lex
%{
#include<stdio.h>
#include<stdlib.h>
#define TOKEN_ID 1
#define TOKEN_NUMBER 2
#define TOKEN_OPERATOR 3
#define TOKEN_KEYWORD 4
 
id[a-zA-Z][a-zA-Z0-9]*number[0-9]+operator[+*/-]
keyword(if|else|while|for)
%%
{id}{printf("TOKEN_ID:%s\n",yytext);return TOKEN_ID;}
{number}{printf("TOKEN_NUMBER:%s\n",yytext);return TOKEN_NUMBER;}
{operator}{printf("TOKEN_OPERATOR:%s\n",yytext);return TOKEN_OPERATOR;}
{keyword}{printf("TOKEN_KEYWORD:%s\n",yytext);return TOKEN_KEYWORD;}
[\t\n];
printf("error:invalid character'%c'\n",*yytext);
%%
int main()
{
yylex();
return 0;
}
int yywrap();
return 1;
%}

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aWYgeD01KzMqMg==

if x=5+3*2