1 /* $NetBSD: arithmetic.c,v 1.27 2012/06/19 05:46:08 dholland 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
43 static char sccsid[] = "@(#)arithmetic.c 8.1 (Berkeley) 5/31/93";
44 #else
45 __RCSID("$NetBSD: arithmetic.c,v 1.27 2012/06/19 05:46:08 dholland 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
87 static int getrandom(int, int, int);
88 static void intr(int) __dead;
89 static int opnum(int);
90 static void penalise(int, int, int);
91 static int problem(void);
92 static void showstats(int);
93 static void usage(void) __dead;
94
95 static const char keylist[] = "+-x/";
96 static const char defaultkeys[] = "+-";
97 static const char *keys = defaultkeys;
98 static int nkeys = sizeof(defaultkeys) - 1;
99 static int rangemax = 10;
100 static int nright, nwrong;
101 static 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 */
111 int
main(int argc,char ** argv)112 main(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. */
157 static void
intr(int dummy __unused)158 intr(int dummy __unused)
159 {
160 showstats(1);
161 exit(0);
162 }
163
164 /* Print score. Original `arithmetic' had a delay after printing it. */
165 static void
showstats(int bool_sigint)166 showstats(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 */
190 static int
problem(void)191 problem(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);
202 retry:
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
290 static int penalty[sizeof(keylist) - 1][2];
291 static 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 */
303 static void
penalise(int value,int op,int operand)304 penalise(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 */
323 static int
getrandom(int maxval,int op,int operand)324 getrandom(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/]. */
367 static int
opnum(int op)368 opnum(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. */
379 static void
usage(void)380 usage(void)
381 {
382 (void)fprintf(stderr, "Usage: %s [-o +-x/] [-r range]\n",
383 getprogname());
384 exit(1);
385 }
386