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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