = left * right;
 218                 break;
 219         case '/':
 220                 right = getrandom(rangemax, op, 1) + 1;
 221                 result = getrandom(rangemax + 1, op, 0);
 222                 left = right * result + random() % right;
 223                 break;
 224         }
 225
 226         /*
 227          * A very big maxrange could cause negative values to pop
 228          * up, owing to overflow.
 229          */
 230         if (result < 0 || left < 0)
 231                 goto retry;
 232
 233         (void)printf("%d %c %d =   ", left, op, right);
 234         (void)fflush(stdout);
 235         (void)time(&start);
 236
 237         /*
 238          * Keep looping until the correct answer is given, or until EOF or
 239          * interrupt is typed.
 240          */
 241         for (;;) {
 242                 if (!fgets(line, sizeof(line), stdin)) {
 243                         (void)printf("\n");
 244                         return(EOF);
 245                 }
 246                 for (p = line; *p && isspace(*p); ++p);
 247                 if (!isdigit(*p)) {
 248                         (void)printf("Please type a number.\n");
 249                         continue;
 250                 }
 251                 if (atoi(p) == result) {
 252                         (void)printf("Right!\n");
 253                         ++nright;
 254                         break;
 255                 }
 256                 /* Wrong answer; penalise and ask again. */
 257                 (void)printf("What?\n");
 258                 ++nwrong;
 259                 penalise(right, op, 1);
 260                 if (op == 'x' || op == '+')
 261                         penalise(left, op, 0);
 262                 else
 263                         penalise(result, op, 0);
 264         }
 265
 266         /*
 267          * Accumulate the time taken.  Obviously rounding errors happen here;
 268          * however they should cancel out, because some of the time you are
 269          * charged for a partially elapsed second at the start, and some of
 270          * the time you are not charged for a partially elapsed second at the
 271          * end.
 272          */
 273         (void)time(&finish);
 274         qtime += finish - start;
 275         return(0);
 276 }
 277
 278 /*
 279  * Here is the code for accumulating penalties against the numbers for which
 280  * a wrong answer was given.  The right operand and either the left operand
 281  * (for +, x) or the result (for -, /) are stored in a list for the particular
 282  * operation, and each becomes more likely to appear again in that operation.
 283  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 284  * many extra chances of appearing.  Each time it is selected because of this,
 285  * its penalty is decreased by one; it is removed when it reaches 0.
 286  *
 287  * The penalty[] array gives the sum of all penalties in the list for
 288  * each operation and each operand.  The penlist[] array has the lists of
 289  * penalties themselves.
 290  */
 291
 292 int penalty[sizeof(keylist) - 1][2];
 293 struct penalty {
 294         int value, penalty;     /* Penalised value and its penalty. */
 295         struct penalty *next;
 296 } *penlist[sizeof(keylist) - 1][2];
 297
 298 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 299
 300 /*
 301  * Add a penalty for the number `value' to the list for operation `op',
 302  * operand number `operand' (0 or 1).  If we run out of memory, we just
 303  * forget about the penalty (how likely is this, anyway?).
 304  */
 305 void
 306 penalise(value, op, operand)
 307         int value, op, operand;
 308 {
 309         struct penalty *p;
 310
 311         op = opnum(op);
 312         if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL)
 313                 return;
 314         p->next = penlist[op][operand];
 315         penlist[op][operand] = p;
 316         penalty[op][operand] += p->penalty = WRONGPENALTY;
 317         p->value = value;
 318 }
 319
 320 /*
 321  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 322  * of operation `op'.  The random number we generate is either used directly
 323  * as a value, or represents a position in the penalty list.  If the latter,
 324  * we find the corresponding value and return that, decreasing its penalty.
 325  */
 326 int
 327 getrandom(maxval, op, operand)
 328         int maxval, op, operand;
 329 {
 330         int value;
 331         struct penalty **pp, *p;
 332
 333         op = opnum(op);
 334         value = random() % (maxval + penalty[op][operand]);
 335
 336         /*
 337          * 0 to maxval - 1 is a number to be used directly; bigger values
 338          * are positions to be located in the penalty list.
 339          */
 340         if (value < maxval)
 341                 return(value);
 342         value -= maxval;
 343
 344         /*
 345          * Find the penalty at position `value'; decrement its penalty and
 346          * delete it if it reaches 0; return the corresponding value.
 347          */
 348         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 349                 if (p->penalty > value) {
 350                         value = p->value;
 351                         penalty[op][operand]--;
 352                         if (--(p->penalty) <= 0) {
 353                                 p = p->next;
 354                                 (void)free((char *)*pp);
 355                                 *pp = p;
 356                         }
 357                         return(value);
 358                 }
 359                 value -= p->penalty;
 360         }
 361         /*
 362          * We can only get here if the value from the penalty[] array doesn't
 363          * correspond to the actual sum of penalties in the list.  Provide an
 364          * obscure message.
 365          */
 366         errx(1, "arithmetic: bug: inconsistent penalties.");
 367         /* NOTREACHED */
 368 }
 369
 370 /* Return an index for the character op, which is one of [+-x/]. */
 371 int
 372 opnum(op)
 373         int op;
 374 {
 375         char *p;
 376
 377         if (op == 0 || (p = strchr(keylist, op)) == NULL)
 378                 errx(1, "arithmetic: bug: op %c not in keylist %s",
 379                     op, keylist);
 380         return(p - keylist);
 381 }
 382
 383 /* Print usage message and quit. */
 384 void
 385 usage()
 386 {
 387         extern char *__progname;        /* from crt0.o */
 388
 389         (void)fprintf(stderr, "usage: %s [-o +-x/] [-r range]\n",
 390                 __progname);
 391         exit(1);
 392 }