// re2c $INPUT -o $OUTPUT -i
#include <assert.h>
#include <float.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>

/*!max:re2c*/
static const size_t SIZE = 64 * 1024;

struct input_t {
    unsigned char buf[SIZE + YYMAXFILL];
    unsigned char *lim;
    unsigned char *cur;
    unsigned char *mar;
    unsigned char *tok;
    bool eof;

    FILE *const file;

    input_t(FILE *f)
        : buf()
        , lim(buf + SIZE)
        , cur(lim)
        , mar(lim)
        , tok(lim)
        , eof(false)
        , file(f)
    {}
    bool fill(size_t need)
    {
        if (eof) {
            return false;
        }
        const size_t free = tok - buf;
        if (free < need) {
            return false;
        }
        memmove(buf, tok, lim - tok);
        lim -= free;
        cur -= free;
        mar -= free;
        tok -= free;
        lim += fread(lim, 1, free, file);
        if (lim < buf + SIZE) {
            eof = true;
            memset(lim, 0, YYMAXFILL);
            lim += YYMAXFILL;
        }
        return true;
    }
};

/*!re2c re2c:define:YYCTYPE = "unsigned char"; */

template<int base>
static bool adddgt(unsigned long &u, unsigned long d)
{
    if (u > (ULONG_MAX - d) / base) {
        return false;
    }
    u = u * base + d;
    return true;
}

static bool lex_oct(const unsigned char *s, const unsigned char *e, unsigned long &u)
{
    for (u = 0, ++s; s < e; ++s) {
        if (!adddgt<8>(u, *s - 0x30u)) {
            return false;
        }
    }
    return true;
}

static bool lex_dec(const unsigned char *s, const unsigned char *e, unsigned long &u)
{
    for (u = 0; s < e; ++s) {
        if (!adddgt<10>(u, *s - 0x30u)) {
            return false;
        }
    }
    return true;
}

static bool lex_hex(const unsigned char *s, const unsigned char *e, unsigned long &u)
{
    for (u = 0, s += 2; s < e;) {
    /*!re2c
        re2c:yyfill:enable = 0;
        re2c:define:YYCURSOR = s;
        *     { if (!adddgt<16>(u, s[-1] - 0x30u))      return false; continue; }
        [a-f] { if (!adddgt<16>(u, s[-1] - 0x61u + 10)) return false; continue; }
        [A-F] { if (!adddgt<16>(u, s[-1] - 0x41u + 10)) return false; continue; }
    */
    }
    return true;
}

static bool lex_str(input_t &in, unsigned char q)
{
    fprintf(stderr, "%c", q);
    for (unsigned long u = q;; fprintf(stderr, "\\x%lx", u)) {
        in.tok = in.cur;
        /*!re2c
            re2c:define:YYCURSOR = in.cur;
            re2c:define:YYMARKER = in.mar;
            re2c:define:YYLIMIT = in.lim;
            re2c:yyfill:enable = 1;
            re2c:define:YYFILL = "if (!in.fill(@@)) return false;";
            re2c:define:YYFILL:naked = 1;
            *                    { return false; }
            [^\n\\]              { u = in.tok[0]; if (u == q) break; continue; }
            "\\a"                { u = '\a'; continue; }
            "\\b"                { u = '\b'; continue; }
            "\\f"                { u = '\f'; continue; }
            "\\n"                { u = '\n'; continue; }
            "\\r"                { u = '\r'; continue; }
            "\\t"                { u = '\t'; continue; }
            "\\v"                { u = '\v'; continue; }
            "\\\\"               { u = '\\'; continue; }
            "\\'"                { u = '\''; continue; }
            "\\\""               { u = '"';  continue; }
            "\\?"                { u = '?';  continue; }
            "\\" [0-7]{1,3}      { lex_oct(in.tok, in.cur, u); continue; }
            "\\u" [0-9a-fA-F]{4} { lex_hex(in.tok, in.cur, u); continue; }
            "\\U" [0-9a-fA-F]{8} { lex_hex(in.tok, in.cur, u); continue; }
            "\\x" [0-9a-fA-F]+   { if (!lex_hex(in.tok, in.cur, u)) return false; continue; }
        */
    }
    fprintf(stderr, "%c", q);
    return true;
}

static bool lex_flt(const unsigned char *s)
{
    double d = 0;
    double x = 1;
    int e = 0;
    /*!re2c
        re2c:yyfill:enable = 0;
        re2c:define:YYCURSOR = s;
    */
mant_int:
    /*!re2c
        "."   { goto mant_frac; }
        [eE]  { goto exp_sign; }
        *     { d = (d * 10) + (s[-1] - '0'); goto mant_int; }
    */
mant_frac:
    /*!re2c
        ""    { goto sfx; }
        [eE]  { goto exp_sign; }
        [0-9] { d += (x /= 10) * (s[-1] - '0'); goto mant_frac; }
    */
exp_sign:
    /*!re2c
        "+"?  { x = 1e+1; goto exp; }
        "-"   { x = 1e-1; goto exp; }
    */
exp:
    /*!re2c
        ""    { for (; e > 0; --e) d *= x;    goto sfx; }
        [0-9] { e = (e * 10) + (s[-1] - '0'); goto exp; }
    */
sfx:
    /*!re2c
        *     { goto end; }
        [fF]  { if (d > FLT_MAX) return false; goto end; }
    */
end:
    fprintf(stderr, "%g", d);
    return true;
}

