usr/src/games/arithmetic/arithmetic.c

/*
 * Copyright (c) 1989 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Eamonn McManus of Trinity College Dublin.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef lint
char copyright[] =
"@(#) Copyright (c) 1989 The Regents of the University of California.\n\
 All rights reserved.\n";
#endif /* not lint */

#ifndef lint
static char sccsid[] = "@(#)arithmetic.c        5.5 (Berkeley) 2/27/91";
#endif /* not lint */

/*
 * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
 *
 * The operation of this program mimics that of the standard Unix game
 * `arithmetic'.  I've made it as close as I could manage without examining
 * the source code.  The principal differences are:
 *
 * The method of biasing towards numbers that had wrong answers in the past
 * is different; original `arithmetic' seems to retain the bias forever,
 * whereas this program lets the bias gradually decay as it is used.
 *
 * Original `arithmetic' delays for some period (3 seconds?) after printing
 * the score.  I saw no reason for this delay, so I scrapped it.
 *
 * There is no longer a limitation on the maximum range that can be supplied
 * to the program.  The original program required it to be less than 100.
 * Anomalous results may occur with this program if ranges big enough to
 * allow overflow are given.
 *
 * I have obviously not attempted to duplicate bugs in the original.  It
 * would go into an infinite loop if invoked as `arithmetic / 0'.  It also
 * did not recognise an EOF in its input, and would continue trying to read
 * after it.  It did not check that the input was a valid number, treating any
 * garbage as 0.  Finally, it did not flush stdout after printing its prompt,
 * so in the unlikely event that stdout was not a terminal, it would not work
 * properly.
 */

#include <sys/types.h>
#include <sys/signal.h>
#include <ctype.h>
#include <stdio.h>
#include <string.h>

char keylist[] = "+-x/";
char defaultkeys[] = "+-";
char *keys = defaultkeys;
int nkeys = sizeof(defaultkeys) - 1;
int rangemax = 10;
int nright, nwrong;
time_t qtime;
#define NQUESTS 20

/*
 * Select keys from +-x/ to be asked addition, subtraction, multiplication,
 * and division problems.  More than one key may be given.  The default is
 * +-.  Specify a range to confine the operands to 0 - range.  Default upper
 * bound is 10.  After every NQUESTS questions, statistics on the performance
 * so far are printed.
 */
void
main(argc, argv)
        int argc;
        char **argv;
{
        extern char *optarg;
        extern int optind;
        int ch, cnt;
        time_t time();
        void intr();

        while ((ch = getopt(argc, argv, "r:o:")) != EOF)
                switch(ch) {
                case 'o': {
                        register char *p;

                        for (p = keys = optarg; *p; ++p)
                                if (!index(keylist, *p)) {
                                        (void)fprintf(stderr,
                                            "arithmetic: unknown key.\n");
                                        exit(1);
                                }
                        nkeys = p - optarg;
                        break;
                }
                case 'r':
                        if ((rangemax = atoi(optarg)) <= 0) {
                                (void)fprintf(stderr,
                                    "arithmetic: invalid range.\n");
                                exit(1);
                        }
                        break;
                case '?':
                default:
                        usage();
                }
        if (argc -= optind)
                usage();

        /* Seed the random-number generator. */
        srandom((int)time((time_t *)NULL));

        (void)signal(SIGINT, intr);

        /* Now ask the questions. */
        for (;;) {
                for (cnt = NQUESTS; cnt--;)
                        if (problem() == EOF)
                                exit(0);
                showstats();
        }
        /* NOTREACHED */
}

/* Handle interrupt character.  Print score and exit. */
void
intr()
{
        showstats();
        exit(0);
}

/* Print score.  Original `arithmetic' had a delay after printing it. */
showstats()
{
        if (nright + nwrong > 0) {
                (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
                    nright, nwrong, (int)(100L * nright / (nright + nwrong)));
                if (nright > 0)
        (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
                            (long)qtime, (float)qtime / nright);
        }
        (void)printf("\n");
}

/*
 * Pick a problem and ask it.  Keeps asking the same problem until supplied
 * with the correct answer, or until EOF or interrupt is typed.  Problems are
 * selected such that the right operand and either the left operand (for +, x)
 * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
 * answer causes the numbers in the problem to be penalised, so that they are
 * more likely to appear in subsequent problems.
 */
problem()
{
        register char *p;
        time_t start, finish;
        int left, op, right, result;
        char line[80];

        op = keys[random() % nkeys];
        if (op != '/')
                right = getrandom(rangemax + 1, op, 1);
retry:
        /* Get the operands. */
        switch (op) {
        case '+':
                left = getrandom(rangemax + 1, op, 0);
                result = left + right;
                break;
        case '-':
                result = getrandom(rangemax + 1, op, 0);
                left = right + result;
                break;
        case 'x':
                left = getrandom(rangemax + 1, op, 0);
                result = left * right;
                break;
        case '/':
                right = getrandom(rangemax, op, 1) + 1;
                result = getrandom(rangemax + 1, op, 0);
                left = right * result + random() % right;
                break;
        }

