games/arithmetic/arithmetic.c

   1 /*-
   2  * Copyright (c) 1989, 1993
   3  *      The Regents of the University of California.  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. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  33  * @(#)arithmetic.c     8.1 (Berkeley) 5/31/93
  34  * $FreeBSD: src/games/arithmetic/arithmetic.c,v 1.10 1999/12/12 06:40:28 billf Exp $
  35  */
  36
  37 /*
  38  * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
  39  *
  40  * The operation of this program mimics that of the standard Unix game
  41  * `arithmetic'.  I've made it as close as I could manage without examining
  42  * the source code.  The principal differences are:
  43  *
  44  * The method of biasing towards numbers that had wrong answers in the past
  45  * is different; original `arithmetic' seems to retain the bias forever,
  46  * whereas this program lets the bias gradually decay as it is used.
  47  *
  48  * Original `arithmetic' delays for some period (3 seconds?) after printing
  49  * the score.  I saw no reason for this delay, so I scrapped it.
  50  *
  51  * There is no longer a limitation on the maximum range that can be supplied
  52  * to the program.  The original program required it to be less than 100.
  53  * Anomalous results may occur with this program if ranges big enough to
  54  * allow overflow are given.
  55  *
  56  * I have obviously not attempted to duplicate bugs in the original.  It
  57  * would go into an infinite loop if invoked as `arithmetic / 0'.  It also
  58  * did not recognise an EOF in its input, and would continue trying to read
  59  * after it.  It did not check that the input was a valid number, treating any
  60  * garbage as 0.  Finally, it did not flush stdout after printing its prompt,
  61  * so in the unlikely event that stdout was not a terminal, it would not work
  62  * properly.
  63  */
  64
  65 #include <sys/types.h>
  66 #include <ctype.h>
  67 #include <signal.h>
  68 #include <stdio.h>
  69 #include <stdlib.h>
  70 #include <string.h>
  71 #include <time.h>
  72 #include <unistd.h>
  73
  74 int getrandom(int, int, int);
  75 void intr(int);
  76 int opnum(int);
  77 void penalise(int, int, int);
  78 int problem(void);
  79 void showstats(void);
  80 static void usage(void);
  81
  82 const char keylist[] = "+-x/";
  83 const char defaultkeys[] = "+-";
  84 const char *keys = defaultkeys;
  85 int nkeys = sizeof(defaultkeys) - 1;
  86 int rangemax = 10;
  87 int nright, nwrong;
  88 time_t qtime;
  89 #define NQUESTS 20
  90
  91 /*
  92  * Select keys from +-x/ to be asked addition, subtraction, multiplication,
  93  * and division problems.  More than one key may be given.  The default is
  94  * +-.  Specify a range to confine the operands to 0 - range.  Default upper
  95  * bound is 10.  After every NQUESTS questions, statistics on the performance
  96  * so far are printed.
