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. 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  * @(#) Copyright (c) 1989, 1993 The Regents of the University of California.  All rights reserved.
  37  * @(#)arithmetic.c     8.1 (Berkeley) 5/31/93
  38  * $FreeBSD: src/games/arithmetic/arithmetic.c,v 1.10 1999/12/12 06:40:28 billf Exp $
  39  * $DragonFly: src/games/arithmetic/arithmetic.c,v 1.4 2005/04/24 15:31:30 liamfoy Exp $
  40  */
  41
  42 /*
  43  * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
  44  *
  45  * The operation of this program mimics that of the standard Unix game
  46  * `arithmetic'.  I've made it as close as I could manage without examining
  47  * the source code.  The principal differences are:
  48  *
  49  * The method of biasing towards numbers that had wrong answers in the past
  50  * is different; original `arithmetic' seems to retain the bias forever,
  51  * whereas this program lets the bias gradually decay as it is used.
  52  *
  53  * Original `arithmetic' delays for some period (3 seconds?) after printing
  54  * the score.  I saw no reason for this delay, so I scrapped it.
  55  *
  56  * There is no longer a limitation on the maximum range that can be supplied
  57  * to the program.  The original program required it to be less than 100.
  58  * Anomalous results may occur with this program if ranges big enough to
  59  * allow overflow are given.
  60  *
  61  * I have obviously not attempted to duplicate bugs in the original.  It
  62  * would go into an infinite loop if invoked as `arithmetic / 0'.  It also
  63  * did not recognise an EOF in its input, and would continue trying to read
  64  * after it.  It did not check that the input was a valid number, treating any
  65  * garbage as 0.  Finally, it did not flush stdout after printing its prompt,
  66  * so in the unlikely event that stdout was not a terminal, it would not work
  67  * properly.
  68  */
  69
  70 #include <sys/types.h>
  71 #include <sys/signal.h>
  72 #include <ctype.h>
  73 #include <stdio.h>
  74 #include <string.h>
  75 #include <stdlib.h>
  76 #include <time.h>
  77 #include <unistd.h>
  78
  79 const char keylist[] = "+-x/";
  80 const char defaultkeys[] = "+-";
  81 const char *keys = defaultkeys;
  82 int nkeys = sizeof(defaultkeys) - 1;
  83 int rangemax = 10;
  84 int nright, nwrong;
  85 time_t qtime;
  86 #define NQUESTS 20
  87
  88 static void usage (void);
  89 int getrandom (int, int, int);
  90 void intr (int);
  91 int opnum (int);
  92 void penalise (int, int, int);
  93 int problem (void);
  94 void showstats (void);
  95
  96 /*
  97  * Select keys from +-x/ to be asked addition, subtraction, multiplication,
  98  * and division problems.  More than one key may be given.  The default is
  99  * +-.  Specify a range to confine the operands to 0 - range.  Default upper
 100  * bound is 10.  After every NQUESTS questions, statistics on the performance
 101  * so far are printed.
