1 /* 2 * Copyright (c) 1989 The Regents of the University of California. 3 * 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 are permitted 9 * provided that the above copyright notice and this paragraph are 10 * duplicated in all such forms and that any documentation, 11 * advertising materials, and other materials related to such 12 * distribution and use acknowledge that the software was developed 13 * by the University of California, Berkeley. The name of the 14 * University may not be used to endorse or promote products derived 15 * from this software without specific prior written permission. 16 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 18 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 19 */ 20 21 #ifndef lint 22 char copyright[] = 23 "@(#) Copyright (c) 1989 The Regents of the University of California.\n\ 24 All rights reserved.\n"; 25 #endif /* not lint */ 26 27 #ifndef lint 28 static char sccsid[] = "@(#)arithmetic.c 5.2 (Berkeley) 09/13/89"; 29 #endif /* not lint */ 30 31 /* 32 * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>. 33 * 34 * The operation of this program mimics that of the standard Unix game 35 * `arithmetic'. I've made it as close as I could manage without examining 36 * the source code. The principal differences are: 37 * 38 * The method of biasing towards numbers that had wrong answers in the past 39 * is different; original `arithmetic' seems to retain the bias forever, 40 * whereas this program lets the bias gradually decay as it is used. 41 * 42 * Original `arithmetic' delays for some period (3 seconds?) after printing 43 * the score. I saw no reason for this delay, so I scrapped it. 44 * 45 * There is no longer a limitation on the maximum range that can be supplied 46 * to the program. The original program required it to be less than 100. 47 * Anomalous results may occur with this program if ranges big enough to 48 * allow overflow are given. 49 * 50 * I have obviously not attempted to duplicate bugs in the original. It 51 * would go into an infinite loop if invoked as `arithmetic / 0'. It also 52 * did not recognise an EOF in its input, and would continue trying to read 53 * after it. It did not check that the input was a valid number, treating any 54 * garbage as 0. Finally, it did not flush stdout after printing its prompt, 55 * so in the unlikely event that stdout was not a terminal, it would not work 56 * properly. 57 */ 58 59 #include <sys/types.h> 60 #include <sys/signal.h> 61 #include <ctype.h> 62 #include <stdio.h> 63 #include <strings.h> 64 65 char keylist[] = "+-x/"; 66 char defaultkeys[] = "+-"; 67 char *keys = defaultkeys; 68 int nkeys = sizeof(defaultkeys) - 1; 69 int rangemax = 10; 70 int nright, nwrong; 71 time_t qtime; 72 #define NQUESTS 20 73 74 /* 75 * Select keys from +-x/ to be asked addition, subtraction, multiplication, 76 * and division problems. More than one key may be given. The default is 77 * +-. Specify a range to confine the operands to 0 - range. Default upper 78 * bound is 10. After every NQUESTS questions, statistics on the performance 79 * so far are printed. 80 */ 81 void 82 main(argc, argv) 83 int argc; 84 char **argv; 85 { 86 extern char *optarg; 87 extern int optind; 88 int ch, cnt; 89 time_t time(); 90 sig_t intr(); 91 92 while ((ch = getopt(argc, argv, "r:o:")) != EOF) 93 switch(ch) { 94 case 'o': { 95 register char *p; 96 97 for (p = keys = optarg; *p; ++p) 98 if (!index(keylist, *p)) { 99 (void)fprintf(stderr, 100 "arithmetic: unknown key.\n"); 101 exit(1); 102 } 103 nkeys = p - optarg; 104 break; 105 } 106 case 'r': 107 if ((rangemax = atoi(optarg)) <= 0) { 108 (void)fprintf(stderr, 109 "arithmetic: invalid range.\n"); 110 exit(1); 111 } 112 break; 113 case '?': 114 default: 115 usage(); 116 } 117 if (argc -= optind) 118 usage(); 119 120 /* Seed the random-number generator. */ 121 srandom((int)time((time_t *)NULL)); 122 123 (void)signal(SIGINT, intr); 124 125 /* Now ask the questions. */ 126 for (;;) { 127 for (cnt = NQUESTS; cnt--;) 128 if (problem() == EOF) 129 exit(0); 130 showstats(); 131 } 132 /* NOTREACHED */ 133 } 134 135 /* Handle interrupt character. Print score and exit. */ 136 sig_t 137 intr() 138 { 139 showstats(); 140 exit(0); 141 } 142 143 /* Print score. Original `arithmetic' had a delay after printing it. */ 144 showstats() 145 { 146 if (nright + nwrong > 0) { 147 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%", 148 nright, nwrong, (int)(100L * nright / (nright + nwrong))); 149 if (nright > 0) 150 (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n", 151 (long)qtime, (float)qtime / nright); 152 } 153 (void)printf("\n"); 154 } 155 156 /* 157 * Pick a problem and ask it. Keeps asking the same problem until supplied 158 * with the correct answer, or until EOF or interrupt is typed. Problems are 159 * selected such that the right operand and either the left operand (for +, x) 160 * or the correct result (for -, /) are in the range 0 to rangemax. Each wrong 161 * answer causes the numbers in the problem to be penalised, so that they are 162 * more likely to appear in subsequent problems. 