arithmetic/arithmetic.c

   1 /*
   2  * Copyright (c) 1989 The Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Eamonn McManus of Trinity College Dublin.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. All advertising materials mentioning features or use of this software
  17  *    must display the following acknowledgement:
  18  *      This product includes software developed by the University of
  19  *      California, Berkeley and its contributors.
  20  * 4. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  */
  36
  37 #ifndef lint
  38 char copyright[] =
  39 "@(#) Copyright (c) 1989 The Regents of the University of California.\n\
  40  All rights reserved.\n";
  41 #endif /* not lint */
  42
  43 #ifndef lint
  44 static char sccsid[] = "@(#)arithmetic.c        5.5 (Berkeley) 2/27/91";
  45 #endif /* not lint */
  46
  47 /*
  48  * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
  49  *
  50  * The operation of this program mimics that of the standard Unix game
  51  * `arithmetic'.  I've made it as close as I could manage without examining
  52  * the source code.  The principal differences are:
  53  *
  54  * The method of biasing towards numbers that had wrong answers in the past
  55  * is different; original `arithmetic' seems to retain the bias forever,
  56  * whereas this program lets the bias gradually decay as it is used.
  57  *
  58  * Original `arithmetic' delays for some period (3 seconds?) after printing
  59  * the score.  I saw no reason for this delay, so I scrapped it.
  60  *
  61  * There is no longer a limitation on the maximum range that can be supplied
  62  * to the program.  The original program required it to be less than 100.
  63  * Anomalous results may occur with this program if ranges big enough to
  64  * allow overflow are given.
  65  *
  66  * I have obviously not attempted to duplicate bugs in the original.  It
  67  * would go into an infinite loop if invoked as `arithmetic / 0'.  It also
  68  * did not recognise an EOF in its input, and would continue trying to read
  69  * after it.  It did not check that the input was a valid number, treating any
  70  * garbage as 0.  Finally, it did not flush stdout after printing its prompt,
  71  * so in the unlikely event that stdout was not a terminal, it would not work
  72  * properly.
  73  */
  74
  75 #include <sys/types.h>
  76 #include <sys/signal.h>
  77 #include <ctype.h>
  78 #include <stdio.h>
  79 #include <string.h>
  80
  81 char keylist[] = "+-x/";
  82 char defaultkeys[] = "+-";
  83 char *keys = defaultkeys;
  84 int nkeys = sizeof(defaultkeys) - 1;
  85 int rangemax = 10;
  86 int nright, nwrong;
  87 time_t qtime;
  88 #define NQUESTS 20
  89
  90 /*
  91  * Select keys from +-x/ to be asked addition, subtraction, multiplication,
  92  * and division problems.  More than one key may be given.  The default is
  93  * +-.  Specify a range to confine the operands to 0 - range.  Default upper
  94  * bound is 10.  After every NQUESTS questions, statistics on the performance
  95  * so far are printed.
