Arithmetic expression Validator

## arith.l

/* lex program*/
%{
   /* Definition section */
  #include<stdio.h>
  #include "y.tab.h"
  //extern int yylval;
%}
  
/* Rule Section */
%%
[0-9]+ { yylval = atoi(yytext); /* yylval global variable used to pass the semantic value associated with a token from the lexer to the parser*/
          return NUMBER;
  
       }
[\t] ;
  
[\n] return 0;
  
. return yytext[0];
  
%%
  
int yywrap()
{
 return 1;
}


## arith.y

//Parser Source Code :

%{
   /* Definition section */
  #include<stdio.h>
  int flag=0;
%}
  
%token NUMBER  /*  %token used for terminal and token and %type can be used for Nonterminal name */

  
%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 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;
}