%{
#include <stdio.h>
int id=0, op=0, ob=0, cb=0;
%}
 
%%
[a-zA-Z0-9]+    { id++; printf("Identifier: %s\n", yytext); }
[+\-*/]         { op++; }
"("             { ob++; }
")"             { cb++; }
.|\n            ;
%%
 
int yywrap() { return 1; }
 
int main() {
    printf("Enter expression: ");
    yylex();
    // Basic validation: Brackets must match, and usually identifiers = operators + 1
    if(ob == cb && id == op + 1) 
        printf("Valid expression\n");
    else 
        printf("Invalid expression\n");
    return 0;
}

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