  96  */
  97 void
  98 main(argc, argv)
  99         int argc;
 100         char **argv;
 101 {
 102         extern char *optarg;
 103         extern int optind;
 104         int ch, cnt;
 105         time_t time();
 106         void intr();
 107
 108         while ((ch = getopt(argc, argv, "r:o:")) != EOF)
 109                 switch(ch) {
 110                 case 'o': {
 111                         register char *p;
 112
 113                         for (p = keys = optarg; *p; ++p)
 114                                 if (!index(keylist, *p)) {
 115                                         (void)fprintf(stderr,
 116                                             "arithmetic: unknown key.\n");
 117                                         exit(1);
 118                                 }
 119                         nkeys = p - optarg;
 120                         break;
 121                 }
 122                 case 'r':
 123                         if ((rangemax = atoi(optarg)) <= 0) {
 124                                 (void)fprintf(stderr,
 125                                     "arithmetic: invalid range.\n");
 126                                 exit(1);
 127                         }
 128                         break;
 129                 case '?':
 130                 default:
 131                         usage();
 132                 }
 133         if (argc -= optind)
 134                 usage();
 135
 136         /* Seed the random-number generator. */
 137         srandom((int)time((time_t *)NULL));
 138
 139         (void)signal(SIGINT, intr);
 140
 141         /* Now ask the questions. */
 142         for (;;) {
 143                 for (cnt = NQUESTS; cnt--;)
 144                         if (problem() == EOF)
 145                                 exit(0);
 146                 showstats();
 147         }
 148         /* NOTREACHED */
 149 }
 150
 151 /* Handle interrupt character.  Print score and exit. */
 152 void
 153 intr()
 154 {
 155         showstats();
 156         exit(0);
 157 }
 158
 159 /* Print score.  Original `arithmetic' had a delay after printing it. */
 160 showstats()
 161 {
 162         if (nright + nwrong > 0) {
 163                 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
 164                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 165                 if (nright > 0)
 166         (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 167                             (long)qtime, (float)qtime / nright);
 168         }
 169         (void)printf("\n");
 170 }
 171
 172 /*
 173  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 174  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 175  * selected such that the right operand and either the left operand (for +, x)
 176  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 177  * answer causes the numbers in the problem to be penalised, so that they are
 178  * more likely to appear in subsequent problems.
 179  */
 180 problem()
 181 {
 182         register char *p;
 183         time_t start, finish;
 184         int left, op, right, result;
 185         char line[80];
 186
 187         op = keys[random() % nkeys];
 188         if (op != '/')
 189                 right = getrandom(rangemax + 1, op, 1);
 190 retry:
 191         /* Get the operands. */
 192         switch (op) {
 193         case '+':
 194                 left = getrandom(rangemax + 1, op, 0);
 195                 result = left + right;
 196                 break;
 197         case '-':
 198                 result = getrandom(rangemax + 1, op, 0);
 199                 left = right + result;
 200                 break;
 201         case 'x':
 202                 left = getrandom(rangemax + 1, op, 0);
 203                 result = left * right;
 204                 break;
 205         case '/':
 206                 right = getrandom(rangemax, op, 1) + 1;
 207                 result = getrandom(rangemax + 1, op, 0);
 208                 left = right * result + random() % right;
 209                 break;
 210         }
 211
 212         /*
 213          * A very big maxrange could cause negative values to pop
 214          * up, owing to overflow.
 215          */
 216         if (result < 0 || left < 0)
 217                 goto retry;
 218
 219         (void)printf("%d %c %d =   ", left, op, right);
 220         (void)fflush(stdout);
 221         (void)time(&start);
 222
 223         /*
 224          * Keep looping until the correct answer is given, or until EOF or
 225          * interrupt is typed.
 226          */
 227         for (;;) {
 228                 if (!fgets(line, sizeof(line), stdin)) {
 229                         (void)printf("\n");
 230                         return(EOF);
 231                 }
 232                 for (p = line; *p && isspace(*p); ++p);
 233                 if (!isdigit(*p)) {
 234                         (void)printf("Please type a number.\n");
 235                         continue;
 236                 }
 237                 if (atoi(p) == result) {
 238                         (void)printf("Right!\n");
 239                         ++nright;
 240                         break;
 241                 }
 242                 /* Wrong answer; penalise and ask again. */
 243                 (void)printf("What?\n");
 244                 ++nwrong;
 245                 penalise(right, op, 1);
 246                 if (op == 'x' || op == '+')
 247                         penalise(left, op, 0);
 248                 else
 249                         penalise(result, op, 0);
 250         }
 251
 252         /*
 253          * Accumulate the time taken.  Obviously rounding errors happen here;
 254          * however they should cancel out, because some of the time you are
 255          * charged for a partially elapsed second at the start, and some of
 256          * the time you are not charged for a partially elapsed second at the
 257          * end.
