Created
April 25, 2014 03:42
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sample 2
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#include <assert.h> | |
#include <ctype.h> | |
#include <stdlib.h> | |
#include <stdio.h> | |
static void bout(char *msg) __attribute__((noreturn)); | |
static int calc_expr(void); | |
static int calc_term(void); | |
static int calc_factor(void); | |
static void lex_init(void); | |
static void lex_next(void); | |
static int lex_token; | |
static int lex_nextchar; | |
int | |
main(void) | |
{ | |
for (;;) { | |
lex_init(); | |
if (lex_nextchar == EOF) { | |
break; | |
} else if (lex_nextchar != '\n') { | |
int tmp = calc_expr(); | |
printf("result: %d\n", tmp); | |
} | |
if (lex_nextchar != '\n') { | |
bout("unexpected input"); | |
} | |
} | |
return 0; | |
} | |
static void | |
bout(char *msg) /* bailout */ | |
{ | |
fprintf(stderr, "%s\n", msg); | |
exit(2); | |
} | |
/* | |
* calc | |
*/ | |
static int | |
calc_expr(void) | |
{ | |
/* EXPR = TERM (('+'|'-') TERM)* */ | |
int val = calc_term(); | |
while ((lex_nextchar == '+') || (lex_nextchar == '-')) { | |
int op, tmp; | |
lex_next(); | |
op = -lex_token; | |
tmp = calc_term(); | |
switch (op) { | |
case '+': | |
val += tmp; | |
break; | |
case '-': | |
val -= tmp; | |
break; | |
default: | |
assert(0); | |
} | |
} | |
return val; | |
} | |
static int | |
calc_term(void) | |
{ | |
/* TERM = FACTOR (('*'|'/') FACTOR)* */ | |
int val = calc_factor(); | |
while ((lex_nextchar == '*') || (lex_nextchar == '/')) { | |
int op, tmp; | |
lex_next(); | |
op = -lex_token; | |
tmp = calc_factor(); | |
switch (op) { | |
case '*': | |
val *= tmp; | |
break; | |
case '/': | |
val /= tmp; | |
break; | |
default: | |
assert(0); | |
} | |
} | |
return val; | |
} | |
static int | |
calc_factor(void) | |
{ | |
/* FACTOR = NUM | '(' EXPR ')' */ | |
if (isdigit(lex_nextchar)) { | |
lex_next(); | |
return lex_token; | |
} else if (lex_nextchar == '(') { /*)*/ | |
int tmp; | |
lex_next(); | |
assert(-lex_token == '('); /*)*/ | |
tmp = calc_expr(); | |
/*(*/ | |
if (lex_nextchar != ')') { | |
bout("syntax error"); | |
} | |
lex_next(); /*(*/ | |
assert(-lex_token == ')'); | |
return tmp; | |
} | |
bout("unexpected input"); | |
} | |
/* | |
* lex | |
*/ | |
static void | |
lex_init(void) | |
{ | |
do { | |
lex_nextchar = getchar(); | |
} while ((lex_nextchar != '\n') && isspace(lex_nextchar)); | |
} | |
static void | |
lex_next(void) | |
{ | |
if (isdigit(lex_nextchar)) { | |
lex_token = 0; | |
do { | |
lex_token = 10 * lex_token + digittoint(lex_nextchar); | |
lex_nextchar = getchar(); | |
} while (isdigit(lex_nextchar)); | |
} else if ((lex_nextchar == '+') || (lex_nextchar == '-') | |
|| (lex_nextchar == '*') || (lex_nextchar == '/') | |
|| (lex_nextchar == '(') || (lex_nextchar == ')')) { | |
lex_token = -lex_nextchar; | |
lex_nextchar = getchar(); | |
} else { | |
bout("unexpected input char"); | |
} | |
if (lex_nextchar == EOF) { | |
bout("unexpected EOF"); | |
} | |
while ((lex_nextchar != '\n') && isspace(lex_nextchar)) { | |
lex_nextchar = getchar(); | |
} | |
} |
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