%{
#include <stdio.h>
#include <stdlib.h>
int valid = 1;
%}
 
%%
[0-9]+             { /* number */ }
[+\-*/]            { /* operators */ }
[ \t\n]            { /* skip whitespace */ }
.                  { valid = 0; /* invalid character */ }
%%
 
int main(int argc, char **argv) {
    printf("Enter an arithmetic expression:\n");
    yylex();
    if (valid)
        printf("Valid expression (syntactically simple check).\n");
    else
        printf("Invalid expression (unrecognized characters found).\n");
    return 0;
}
 
int yywrap() {
    return 1;
}
 

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