 102  */
 103 int
 104 main(int argc, char **argv)
 105 {
 106         int ch, cnt;
 107
 108         /* Revoke setgid privileges */
 109         setgid(getgid());
 110
 111         while ((ch = getopt(argc, argv, "r:o:")) != -1)
 112                 switch(ch) {
 113                 case 'o': {
 114                         const char *p;
 115
 116                         for (p = keys = optarg; *p; ++p)
 117                                 if (!index(keylist, *p)) {
 118                                         (void)fprintf(stderr,
 119                                             "arithmetic: unknown key.\n");
 120                                         exit(1);
 121                                 }
 122                         nkeys = p - optarg;
 123                         break;
 124                 }
 125                 case 'r':
 126                         if ((rangemax = atoi(optarg)) <= 0) {
 127                                 (void)fprintf(stderr,
 128                                     "arithmetic: invalid range.\n");
 129                                 exit(1);
 130                         }
 131                         break;
 132                 case '?':
 133                 default:
 134                         usage();
 135                 }
 136         if (argc -= optind)
 137                 usage();
 138
 139         /* Seed the random-number generator. */
 140         srandomdev();
 141
 142         (void)signal(SIGINT, intr);
 143
 144         /* Now ask the questions. */
 145         for (;;) {
 146                 for (cnt = NQUESTS; cnt--;)
 147                         if (problem() == EOF)
 148                                 exit(0);
 149                 showstats();
 150         }
 151         /* NOTREACHED */
 152 }
 153
 154 /* Handle interrupt character.  Print score and exit. */
 155 void
 156 intr(__unused int sig)
 157 {
 158         showstats();
 159         exit(0);
 160 }
 161
 162 /* Print score.  Original `arithmetic' had a delay after printing it. */
 163 void
 164 showstats(void)
 165 {
 166         if (nright + nwrong > 0) {
 167                 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
 168                     nright, nwrong, (int)(100L * nright / (nright + nwrong)));
 169                 if (nright > 0)
 170         (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
 171                             (long)qtime, (float)qtime / nright);
 172         }
 173         (void)printf("\n");
 174 }
 175
 176 /*
 177  * Pick a problem and ask it.  Keeps asking the same problem until supplied
 178  * with the correct answer, or until EOF or interrupt is typed.  Problems are
 179  * selected such that the right operand and either the left operand (for +, x)
 180  * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 181  * answer causes the numbers in the problem to be penalised, so that they are
 182  * more likely to appear in subsequent problems.
 183  */
 184 int
 185 problem(void)
 186 {
 187         char *p;
 188         time_t start, finish;
 189         int left, op, right, result;
 190         char line[80];
 191
 192         left = 0;
 193         right = 0;
 194         result = 0;
 195         op = keys[random() % nkeys];
 196         if (op != '/')
 197                 right = getrandom(rangemax + 1, op, 1);
 198 retry:
 199         /* Get the operands. */
 200         switch (op) {
 201         case '+':
 202                 left = getrandom(rangemax + 1, op, 0);
 203                 result = left + right;
 204                 break;
 205         case '-':
 206                 result = getrandom(rangemax + 1, op, 0);
 207                 left = right + result;
 208                 break;
 209         case 'x':
 210                 left = getrandom(rangemax + 1, op, 0);
 211                 result = left * right;
 212                 break;
 213         case '/':
 214                 right = getrandom(rangemax, op, 1) + 1;
 215                 result = getrandom(rangemax + 1, op, 0);
 216                 left = right * result + random() % right;
 217                 break;
 218         }
 219
 220         /*
 221          * A very big maxrange could cause negative values to pop
 222          * up, owing to overflow.
 223          */
 224         if (result < 0 || left < 0)
 225                 goto retry;
 226
 227         (void)printf("%d %c %d =   ", left, op, right);
 228         (void)fflush(stdout);
 229         (void)time(&start);
 230
 231         /*
 232          * Keep looping until the correct answer is given, or until EOF or
 233          * interrupt is typed.
 234          */
 235         for (;;) {
 236                 if (!fgets(line, sizeof(line), stdin)) {
 237                         (void)printf("\n");
 238                         return(EOF);
 239                 }
 240                 for (p = line; *p && isspace(*p); ++p);
 241                 if (!isdigit(*p)) {
 242                         (void)printf("Please type a number.\n");
 243                         continue;
 244                 }
 245                 if (atoi(p) == result) {
 246                         (void)printf("Right!\n");
 247                         ++nright;
 248                         break;
 249                 }
 250                 /* Wrong answer; penalise and ask again. */
 251                 (void)printf("What?\n");
 252                 ++nwrong;
 253                 penalise(right, op, 1);
 254                 if (op == 'x' || op == '+')
 255                         penalise(left, op, 0);
 256                 else
 257                         penalise(result, op, 0);
 258         }
 259
 260         /*
 261          * Accumulate the time taken.  Obviously rounding errors happen here;
 262          * however they should cancel out, because some of the time you are
 263          * charged for a partially elapsed second at the start, and some of
 264          * the time you are not charged for a partially elapsed second at the
 265          * end.
