valid expression.l

// lex file

%{ 
/* 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; 
} 

// yacc file


%{ 
/* Definition section */
#include<stdio.h> 
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 Any Arithmetic Expression which 
				can have operations Addition, 
				Subtraction, Multiplication, Division, 
						Modulus and Round brackets:\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; 
}