1 /* $OpenBSD: arithmetic.c,v 1.27 2016/09/11 14:21:17 tb 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 /* 36 * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>. 37 * 38 * The operation of this program mimics that of the standard Unix game 39 * `arithmetic'. I've made it as close as I could manage without examining 40 * the source code. The principal differences are: 41 * 42 * The method of biasing towards numbers that had wrong answers in the past 43 * is different; original `arithmetic' seems to retain the bias forever, 44 * whereas this program lets the bias gradually decay as it is used. 45 * 46 * Original `arithmetic' delays for some period (3 seconds?) after printing 47 * the score. I saw no reason for this delay, so I scrapped it. 48 * 49 * There is no longer a limitation on the maximum range that can be supplied 50 * to the program. The original program required it to be less than 100. 51 * Anomalous results may occur with this program if ranges big enough to 52 * allow overflow are given. 53 * 54 * I have obviously not attempted to duplicate bugs in the original. It 55 * would go into an infinite loop if invoked as `arithmetic / 0'. It also 56 * did not recognise an EOF in its input, and would continue trying to read 57 * after it. It did not check that the input was a valid number, treating any 58 * garbage as 0. Finally, it did not flush stdout after printing its prompt, 59 * so in the unlikely event that stdout was not a terminal, it would not work 60 * properly. 61 */ 62 63 #include <err.h> 64 #include <ctype.h> 65 #include <limits.h> 66 #include <signal.h> 67 #include <stdio.h> 68 #include <stdlib.h> 69 #include <string.h> 70 #include <time.h> 71 #include <unistd.h> 72 73 int getrandom(int, int, int); 74 __dead void intr(int); 75 int opnum(int); 76 void penalise(int, int, int); 77 int problem(void); 78 void showstats(void); 79 __dead void usage(void); 80 81 const char keylist[] = "+-x/"; 82 const char defaultkeys[] = "+-"; 83 const char *keys = defaultkeys; 84 int nkeys = sizeof(defaultkeys) - 1; 85 int rangemax = 10; 86 int nright, nwrong; 87 time_t qtime; 88 #define NQUESTS 20 89 90 /* 91 * Select keys from +-x/ to be asked addition, subtraction, multiplication, 92 * and division problems. More than one key may be given. The default is 93 * +-. Specify a range to confine the operands to 0 - range. Default upper 94 * bound is 10. After every NQUESTS questions, statistics on the performance 95 * so far are printed. 96 */ 97 int 98 main(int argc, char *argv[]) 99 { 100 int ch, cnt; 101 const char *errstr; 102 103 if (pledge("stdio", NULL) == -1) 104 err(1, "pledge"); 105 106 while ((ch = getopt(argc, argv, "hr:o:")) != -1) 107 switch(ch) { 108 case 'o': { 109 const char *p; 110 111 for (p = keys = optarg; *p; ++p) 112 if (!strchr(keylist, *p)) 113 errx(1, "unknown key."); 114 nkeys = p - optarg; 115 break; 116 } 117 case 'r': 118 rangemax = strtonum(optarg, 1, INT_MAX, &errstr); 119 if (errstr) 120 errx(1, "invalid range, %s: %s", errstr, optarg); 121 break; 122 case 'h': 123 default: 124 usage(); 125 } 126 if (argc -= optind) 127 usage(); 128 129 (void)signal(SIGINT, intr); 130 131 /* Now ask the questions. */ 132 for (;;) { 133 for (cnt = NQUESTS; cnt--;) 134 if (problem() == EOF) 135 intr(0); /* Print score and exit */ 136 showstats(); 137 } 138 } 139 140 /* Handle interrupt character. Print score and exit. */ 141 void 142 intr(int dummy) 143 { 144 showstats(); 145 _exit(0); 146 } 147 148 /* Print score. Original `arithmetic' had a delay after printing it. */ 149 void 150 showstats(void) 151 { 152 if (nright + nwrong > 0) { 153 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%", 154 nright, nwrong, (int)(100L * nright / (nright + nwrong))); 155 if (nright > 0) 156 (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n", 157 (long)qtime, (float)qtime / nright); 158 } 159 (void)printf("\n"); 160 } 161 162 /* 163 * Pick a problem and ask it. Keeps asking the same problem until supplied 164 * with the correct answer, or until EOF or interrupt is typed. Problems are 165 * selected such that the right operand and either the left operand (for +, x) 166 * or the correct result (for -, /) are in the range 0 to rangemax. Each wrong 167 * answer causes the numbers in the problem to be penalised, so that they are 168 * more likely to appear in subsequent problems. 169 */ 170 int 171 problem(void) 172 { 173 char *p; 174 time_t start, finish; 175 int left, op, right, result; 176 char line[80]; 177 178 op = keys[arc4random_uniform(nkeys)]; 179 if (op != '/') 180 right = getrandom(rangemax + 1, op, 1); 181 retry: 182 /* Get the operands. */ 183 switch (op) { 184 case '+': 185 left = getrandom(rangemax + 1, op, 0); 186 result = left + right; 187 break; 188 case '-': 189 result = getrandom(rangemax + 1, op, 0); 190 left = right + result; 191 break; 192 case 'x': 193 left = getrandom(rangemax + 1, op, 0); 194 result = left * right; 195 break; 196 case '/': 197 right = getrandom(rangemax, op, 1) + 1; 198 result = getrandom(rangemax + 1, op, 0); 199 left = right * result + arc4random_uniform(right); 200 break; 201 } 202 203 /* 204 * A very big maxrange could cause negative values to pop 205 * up, owing to overflow. 