 266          */
 267         (void)time(&finish);
 268         qtime += finish - start;
 269         return(0);
 270 }
 271
 272 /*
 273  * Here is the code for accumulating penalties against the numbers for which
 274  * a wrong answer was given.  The right operand and either the left operand
 275  * (for +, x) or the result (for -, /) are stored in a list for the particular
 276  * operation, and each becomes more likely to appear again in that operation.
 277  * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 278  * many extra chances of appearing.  Each time it is selected because of this,
 279  * its penalty is decreased by one; it is removed when it reaches 0.
 280  *
 281  * The penalty[] array gives the sum of all penalties in the list for
 282  * each operation and each operand.  The penlist[] array has the lists of
 283  * penalties themselves.
 284  */
 285
 286 int penalty[sizeof(keylist) - 1][2];
 287 struct penalty {
 288         int value, penalty;     /* Penalised value and its penalty. */
 289         struct penalty *next;
 290 } *penlist[sizeof(keylist) - 1][2];
 291
 292 #define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */
 293
 294 /*
 295  * Add a penalty for the number `value' to the list for operation `op',
 296  * operand number `operand' (0 or 1).  If we run out of memory, we just
 297  * forget about the penalty (how likely is this, anyway?).
 298  */
 299 void
 300 penalise(int value, int op, int operand)
 301 {
 302         struct penalty *p;
 303
 304         op = opnum(op);
 305         if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL)
 306                 return;
 307         p->next = penlist[op][operand];
 308         penlist[op][operand] = p;
 309         penalty[op][operand] += p->penalty = WRONGPENALTY;
 310         p->value = value;
 311 }
 312
 313 /*
 314  * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 315  * of operation `op'.  The random number we generate is either used directly
 316  * as a value, or represents a position in the penalty list.  If the latter,
 317  * we find the corresponding value and return that, decreasing its penalty.
 318  */
 319 int
 320 getrandom(int maxval, int op, int operand)
 321 {
 322         int value;
 323         struct penalty **pp, *p;
 324
 325         op = opnum(op);
 326         value = random() % (maxval + penalty[op][operand]);
 327
 328         /*
 329          * 0 to maxval - 1 is a number to be used directly; bigger values
 330          * are positions to be located in the penalty list.
 331          */
 332         if (value < maxval)
 333                 return(value);
 334         value -= maxval;
 335
 336         /*
 337          * Find the penalty at position `value'; decrement its penalty and
 338          * delete it if it reaches 0; return the corresponding value.
 339          */
 340         for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
 341                 if (p->penalty > value) {
 342                         value = p->value;
 343                         penalty[op][operand]--;
 344                         if (--(p->penalty) <= 0) {
 345                                 p = p->next;
 346                                 (void)free((char *)*pp);
 347                                 *pp = p;
 348                         }
 349                         return(value);
 350                 }
 351                 value -= p->penalty;
 352         }
 353         /*
 354          * We can only get here if the value from the penalty[] array doesn't
 355          * correspond to the actual sum of penalties in the list.  Provide an
 356          * obscure message.
 357          */
 358         (void)fprintf(stderr, "arithmetic: bug: inconsistent penalties\n");
 359         exit(1);
 360         /* NOTREACHED */
 361 }
 362
 363 /* Return an index for the character op, which is one of [+-x/]. */
 364 int
 365 opnum(int op)
 366 {
 367         char *p;
 368
 369         if (op == 0 || (p = index(keylist, op)) == NULL) {
 370                 (void)fprintf(stderr,
 371                     "arithmetic: bug: op %c not in keylist %s\n", op, keylist);
 372                 exit(1);
 373         }
 374         return(p - keylist);
 375 }
 376
 377 /* Print usage message and quit. */
 378 static void
 379 usage(void)
 380 {
 381         (void)fprintf(stderr, "usage: arithmetic [-o +-x/] [-r range]\n");
 382         exit(1);
 383 }