Напишите объяснение для программы
| Код |
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <ctype.h>
#include <assert.h>
int tok;
double tokval;
int next() {
for (;;) {
int c = getchar();
if (c == EOF || strchr("+-*/^()\n", c) != NULL) return tok = c;
if (isspace(c)) continue;
if (isdigit(c) || c == '.') {
ungetc(c, stdin);
scanf(" %lf", &tokval);
return tok = 'n';
}
fprintf(stderr, "Bad character: %c\n", c); abort();
}
}
void skip(int t) { assert(tok == t); next(); }
double expr();
// numpar ::= number | '(' expr ')'
double numpar() {
if (tok == 'n') { double x = tokval; skip('n'); return x; }
skip('('); double x = expr(); skip(')'); return x;
}
// factor ::= numpar | numpar '^' factor
double factor() {
double x = numpar();
if (tok == '^') { skip('^'); x = pow(x, factor()); }
return x;
}
// term ::= factor | term '*' factor | term '/' factor
double term() {
double x = factor();
for (;;) {
if (tok == '*') { skip('*'); x *= factor(); }
else if (tok == '/') { skip('/'); x /= factor(); }
else return x;
}
}
// expr ::= term | expr '+' term | expr '-' term
double expr() {
double x = term();
for (;;) {
if (tok == '+') { skip('+'); x += term(); }
else if (tok == '-') { skip('-'); x -= term(); }
else return x;
}
}
int main() {
next();
while (tok != EOF) {
if (tok == '\n') { skip('\n'); continue; }
printf("%.9g\n", expr());
}
return 0;
}
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