206 */ 207 if (result < 0 || left < 0) 208 goto retry; 209 210 (void)printf("%d %c %d = ", left, op, right); 211 (void)fflush(stdout); 212 (void)time(&start); 213 214 /* 215 * Keep looping until the correct answer is given, or until EOF or 216 * interrupt is typed. 217 */ 218 for (;;) { 219 if (!fgets(line, sizeof(line), stdin)) { 220 (void)printf("\n"); 221 return(EOF); 222 } 223 for (p = line; isspace((unsigned char)*p); ++p); 224 if (!isdigit((unsigned char)*p)) { 225 (void)printf("Please type a number.\n"); 226 continue; 227 } 228 if (atoi(p) == result) { 229 (void)printf("Right!\n"); 230 ++nright; 231 break; 232 } 233 /* Wrong answer; penalise and ask again. */ 234 (void)printf("What?\n"); 235 ++nwrong; 236 penalise(right, op, 1); 237 if (op == 'x' || op == '+') 238 penalise(left, op, 0); 239 else 240 penalise(result, op, 0); 241 } 242 243 /* 244 * Accumulate the time taken. Obviously rounding errors happen here; 245 * however they should cancel out, because some of the time you are 246 * charged for a partially elapsed second at the start, and some of 247 * the time you are not charged for a partially elapsed second at the 248 * end. 249 */ 250 (void)time(&finish); 251 qtime += finish - start; 252 return(0); 253 } 254 255 /* 256 * Here is the code for accumulating penalties against the numbers for which 257 * a wrong answer was given. The right operand and either the left operand 258 * (for +, x) or the result (for -, /) are stored in a list for the particular 259 * operation, and each becomes more likely to appear again in that operation. 260 * Initially, each number is charged a penalty of WRONGPENALTY, giving it that 261 * many extra chances of appearing. Each time it is selected because of this, 262 * its penalty is decreased by one; it is removed when it reaches 0. 263 * 264 * The penalty[] array gives the sum of all penalties in the list for 265 * each operation and each operand. The penlist[] array has the lists of 266 * penalties themselves. 267 */ 268 269 int penalty[sizeof(keylist) - 1][2]; 270 struct penalty { 271 int value, penalty; /* Penalised value and its penalty. */ 272 struct penalty *next; 273 } *penlist[sizeof(keylist) - 1][2]; 274 275 #define WRONGPENALTY 5 /* Perhaps this should depend on maxrange. */ 276 277 /* 278 * Add a penalty for the number `value' to the list for operation `op', 279 * operand number `operand' (0 or 1). If we run out of memory, we just 280 * forget about the penalty (how likely is this, anyway?). 281 */ 282 void 283 penalise(int value, int op, int operand) 284 { 285 struct penalty *p; 286 287 op = opnum(op); 288 if ((p = malloc(sizeof(*p))) == NULL) 289 return; 290 p->next = penlist[op][operand]; 291 penlist[op][operand] = p; 292 penalty[op][operand] += p->penalty = WRONGPENALTY; 293 p->value = value; 294 } 295 296 /* 297 * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1) 298 * of operation `op'. The random number we generate is either used directly 299 * as a value, or represents a position in the penalty list. If the latter, 300 * we find the corresponding value and return that, decreasing its penalty. 301 */ 302 int 303 getrandom(int maxval, int op, int operand) 304 { 305 int value; 306 struct penalty **pp, *p; 307 308 op = opnum(op); 309 value = arc4random_uniform(maxval + penalty[op][operand]); 310 311 /* 312 * 0 to maxval - 1 is a number to be used directly; bigger values 313 * are positions to be located in the penalty list. 314 */ 315 if (value < maxval) 316 return(value); 317 value -= maxval; 318 319 /* 320 * Find the penalty at position `value'; decrement its penalty and 321 * delete it if it reaches 0; return the corresponding value. 322 */ 323 for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) { 324 if (p->penalty > value) { 325 value = p->value; 326 penalty[op][operand]--; 327 if (--(p->penalty) <= 0) { 328 p = p->next; 329 (void)free((char *)*pp); 330 *pp = p; 331 } 332 return(value); 333 } 334 value -= p->penalty; 335 } 336 /* 337 * We can only get here if the value from the penalty[] array doesn't 338 * correspond to the actual sum of penalties in the list. Provide an 339 * obscure message. 340 */ 341 errx(1, "bug: inconsistent penalties."); 342 } 343 344 /* Return an index for the character op, which is one of [+-x/]. */ 345 int 346 opnum(int op) 347 { 348 char *p; 349 350 if (op == 0 || (p = strchr(keylist, op)) == NULL) 351 errx(1, "bug: op %c not in keylist %s.", op, keylist); 352 return(p - keylist); 353 } 354 355 /* Print usage message and quit. */ 356 void 357 usage(void) 358 { 359 extern char *__progname; 360 (void)fprintf(stderr, "usage: %s [-o +-x/] [-r range]\n", __progname); 361 exit(1); 362 } 363