1/*	$NetBSD: arithmetic.c,v 1.26 2011/08/31 16:24:55 plunky 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. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#include <sys/cdefs.h>
36#ifndef lint
37__COPYRIGHT("@(#) Copyright (c) 1989, 1993\
38 The Regents of the University of California.  All rights reserved.");
39#endif /* not lint */
40
41#ifndef lint
42#if 0
43static char sccsid[] = "@(#)arithmetic.c	8.1 (Berkeley) 5/31/93";
44#else
45__RCSID("$NetBSD: arithmetic.c,v 1.26 2011/08/31 16:24:55 plunky Exp $");
46#endif
47#endif /* not lint */
48
49/*
50 * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
51 *
52 * The operation of this program mimics that of the standard Unix game
53 * `arithmetic'.  I've made it as close as I could manage without examining
54 * the source code.  The principal differences are:
55 *
56 * The method of biasing towards numbers that had wrong answers in the past
57 * is different; original `arithmetic' seems to retain the bias forever,
58 * whereas this program lets the bias gradually decay as it is used.
59 *
60 * Original `arithmetic' delays for some period (3 seconds?) after printing
61 * the score.  I saw no reason for this delay, so I scrapped it.
62 *
63 * There is no longer a limitation on the maximum range that can be supplied
64 * to the program.  The original program required it to be less than 100.
65 * Anomalous results may occur with this program if ranges big enough to
66 * allow overflow are given.
67 *
68 * I have obviously not attempted to duplicate bugs in the original.  It
69 * would go into an infinite loop if invoked as `arithmetic / 0'.  It also
70 * did not recognise an EOF in its input, and would continue trying to read
71 * after it.  It did not check that the input was a valid number, treating any
72 * garbage as 0.  Finally, it did not flush stdout after printing its prompt,
73 * so in the unlikely event that stdout was not a terminal, it would not work
74 * properly.
75 */
76
77#include <sys/types.h>
78#include <err.h>
79#include <ctype.h>
80#include <signal.h>
81#include <stdio.h>
82#include <stdlib.h>
83#include <string.h>
84#include <time.h>
85#include <unistd.h>
86
87static int	getrandom(int, int, int);
88static void	intr(int) __dead;
89static int	opnum(int);
90static void	penalise(int, int, int);
91static int	problem(void);
92static void	showstats(int);
93static void	usage(void) __dead;
94
95static const char keylist[] = "+-x/";
96static const char defaultkeys[] = "+-";
97static const char *keys = defaultkeys;
98static int nkeys = sizeof(defaultkeys) - 1;
99static int rangemax = 10;
100static int nright, nwrong;
101static time_t qtime;
102#define	NQUESTS	20
103
104/*
105 * Select keys from +-x/ to be asked addition, subtraction, multiplication,
106 * and division problems.  More than one key may be given.  The default is
107 * +-.  Specify a range to confine the operands to 0 - range.  Default upper
108 * bound is 10.  After every NQUESTS questions, statistics on the performance
109 * so far are printed.
110 */
111int
112main(int argc, char **argv)
113{
114	int ch, cnt;
115
116	/* Revoke setgid privileges */
117	setgid(getgid());
118
119	while ((ch = getopt(argc, argv, "r:o:")) != -1)
120		switch(ch) {
121		case 'o': {
122			const char *p;
123
124			for (p = keys = optarg; *p; ++p)
125				if (!strchr(keylist, *p))
126					errx(1, "arithmetic: unknown key.");
127			nkeys = p - optarg;
128			break;
129		}
130		case 'r':
131			if ((rangemax = atoi(optarg)) <= 0)
132				errx(1, "arithmetic: invalid range.");
133			break;
134		case '?':
135		default:
136			usage();
137		}
138	if (argc -= optind)
139		usage();
140
141	/* Seed the random-number generator. */
142	srandom((int)time(NULL));
143
144	(void)signal(SIGINT, intr);
145
146	/* Now ask the questions. */
147	for (;;) {
148		for (cnt = NQUESTS; cnt--;)
149			if (problem() == EOF)
150				exit(0);
151		showstats(0);
152	}
153	/* NOTREACHED */
154}
155
156/* Handle interrupt character.  Print score and exit. */
157static void
158intr(int dummy __unused)
159{
160	showstats(1);
161	exit(0);
162}
163
164/* Print score.  Original `arithmetic' had a delay after printing it. */
165static void
166showstats(int bool_sigint)
167{
168	if (nright + nwrong > 0) {
169		(void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
170		    nright, nwrong, (int)(100L * nright / (nright + nwrong)));
171		if (nright > 0)
172	(void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
173			    (long)qtime, (float)qtime / nright);
174	}
175	if(!bool_sigint) {
176		(void)printf("Press RETURN to continue...\n");
177		while(!getchar()) ;
178	}
179	(void)printf("\n");
180}
181
182/*
183 * Pick a problem and ask it.  Keeps asking the same problem until supplied
184 * with the correct answer, or until EOF or interrupt is typed.  Problems are
185 * selected such that the right operand and either the left operand (for +, x)
186 * or the correct result (for -, /) are in the range 0 to rangemax.  Each wrong
187 * answer causes the numbers in the problem to be penalised, so that they are
188 * more likely to appear in subsequent problems.
