%{
#include <stdio.h>
int a_count = 0, b_count = 0;
%}
 
%%
 
a        { a_count++; }
b        { b_count++; }
[^ab\n]  { printf("Invalid character: %s\n", yytext); }
\n       {
             if (a_count % 2 == 1 && b_count % 2 == 0) {
                 printf(" Accepted: Odd number of a's and Even number of b's\n");
             } else {
                 printf(" Rejected: a = %d, b = %d\n", a_count, b_count);
             }
             a_count = 0;
             b_count = 0;
         }
 
%%
 
int yywrap() {
    return 1;
}
 
int main() {
    printf("Enter strings (a/b only). Press Ctrl+D (Linux/Mac) or Ctrl+Z (Windows) to stop:\n");
    yylex();
    return 0;
}

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