simple calculator yacc program

cal.lex

**************************

 %{

/* Definition section */

#include<stdio.h>

#include "cal.tab.h"

extern int yylval;

%}

%option noyywrap

/* Rule Section */

%%

[0-9]+ {

                yylval=atoi(yytext);

                return NUMBER;

        }

[\t] ;

[\n] return 0;

. return yytext[0];

%%

cal.y

*********************************************

%{

/* Definition section */

#include<stdio.h>

int flag=0;

void yyerror();

%}

%token NUMBER

%left '+' '-'

%left '*' '/' '%'

%left '(' ')'

/* Rule Section */

%%

S: E{

                printf("\nResult=%d\n", $$);

                return 0;

                };

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

        |E'-'E {$$=$1-$3;}

        |E'*'E {$$=$1*$3;}

        |E'/'E {$$=$1/$3;}

        |E'%'E {$$=$1%$3;}

        |'('E')' {$$=$2;}

        | NUMBER {$$=$1;}

;

%%

//driver code

void main()

{

printf("\nEnter Any Arithmetic Expression\n");

yyparse();

if(flag==0)

printf("\nEntered arithmetic expression is Valid\n\n");

}

void yyerror()

{

printf("\nEntered arithmetic expression is Invalid\n\n");

flag=1;

}

Execution

**************

$ bison -d cal.y

$ lex cal.lex

$ gcc lex.yy.c cal.tab.c

$ ./a.out

Enter Any Arithmetic Expression

(2+3)*2

Result=10

Entered arithmetic expression is Valid

(base) [ftpb07@login01 yacc]$ ./a.out

Enter Any Arithmetic Expression

2-3*2

Result=-4

Entered arithmetic expression is Valid

(base) [ftpb07@login01 yacc]$ ./a.out

Enter Any Arithmetic Expression

5/3-2*2

Result=-3

Entered arithmetic expression is Valid

Enter Any Arithmetic Expression

2-3+

Entered arithmetic expression is Invalid