Working with the Unix OS

Development Tools
*/
%{
#define YYSTYPE double /* data type for yacc stack */
#include
#include
char *progname;
int lineno=1;
%}
%token NUMBER
%left '+' '-' /* left associative, same precedence */
%left '*' '/' /* left assoc., higher precedence */
%%
list: /* nothing */
| list '\n'
| list expr '\n' { printf("\t%.8g\n", $2);}
;
expr:
NUMBER
| expr '+' expr {$$ =$1 + $3;}
| expr '-' expr {$$ =$1 - $3;}
| expr '*' expr {$$ =$1 * $3;}
| expr '/' expr {$$ =$1 / $3;}
| '(' expr ')' {$$ =$2;}
;
%% /*end of grammar */
main(int argc, char *argv[] )
{
progname = argv[0];
yyparse();
}
yylex()
{
int c;
while ((c=getchar() == ' ' || c == '\t');
}
if (c == EOF)
return 0;
if (c == '.' || isdigit(c))
{
ungetc(c, stdin);
scanf("%1f", &&yylval);
return NUMBER;
}
if (c == '\n')
lineno++;
return c;
yyerror(char *s)
{
warning(s, (char *) 0);
}
warning(char *s, char *t)
{
fprintf(stderr, "%s: %s", progname, s);
if (t)
fprintf(stderr, " %s", t);
fprintf(stderr, "near line $d\n", lineno);
62