/* $OpenBSD: arithmetic.c,v 1.27 2016/09/11 14:21:17 tb Exp $ */
/*
* Copyright (c) 1989, 1993
* 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. 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.
*/
/*
* By Eamonn McManus, Trinity College Dublin .
*
* 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
#include
#include
#include
#include
#include
#include
#include
#include
int getrandom(int, int, int);
__dead void intr(int);
int opnum(int);
void penalise(int, int, int);
int problem(void);
void showstats(void);
__dead void usage(void);
const char keylist[] = "+-x/";
const char defaultkeys[] = "+-";
const 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.
*/
int
main(int argc, char *argv[])
{
int ch, cnt;
const char *errstr;
if (pledge("stdio", NULL) == -1)
err(1, "pledge");
while ((ch = getopt(argc, argv, "hr:o:")) != -1)
switch(ch) {
case 'o': {
const char *p;
for (p = keys = optarg; *p; ++p)
if (!strchr(keylist, *p))
errx(1, "unknown key.");
nkeys = p - optarg;
break;
}
case 'r':
rangemax = strtonum(optarg, 1, INT_MAX, &errstr);
if (errstr)
errx(1, "invalid range, %s: %s", errstr, optarg);
break;
case 'h':
default:
usage();
}
if (argc -= optind)
usage();
(void)signal(SIGINT, intr);
/* Now ask the questions. */
for (;;) {
for (cnt = NQUESTS; cnt--;)
if (problem() == EOF)
intr(0); /* Print score and exit */
showstats();
}
}
/* Handle interrupt character. Print score and exit. */
void
intr(int dummy)
{
showstats();
_exit(0);
}
/* Print score. Original `arithmetic' had a delay after printing it. */
void
showstats(void)
{
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.
*/
int
problem(void)
{
char *p;
time_t start, finish;
int left, op, right, result;
char line[80];
op = keys[arc4random_uniform(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 + arc4random_uniform(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; isspace((unsigned char)*p); ++p);
if (!isdigit((unsigned char)*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?).
*/
void
penalise(int value, int op, int operand)
{
struct penalty *p;
op = opnum(op);
if ((p = malloc(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.
*/
int
getrandom(int maxval, int op, int operand)
{
int value;
struct penalty **pp, *p;
op = opnum(op);
value = arc4random_uniform(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.
*/
errx(1, "bug: inconsistent penalties.");
}
/* Return an index for the character op, which is one of [+-x/]. */
int
opnum(int op)
{
char *p;
if (op == 0 || (p = strchr(keylist, op)) == NULL)
errx(1, "bug: op %c not in keylist %s.", op, keylist);
return(p - keylist);
}
/* Print usage message and quit. */
void
usage(void)
{
extern char *__progname;
(void)fprintf(stderr, "usage: %s [-o +-x/] [-r range]\n", __progname);
exit(1);
}