%{
#include <stdio.h>
%}
 
%%
"#include<stdio.h>"     { printf("# include<stdio.h> is a preprocessor\n"); }
 
/* Keywords */
"int"|"void"|"main"|"printf"   { printf("A keyword: %s\n", yytext); }
 
/* Identifiers */
[a-zA-Z_][a-zA-Z0-9_]*  { printf("An identifier: %s\n", yytext); }
 
/* Numbers */
[0-9]+                  { printf("An integer: %s\n", yytext); }
 
/* Operators */
[+\-*/=]                { printf("An operator : %s\n", yytext); }
 
/* Punctuation */
[(){};,]                { printf("%s is a punctuation\n", yytext); }
 
/* String literal */
\".*\"                  { printf("%s is a literalstring\n", yytext); }
 
/* Ignore spaces */
[ \t\n]                 ;
 
/* Anything else */
.                       { printf("Unknown: %s\n", yytext); }
 
%%
 
int main() {
    printf("Enter input:\n");
    yylex();
    return 0;
}

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# include<stdio.h>
void main()
{
int a;
A= 10 +2;

12

Printf(“%d”, a);
}