Calculator with lex, yacc

calc.l

%{
   /* Definition section */
  #include<stdio.h>
  #include "y.tab.h"
  extern int yylval;
%}

/* Rule Section */
%%
[0-9]+ {
          yylval=atoi(yytext);
          return NUMBER;

       }
[\t] ;

[\n] return 0;

. return yytext[0];

%%

int yywrap()
{
 return 1;
} 

calc.y

%{
/* Definition section */
  #include<stdio.h>
  int yylex();
  void yyerror();
  int flag=0;
%}

%token NUMBER

%left '+' '-'

%left '*' '/' '%'

%left '(' ')'

/* Rule Section */
%%

ArithmeticExpression: 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 Arithmetic Expression with operations +,-,*,%%,/ and ():\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;
}