163 */ 164 problem() 165 { 166 register char *p; 167 time_t start, finish; 168 int left, op, right, result; 169 char line[80]; 170 171 op = keys[random() % nkeys]; 172 if (op != '/') 173 right = getrandom(rangemax + 1, op, 1); 174 retry: 175 /* Get the operands. */ 176 switch (op) { 177 case '+': 178 left = getrandom(rangemax + 1, op, 0); 179 result = left + right; 180 break; 181 case '-': 182 result = getrandom(rangemax + 1, op, 0); 183 left = right + result; 184 break; 185 case 'x': 186 left = getrandom(rangemax + 1, op, 0); 187 result = left * right; 188 break; 189 case '/': 190 right = getrandom(rangemax, op, 1) + 1; 191 result = getrandom(rangemax + 1, op, 0); 192 left = right * result + random() % right; 193 break; 194 } 195 196 /* 197 * A very big maxrange could cause negative values to pop 198 * up, owing to overflow. 199 */ 200 if (result < 0 || left < 0) 201 goto retry; 202 203 (void)printf("%d %c %d = ", left, op, right); 204 (void)fflush(stdout); 205 (void)time(&start); 206 207 /* 208 * Keep looping until the correct answer is given, or until EOF or 209 * interrupt is typed. 210 */ 211 for (;;) { 212 if (!fgets(line, sizeof(line), stdin)) { 213 (void)printf("\n"); 214 return(EOF); 215 } 216 for (p = line; *p && isspace(*p); ++p); 217 if (!isdigit(*p)) { 218 (void)printf("Please type a number.\n"); 219 continue; 220 } 221 if (atoi(p) == result) { 222 (void)printf("Right!\n"); 223 ++nright; 224 break; 225 } 226 /* Wrong answer; penalise and ask again. */ 227 (void)printf("What?\n"); 228 ++nwrong; 229 penalise(right, op, 1); 230 if (op == 'x' || op == '+') 231 penalise(left, op, 0); 232 else 233 penalise(result, op, 0); 234 } 235 236 /* 237 * Accumulate the time taken. Obviously rounding errors happen here; 238 * however they should cancel out, because some of the time you are 239 * charged for a partially elapsed second at the start, and some of 240 * the time you are not charged for a partially elapsed second at the 241 * end. 242 */ 243 (void)time(&finish); 244 qtime += finish - start; 245 return(0); 246 } 247 248 /* 249 * Here is the code for accumulating penalties against the numbers for which 250 * a wrong answer was given. The right operand and either the left operand 251 * (for +, x) or the result (for -, /) are stored in a list for the particular 252 * operation, and each becomes more likely to appear again in that operation. 253 * Initially, each number is charged a penalty of WRONGPENALTY, giving it that 254 * many extra chances of appearing. Each time it is selected because of this, 255 * its penalty is decreased by one; it is removed when it reaches 0. 256 * 257 * The penalty[] array gives the sum of all penalties in the list for 258 * each operation and each operand. The penlist[] array has the lists of 259 * penalties themselves. 260 */ 261 262 int penalty[sizeof(keylist) - 1][2]; 263 struct penalty { 264 int value, penalty; /* Penalised value and its penalty. */ 265 struct penalty *next; 266 } *penlist[sizeof(keylist) - 1][2]; 267 268 #define WRONGPENALTY 5 /* Perhaps this should depend on maxrange. */ 269 270 /* 271 * Add a penalty for the number `value' to the list for operation `op', 272 * operand number `operand' (0 or 1). If we run out of memory, we just 273 * forget about the penalty (how likely is this, anyway?). 274 */ 275 penalise(value, op, operand) 276 int value, op, operand; 277 { 278 struct penalty *p; 279 char *malloc(); 280 281 op = opnum(op); 282 if ((p = (struct penalty *)malloc((u_int)sizeof(*p))) == NULL) 283 return; 284 p->next = penlist[op][operand]; 285 penlist[op][operand] = p; 286 penalty[op][operand] += p->penalty = WRONGPENALTY; 287 p->value = value; 288 } 289 290 /* 291 * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1) 292 * of operation `op'. The random number we generate is either used directly 293 * as a value, or represents a position in the penalty list. If the latter, 294 * we find the corresponding value and return that, decreasing its penalty. 295 */ 296 getrandom(maxval, op, operand) 297 int maxval, op, operand; 298 { 299 int value; 300 register struct penalty **pp, *p; 301 302 op = opnum(op); 303 value = random() % (maxval + penalty[op][operand]); 304 305 /* 306 * 0 to maxval - 1 is a number to be used directly; bigger values 307 * are positions to be located in the penalty list. 308 */ 309 if (value < maxval) 310 return(value); 311 value -= maxval; 312 313 /* 314 * Find the penalty at position `value'; decrement its penalty and 315 * delete it if it reaches 0; return the corresponding value. 316 */ 317 for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) { 318 if (p->penalty > value) { 319 value = p->value; 320 penalty[op][operand]--; 321 if (--(p->penalty) <= 0) { 322 p = p->next; 323 (void)free((char *)*pp); 324 *pp = p; 325 } 326 return(value); 327 } 328 value -= p->penalty; 329 } 330 /* 331 * We can only get here if the value from the penalty[] array doesn't 332 * correspond to the actual sum of penalties in the list. Provide an 333 * obscure message. 334 */ 335 (void)fprintf(stderr, "arithmetic: bug: inconsistent penalties\n"); 336 exit(1); 337 /* NOTREACHED */ 338 } 339 340 /* Return an index for the character op, which is one of [+-x/]. */ 341 opnum(op) 342 int op; 343 { 344 char *p; 345 346 if (op == 0 || (p = index(keylist, op)) == NULL) { 347 (void)fprintf(stderr, 348 "arithmetic: bug: op %c not in keylist %s\n", op, keylist); 349 exit(1); 350 } 351 return(p - keylist); 352 } 353 354 /* Print usage message and quit. */ 355 usage() 356 { 357 (void)fprintf(stderr, "usage: arithmetic [-o +-x/] [-r range]\n"); 358 exit(1); 359 } 360