 258          */
 259         (void)time(&finish);
 260         qtime += finish - start;
 261         return(0);
 262 }
 263
 264 /*
 265  * Here is the code for accumulating penalties against the numbers for which
 266  * a wrong answer was given.  The right operand and either the left operand
 267  * (for +, x) or the result (for -, /) are stored in a list for the particular
 268  * operation, and each becomes more likely to appear again in that operation.
 269  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 270  * many extra chances of appearing.  Each time it is selected because of this,
 271  * its penalty is decreased by one; it is removed when it reaches 0.
 272  *
 273  * The penalty[] array gives the sum of all penalties in the list for
 274  * each operation and each operand.  The penlist[] array has the lists of
 275  * penalties themselves.
 276  */
 277
 278 int penalty[sizeof(keylist) - 1][2];
 279 struct penalty {
 280         int value, penalty;     /* Penalised value and its penalty. */
 281         struct penalty *next;
 282 } *penlist[sizeof(keylist) - 1][2];
 283
 284 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 285
 286 /*
 287  * Add a penalty for the number `value' to the list for operation `op',
 288  * operand number `operand' (0 or 1).  If we run out of memory, we just
 289  * forget about the penalty (how likely is this, anyway?).
 290  */
 291 penalise(value, op, operand)
 292         int value, op, operand;
 293 {
 294         struct penalty *p;
 295         char *malloc();
 296
 297         op = opnum(op);
 298         if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL)
 299                 return;
 300         p->next = penlist[op][operand];
 301         penlist[op][operand] = p;
 302         penalty[op][operand] += p->penalty = WRONGPENALTY;
 303         p->value = value;
 304 }
 305
 306 /*
 307  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 308  * of operation `op'.  The random number we generate is either used directly
 309  * as a value, or represents a position in the penalty list.  If the latter,
 310  * we find the corresponding value and return that, decreasing its penalty.
 311  */
 312 getrandom(maxval, op, operand)
 313         int maxval, op, operand;
 314 {
 315         int value;
 316         register struct penalty **pp, *p;
 317
 318         op = opnum(op);
 319         value = random() % (maxval + penalty[op][operand]);
 320
 321         /*
 322          * 0 to maxval - 1 is a number to be used directly; bigger values
 323          * are positions to be located in the penalty list.
 324          */
 325         if (value < maxval)
 326                 return(value);
 327         value -= maxval;
 328
 329         /*
 330          * Find the penalty at position `value'; decrement its penalty and
 331          * delete it if it reaches 0; return the corresponding value.
 332          */
 333         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 334                 if (p->penalty > value) {
 335                         value = p->value;
 336                         penalty[op][operand]--;
 337                         if (--(p->penalty) <= 0) {
 338                                 p = p->next;
 339                                 (void)free((char *)*pp);
 340                                 *pp = p;
 341                         }
 342                         return(value);
 343                 }
 344                 value -= p->penalty;
 345         }
 346         /*
 347          * We can only get here if the value from the penalty[] array doesn't
 348          * correspond to the actual sum of penalties in the list.  Provide an
 349          * obscure message.
 350          */
 351         (void)fprintf(stderr, "arithmetic: bug: inconsistent penalties\n");
 352         exit(1);
 353         /* NOTREACHED */
 354 }
 355
 356 /* Return an index for the character op, which is one of [+-x/]. */
 357 opnum(op)
 358         int op;
 359 {
 360         char *p;
 361
 362         if (op == 0 || (p = index(keylist, op)) == NULL) {
 363                 (void)fprintf(stderr,
 364                     "arithmetic: bug: op %c not in keylist %s\n", op, keylist);
 365                 exit(1);
 366         }
 367         return(p - keylist);
 368 }
 369
 370 /* Print usage message and quit. */
 371 usage()
 372 {
 373         (void)fprintf(stderr, "usage: arithmetic [-o +-x/] [-r range]\n");
 374         exit(1);
 375 }