YACC PROGRAM to evaluate an arithmetic expression involving operators + - * /

program to evaluate an arithmetic expression involving operators + - * /

5a.l

%{

#include"y.tab.h"

extern int yylval;

%}

%%

[0-9]+ {yylval=atoi(yytext);

            return number;}

[\t] {;}

[\n] {return 0;}

. {return yytext[0];}

%%

5a.y file

%{

#include<stdio.h>

int res=0;

%}

%token number

%left '+' '-'

%left '*' '/'

%%

stmt:expr {res=$$;}

;

expr:expr '+' expr {$$=$1+$3;}

    |expr '-' expr {$$=$1-$3;}

    |expr '*' expr {$$=$1*$3;}

    |expr '/' expr {if($3==0)

             exit(0);

             else $$=$1/$3;}

    |number

    ;

%%

void main()

{

printf(" enter expr\n");

yyparse();

printf("valid=%d",res);

exit(0);

}

void yyerror()

{

printf("invalid\n");

exit(0);

}