prog3-1.y
%start line
%%
line : expr '\n' { printf("%d\n", $1); }
;
expr : expr '+' term { $$ = $1 + $3; }
| expr '-' term { $$ = $1 - $3; }
| term { $$ = $1; }
;
term : term '*' factor { $$ = $1 * $3; }
| term '/' factor { $$ = $1 / $3; }
| factor { $$ = $1; }
;
factor : '(' expr ')' { $$ = $2; }
| '0' { $$ = 0; }
| '1' { $$ = 1; }
| '2' { $$ = 2; }
| '3' { $$ = 3; }
| '4' { $$ = 4; }
| '5' { $$ = 5; }
| '6' { $$ = 6; }
| '7' { $$ = 7; }
| '8' { $$ = 8; }
| '9' { $$ = 9; }
;
%%
yylex()
{
int c;
while ((c = getchar()) == ' ');
return c;
}
prog3-2.y
%token NUM
%%
line : expr '\n' { printf("%d\n", $1); }
;
expr : expr '+' term { $$ = $1 + $3; }
| expr '-' term { $$ = $1 - $3; }
| term
;
term : term '*' factor { $$ = $1 * $3; }
| term '/' factor { $$ = $1 / $3; }
| factor
;
factor : '(' expr ')' { $$ = $2; }
| NUM
;
%%
#include <ctype.h>
yylex()
{
int c;
while ((c = getchar()) == ' ') ;
if (isdigit(c)) {
yylval = c - '0';
while (isdigit(c = getchar()))
yylval = yylval*10 + (c-'0');
ungetc(c, stdin);
return NUM; }
else
return c;
}