  97  */
  98 int
  99 main(int argc, char *argv[])
 100 {
 101         int ch, cnt;
 102
 103         /* Revoke setgid privileges */
 104         setgid(getgid());
 105
 106         while ((ch = getopt(argc, argv, "r:o:")) != -1)
 107                 switch(ch) {
 108                 case 'o': {
 109                         const char *p;
 110
 111                         for (p = keys = optarg; *p; ++p)
 112                                 if (!index(keylist, *p)) {
 113                                         fprintf(stderr,
 114                                             "arithmetic: unknown key.\n");
 115                                         exit(1);
 116                                 }
 117                         nkeys = p - optarg;
 118                         break;
 119                 }
 120                 case 'r':
 121                         if ((rangemax = atoi(optarg)) <= 0) {
 122                                 fprintf(stderr,
 123                                     "arithmetic: invalid range.\n");
 124                                 exit(1);
 125                         }
 126                         break;
 127                 case '?':
 128                 default:
 129                         usage();
 130                 }
 131         if (argc -= optind)
 132                 usage();
 133
 134         /* Seed the random-number generator. */
 135         srandomdev();
 136
 137         signal(SIGINT, intr);
 138
 139         /* Now ask the questions. */
 140         for (;;) {
 141                 for (cnt = NQUESTS; cnt--;)
 142                         if (problem() == EOF)
 143                                 exit(0);
 144                 showstats();
 145         }
 146         /* NOTREACHED */
 147 }
 148
 149 /* Handle interrupt character.  Print score and exit. */
 150 void
 151 intr(__unused int sig)
 152 {
 153         showstats();
 154         exit(0);
 155 }
 156
 157 /* Print score.  Original `arithmetic' had a delay after printing it. */
 158 void
 159 showstats(void)
 160 {
 161         if (nright + nwrong > 0) {
 162                 printf("\n\nRights %d; Wrongs %d; Score %d%%",
 163                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 164                 if (nright > 0)
 165         printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 166                             (long)qtime, (float)qtime / nright);
 167         }
 168         printf("\n");
 169 }
 170
 171 /*
 172  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 173  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 174  * selected such that the right operand and either the left operand (for +, x)
 175  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 176  * answer causes the numbers in the problem to be penalised, so that they are
 177  * more likely to appear in subsequent problems.
 178  */
 179 int
 180 problem(void)
 181 {
 182         char *p;
 183         time_t start, finish;
 184         int left, op, right, result;
 185         char line[80];
 186
 187         left = 0;
 188         right = 0;
 189         result = 0;
 190         op = keys[random() % nkeys];
 191         if (op != '/')
 192                 right = getrandom(rangemax + 1, op, 1);
 193 retry:
 194         /* Get the operands. */
 195         switch (op) {
 196         case '+':
 197                 left = getrandom(rangemax + 1, op, 0);
 198                 result = left + right;
 199                 break;
 200         case '-':
 201                 result = getrandom(rangemax + 1, op, 0);
 202                 left = right + result;
 203                 break;
 204         case 'x':
 205                 left = getrandom(rangemax + 1, op, 0);
 206                 result = left * right;
 207                 break;
 208         case '/':
 209                 right = getrandom(rangemax, op, 1) + 1;
 210                 result = getrandom(rangemax + 1, op, 0);
 211                 left = right * result + random() % right;
 212                 break;
 213         }
 214
 215         /*
 216          * A very big maxrange could cause negative values to pop
 217          * up, owing to overflow.
 218          */
 219         if (result < 0 || left < 0)
 220                 goto retry;
 221
 222         printf("%d %c %d =   ", left, op, right);
 223         fflush(stdout);
 224         time(&start);
 225
 226         /*
 227          * Keep looping until the correct answer is given, or until EOF or
 228          * interrupt is typed.
 229          */
 230         for (;;) {
 231                 if (!fgets(line, sizeof(line), stdin)) {
 232                         printf("\n");
 233                         return(EOF);
 234                 }
 235                 for (p = line; *p && isspace(*p); ++p);
 236                 if (!isdigit(*p)) {
 237                         printf("Please type a number.\n");
 238                         continue;
 239                 }
 240                 if (atoi(p) == result) {
 241                         printf("Right!\n");
 242                         ++nright;
 243                         break;
 244                 }
 245                 /* Wrong answer; penalise and ask again. */
 246                 printf("What?\n");
 247                 ++nwrong;
 248                 penalise(right, op, 1);
 249                 if (op == 'x' || op == '+')
 250                         penalise(left, op, 0);
 251                 else
 252                         penalise(result, op, 0);
 253         }
 254
 255         /*
 256          * Accumulate the time taken.  Obviously rounding errors happen here;
 257          * however they should cancel out, because some of the time you are
 258          * charged for a partially elapsed second at the start, and some of
 259          * the time you are not charged for a partially elapsed second at the
 260          * end.
