However, Repl.it doesn't support the `flex` command by default. As an alternative, you can use [Ideone](https://i...content-available-to-author-only...e.com/), which supports Lex.
 
 
Here's your updated code for Ideone:
 
 
```c
%option noyywrap
 
%{
#include <stdio.h>
%}
 
%%
 
[id][a-zA-Z_][a-zA-Z0-9_]* {printf("%s is an identifier\n", yytext);}
 
for|if|else|int|float|double|char|do|while {printf("%s is a keyword\n", yytext);}
 
[0-9]+("[.][0-9]+")?([eE][+-]?[0-9]+)? {printf("%s is a number\n", yytext);}
 
\n  ;
 
.   {printf("Invalid character: %c\n", *yytext);}
 
%%
 
int main() {
    yylex();
    printf("\n\n");
    return 0;
}

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

JXsKI2luY2x1ZGUgJmx0O3N0ZGlvLmgmZ3Q7CiNpbmNsdWRlICZsdDtzdGRsaWIuaCZndDsKI2luY2x1ZGUgJmx0O3N0cmluZy5oJmd0OwoKZW51bSBUT0tFTiB7IEZJTj0wLCBJRCwgRU5USUVSIH07CmludCB5eWxpbmVubzsKJX0KCiVvcHRpb24geXlsaW5lbm8KY2hpZmZyZSBbMC05XSsKJSUKe2NoaWZmcmV9ICAgcmV0dXJuIEVOVElFUjsKLiAgICAgICAgICAgcmV0dXJuIElEOwolJQppbnQgeXl3cmFwKCkgeyByZXR1cm4gMTsgfQoKaW50IG1haW4oKSB7CiAgd2hpbGUgKHl5bGV4KCkpOwogIHJldHVybiAwOwp9

%{
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

enum TOKEN { FIN=0, ID, ENTIER };
int yylineno;
%}

%option yylineno
chiffre [0-9]+
%%
{chiffre}   return ENTIER;
.           return ID;
%%
int yywrap() { return 1; }

int main() {
  while (yylex());
  return 0;
}