        /*
         * A very big maxrange could cause negative values to pop
         * up, owing to overflow.
         */
        if (result < 0 || left < 0)
                goto retry;

        (void)printf("%d %c %d =   ", left, op, right);
        (void)fflush(stdout);
        (void)time(&start);

        /*
         * Keep looping until the correct answer is given, or until EOF or
         * interrupt is typed.
         */
        for (;;) {
                if (!fgets(line, sizeof(line), stdin)) {
                        (void)printf("\n");
                        return(EOF);
                }
                for (p = line; *p && isspace(*p); ++p);
                if (!isdigit(*p)) {
                        (void)printf("Please type a number.\n");
                        continue;
                }
                if (atoi(p) == result) {
                        (void)printf("Right!\n");
                        ++nright;
                        break;
                }
                /* Wrong answer; penalise and ask again. */
                (void)printf("What?\n");
                ++nwrong;
                penalise(right, op, 1);
                if (op == 'x' || op == '+')
                        penalise(left, op, 0);
                else
                        penalise(result, op, 0);
        }

        /*
         * Accumulate the time taken.  Obviously rounding errors happen here;
         * however they should cancel out, because some of the time you are
         * charged for a partially elapsed second at the start, and some of
         * the time you are not charged for a partially elapsed second at the
         * end.
         */
        (void)time(&finish);
        qtime += finish - start;
        return(0);
}

/*
 * Here is the code for accumulating penalties against the numbers for which
 * a wrong answer was given.  The right operand and either the left operand
 * (for +, x) or the result (for -, /) are stored in a list for the particular
 * operation, and each becomes more likely to appear again in that operation.
 * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
 * many extra chances of appearing.  Each time it is selected because of this,
 * its penalty is decreased by one; it is removed when it reaches 0.
 *
 * The penalty[] array gives the sum of all penalties in the list for
 * each operation and each operand.  The penlist[] array has the lists of
 * penalties themselves.
 */

int penalty[sizeof(keylist) - 1][2];
struct penalty {
        int value, penalty;     /* Penalised value and its penalty. */
        struct penalty *next;
} *penlist[sizeof(keylist) - 1][2];

#define WRONGPENALTY    5       /* Perhaps this should depend on maxrange. */

/*
 * Add a penalty for the number `value' to the list for operation `op',
 * operand number `operand' (0 or 1).  If we run out of memory, we just
 * forget about the penalty (how likely is this, anyway?).
 */
penalise(value, op, operand)
        int value, op, operand;
{
        struct penalty *p;
        char *malloc();

        op = opnum(op);
        if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL)
                return;
        p->next = penlist[op][operand];
        penlist[op][operand] = p;
        penalty[op][operand] += p->penalty = WRONGPENALTY;
        p->value = value;
}

/*
 * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
 * of operation `op'.  The random number we generate is either used directly
 * as a value, or represents a position in the penalty list.  If the latter,
 * we find the corresponding value and return that, decreasing its penalty.
 */
getrandom(maxval, op, operand)
        int maxval, op, operand;
{
        int value;
        register struct penalty **pp, *p;

        op = opnum(op);
        value = random() % (maxval + penalty[op][operand]);

        /*
         * 0 to maxval - 1 is a number to be used directly; bigger values
         * are positions to be located in the penalty list.
         */
        if (value < maxval)
                return(value);
        value -= maxval;

        /*
         * Find the penalty at position `value'; decrement its penalty and
         * delete it if it reaches 0; return the corresponding value.
         */
        for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
                if (p->penalty > value) {
                        value = p->value;
                        penalty[op][operand]--;
                        if (--(p->penalty) <= 0) {
                                p = p->next;
                                (void)free((char *)*pp);
                                *pp = p;
                        }
                        return(value);
                }
                value -= p->penalty;
        }
        /*
         * We can only get here if the value from the penalty[] array doesn't
         * correspond to the actual sum of penalties in the list.  Provide an
         * obscure message.
         */
        (void)fprintf(stderr, "arithmetic: bug: inconsistent penalties\n");
        exit(1);
        /* NOTREACHED */
}

/* Return an index for the character op, which is one of [+-x/]. */
opnum(op)
        int op;
{
        char *p;

        if (op == 0 || (p = index(keylist, op)) == NULL) {
                (void)fprintf(stderr,
                    "arithmetic: bug: op %c not in keylist %s\n", op, keylist);
                exit(1);
        }
        return(p - keylist);
}

/* Print usage message and quit. */
usage()
{
        (void)fprintf(stderr, "usage: arithmetic [-o +-x/] [-r range]\n");
        exit(1);
}