189 */
190static int
191problem(void)
192{
193	char *p;
194	time_t start, finish;
195	int left, op, right, result;
196	char line[80];
197
198	right = left = result = 0;
199	op = keys[random() % nkeys];
200	if (op != '/')
201		right = getrandom(rangemax + 1, op, 1);
202retry:
203	/* Get the operands. */
204	switch (op) {
205	case '+':
206		left = getrandom(rangemax + 1, op, 0);
207		result = left + right;
208		break;
209	case '-':
210		result = getrandom(rangemax + 1, op, 0);
211		left = right + result;
212		break;
213	case 'x':
214		left = getrandom(rangemax + 1, op, 0);
215		result = left * right;
216		break;
217	case '/':
218		right = getrandom(rangemax, op, 1) + 1;
219		result = getrandom(rangemax + 1, op, 0);
220		left = right * result + random() % right;
221		break;
222	}
223
224	/*
225	 * A very big maxrange could cause negative values to pop
226	 * up, owing to overflow.
227	 */
228	if (result < 0 || left < 0)
229		goto retry;
230
231	(void)printf("%d %c %d =   ", left, op, right);
232	(void)fflush(stdout);
233	(void)time(&start);
234
235	/*
236	 * Keep looping until the correct answer is given, or until EOF or
237	 * interrupt is typed.
238	 */
239	for (;;) {
240		if (!fgets(line, sizeof(line), stdin)) {
241			(void)printf("\n");
242			return(EOF);
243		}
244		for (p = line; *p && isspace((unsigned char)*p); ++p);
245		if (!isdigit((unsigned char)*p)) {
246			(void)printf("Please type a number.\n");
247			continue;
248		}
249		if (atoi(p) == result) {
250			(void)printf("Right!\n");
251			++nright;
252			break;
253		}
254		/* Wrong answer; penalise and ask again. */
255		(void)printf("What?\n");
256		++nwrong;
257		penalise(right, op, 1);
258		if (op == 'x' || op == '+')
259			penalise(left, op, 0);
260		else
261			penalise(result, op, 0);
262	}
263
264	/*
265	 * Accumulate the time taken.  Obviously rounding errors happen here;
266	 * however they should cancel out, because some of the time you are
267	 * charged for a partially elapsed second at the start, and some of
268	 * the time you are not charged for a partially elapsed second at the
269	 * end.
270	 */
271	(void)time(&finish);
272	qtime += finish - start;
273	return(0);
274}
275
276/*
277 * Here is the code for accumulating penalties against the numbers for which
278 * a wrong answer was given.  The right operand and either the left operand
279 * (for +, x) or the result (for -, /) are stored in a list for the particular
280 * operation, and each becomes more likely to appear again in that operation.
281 * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
282 * many extra chances of appearing.  Each time it is selected because of this,
283 * its penalty is decreased by one; it is removed when it reaches 0.
284 *
285 * The penalty[] array gives the sum of all penalties in the list for
286 * each operation and each operand.  The penlist[] array has the lists of
287 * penalties themselves.
288 */
289
290static int penalty[sizeof(keylist) - 1][2];
291static struct penalty {
292	int value, penalty;	/* Penalised value and its penalty. */
293	struct penalty *next;
294} *penlist[sizeof(keylist) - 1][2];
295
296#define	WRONGPENALTY	5	/* Perhaps this should depend on maxrange. */
297
298/*
299 * Add a penalty for the number `value' to the list for operation `op',
300 * operand number `operand' (0 or 1).  If we run out of memory, we just
301 * forget about the penalty (how likely is this, anyway?).
302 */
303static void
304penalise(int value, int op, int operand)
305{
306	struct penalty *p;
307
308	op = opnum(op);
309	if ((p = malloc(sizeof(*p))) == NULL)
310		return;
311	p->next = penlist[op][operand];
312	penlist[op][operand] = p;
313	penalty[op][operand] += p->penalty = WRONGPENALTY;
314	p->value = value;
315}
316
317/*
318 * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
319 * of operation `op'.  The random number we generate is either used directly
320 * as a value, or represents a position in the penalty list.  If the latter,
321 * we find the corresponding value and return that, decreasing its penalty.
322 */
323static int
324getrandom(int maxval, int op, int operand)
325{
326	int value;
327	struct penalty **pp, *p;
328
329	op = opnum(op);
330	value = random() % (maxval + penalty[op][operand]);
331
332	/*
333	 * 0 to maxval - 1 is a number to be used directly; bigger values
334	 * are positions to be located in the penalty list.
335	 */
336	if (value < maxval)
337		return(value);
338	value -= maxval;
339
340	/*
341	 * Find the penalty at position `value'; decrement its penalty and
342	 * delete it if it reaches 0; return the corresponding value.
343	 */
344	for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
345		if (p->penalty > value) {
346			value = p->value;
347			penalty[op][operand]--;
348			if (--(p->penalty) <= 0) {
349				p = p->next;
350				(void)free((char *)*pp);
351				*pp = p;
352			}
353			return(value);
354		}
355		value -= p->penalty;
356	}
357	/*
358	 * We can only get here if the value from the penalty[] array doesn't
359	 * correspond to the actual sum of penalties in the list.  Provide an
360	 * obscure message.
361	 */
362	errx(1, "arithmetic: bug: inconsistent penalties.");
363	/* NOTREACHED */
364}
365
366/* Return an index for the character op, which is one of [+-x/]. */
367static int
368opnum(int op)
369{
370	char *p;
371
372	if (op == 0 || (p = strchr(keylist, op)) == NULL)
373		errx(1, "arithmetic: bug: op %c not in keylist %s",
374		    op, keylist);
375	return(p - keylist);
376}
377
378/* Print usage message and quit. */
379static void
380usage(void)
381{
382	(void)fprintf(stderr, "Usage: %s [-o +-x/] [-r range]\n",
383		getprogname());
384	exit(1);
385}
386