A LEX and Yacc program that recognizes a specific format

A LEX and Yacc program that recognizes a specific format

Format: A^n B^n 

Lex Program:

%option noyywrap
%{
#include "y.tab.h"
%}
%%

a return A;
b return B;
\n return('\n');
. return;
%%


Yacc Program:
%{
#include<stdio.h>
%}

%token A B
%%
statement: anbn'\n' {

   printf("\n Its a valid string!!!");
   return 0;
      }
anbn: A B

 |A anbn B
 ;
%%
main()
{
 printf("\n Enter some Valid String: ");
 yyparse();
}

yyerror(char *s)
{
 printf("\n Its not in anbn");
}