 261          */
 262         time(&finish);
 263         qtime += finish - start;
 264         return(0);
 265 }
 266
 267 /*
 268  * Here is the code for accumulating penalties against the numbers for which
 269  * a wrong answer was given.  The right operand and either the left operand
 270  * (for +, x) or the result (for -, /) are stored in a list for the particular
 271  * operation, and each becomes more likely to appear again in that operation.
 272  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 273  * many extra chances of appearing.  Each time it is selected because of this,
 274  * its penalty is decreased by one; it is removed when it reaches 0.
 275  *
 276  * The penalty[] array gives the sum of all penalties in the list for
 277  * each operation and each operand.  The penlist[] array has the lists of
 278  * penalties themselves.
 279  */
 280
 281 int penalty[sizeof(keylist) - 1][2];
 282 struct penalty {
 283         int value, penalty;     /* Penalised value and its penalty. */
 284         struct penalty *next;
 285 } *penlist[sizeof(keylist) - 1][2];
 286
 287 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 288
 289 /*
 290  * Add a penalty for the number `value' to the list for operation `op',
 291  * operand number `operand' (0 or 1).  If we run out of memory, we just
 292  * forget about the penalty (how likely is this, anyway?).
 293  */
 294 void
 295 penalise(int value, int op, int operand)
 296 {
 297         struct penalty *p;
 298
 299         op = opnum(op);
 300         if ((p = malloc(sizeof(*p))) == NULL)
 301                 return;
 302         p->next = penlist[op][operand];
 303         penlist[op][operand] = p;
 304         penalty[op][operand] += p->penalty = WRONGPENALTY;
 305         p->value = value;
 306 }
 307
 308 /*
 309  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 310  * of operation `op'.  The random number we generate is either used directly
 311  * as a value, or represents a position in the penalty list.  If the latter,
 312  * we find the corresponding value and return that, decreasing its penalty.
 313  */
 314 int
 315 getrandom(int maxval, int op, int operand)
 316 {
 317         int value;
 318         struct penalty **pp, *p;
 319
 320         op = opnum(op);
 321         value = random() % (maxval + penalty[op][operand]);
 322
 323         /*
 324          * 0 to maxval - 1 is a number to be used directly; bigger values
 325          * are positions to be located in the penalty list.
 326          */
 327         if (value < maxval)
 328                 return(value);
 329         value -= maxval;
 330
 331         /*
 332          * Find the penalty at position `value'; decrement its penalty and
 333          * delete it if it reaches 0; return the corresponding value.
 334          */
 335         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 336                 if (p->penalty > value) {
 337                         value = p->value;
 338                         penalty[op][operand]--;
 339                         if (--(p->penalty) <= 0) {
 340                                 p = p->next;
 341                                 free((char *)*pp);
 342                                 *pp = p;
 343                         }
 344                         return(value);
 345                 }
 346                 value -= p->penalty;
 347         }
 348         /*
 349          * We can only get here if the value from the penalty[] array doesn't
 350          * correspond to the actual sum of penalties in the list.  Provide an
 351          * obscure message.
 352          */
 353         fprintf(stderr, "arithmetic: bug: inconsistent penalties\n");
 354         exit(1);
 355         /* NOTREACHED */
 356 }
 357
 358 /* Return an index for the character op, which is one of [+-x/]. */
 359 int
 360 opnum(int op)
 361 {
 362         char *p;
 363
 364         if (op == 0 || (p = index(keylist, op)) == NULL) {
 365                 fprintf(stderr,
 366                     "arithmetic: bug: op %c not in keylist %s\n", op, keylist);
 367                 exit(1);
 368         }
 369         return(p - keylist);
 370 }
 371
 372 /* Print usage message and quit. */
 373 static void
 374 usage(void)
 375 {
 376         fprintf(stderr, "usage: arithmetic [-o +-x/] [-r range]\n");
 377         exit(1);
 378 }