static bool lex(input_t &in)
{
    unsigned long u;
    for (;;) {
        in.tok = in.cur;
        /*!re2c
            re2c:define:YYCURSOR = in.cur;
            re2c:define:YYMARKER = in.mar;
            re2c:define:YYLIMIT = in.lim;
            re2c:yyfill:enable = 1;
            re2c:define:YYFILL = "if (!in.fill(@@)) return false;";
            re2c:define:YYFILL:naked = 1;

            end = "\x00";

            *   { return false; }
            end {
                fprintf(stderr, "\n");
                return in.lim - in.tok == YYMAXFILL;
            }

            // macros
            macro = ("#" | "%:") ([^\n] | "\\\n")* "\n";
            macro { continue; }

            // whitespaces
            mcm = "/*" ([^*] | ("*" [^/]))* "*""/";
            scm = "//" [^\n]* "\n";
            wsp = ([ \t\v\n\r] | scm | mcm)+;
            wsp { fprintf(stderr, " "); continue; }

            // character and string literals
            "L"? ['"] { if (!lex_str(in, in.cur[-1])) return false; continue; }
            "L"? "''" { return false; }

            // integer literals
            oct = "0" [0-7]*;
            dec = [1-9][0-9]*;
            hex = '0x' [0-9a-fA-F]+;
            oct { if (!lex_oct(in.tok, in.cur, u)) return false; goto sfx; }
            dec { if (!lex_dec(in.tok, in.cur, u)) return false; goto sfx; }
            hex { if (!lex_hex(in.tok, in.cur, u)) return false; goto sfx; }

            // floating literals
            frc = [0-9]* "." [0-9]+ | [0-9]+ ".";
            exp = 'e' [+-]? [0-9]+;
            flt = (frc exp? | [0-9]+ exp) [fFlL]?;
            flt { if (lex_flt(in.tok)) continue; return false; }

            // boolean literals
            "false" { fprintf(stderr, "false"); continue; }
            "true"  { fprintf(stderr, "true");  continue; }

            // keywords
            "asm"              { fprintf(stderr, "ASM");              continue; }
            "auto"             { fprintf(stderr, "AUTO");             continue; }
            "bool"             { fprintf(stderr, "BOOL");             continue; }
            "break"            { fprintf(stderr, "BREAK");            continue; }
            "case"             { fprintf(stderr, "CASE");             continue; }
            "catch"            { fprintf(stderr, "CATCH");            continue; }
            "char"             { fprintf(stderr, "CHAR");             continue; }
            "class"            { fprintf(stderr, "CLASS");            continue; }
            "const"            { fprintf(stderr, "CONST");            continue; }
            "const_cast"       { fprintf(stderr, "CONST_CAST");       continue; }
            "continue"         { fprintf(stderr, "CONTINUE");         continue; }
            "default"          { fprintf(stderr, "DEFAULT");          continue; }
            "do"               { fprintf(stderr, "DO");               continue; }
            "double"           { fprintf(stderr, "DOUBLE");           continue; }
            "dynamic_cast"     { fprintf(stderr, "DYNAMIC_CAST");     continue; }
            "else"             { fprintf(stderr, "ELSE");             continue; }
            "enum"             { fprintf(stderr, "ENUM");             continue; }
            "explicit"         { fprintf(stderr, "EXPLICIT");         continue; }
            "export"           { fprintf(stderr, "EXPORT");           continue; }
            "extern"           { fprintf(stderr, "EXTERN");           continue; }
            "float"            { fprintf(stderr, "FLOAT");            continue; }
            "for"              { fprintf(stderr, "FOR");              continue; }
            "friend"           { fprintf(stderr, "FRIEND");           continue; }
            "goto"             { fprintf(stderr, "GOTO");             continue; }
            "if"               { fprintf(stderr, "IF");               continue; }
            "inline"           { fprintf(stderr, "INLINE");           continue; }
            "int"              { fprintf(stderr, "INT");              continue; }
            "long"             { fprintf(stderr, "LONG");             continue; }
            "mutable"          { fprintf(stderr, "MUTABLE");          continue; }
            "namespace"        { fprintf(stderr, "NAMESPACE");        continue; }
            "operator"         { fprintf(stderr, "OPERATOR");         continue; }
            "private"          { fprintf(stderr, "PRIVATE");          continue; }
            "protected"        { fprintf(stderr, "PROTECTED");        continue; }
            "public"           { fprintf(stderr, "PUBLIC");           continue; }
            "register"         { fprintf(stderr, "REGISTER");         continue; }
            "reinterpret_cast" { fprintf(stderr, "REINTERPRET_CAST"); continue; }
            "return"           { fprintf(stderr, "RETURN");           continue; }
            "short"            { fprintf(stderr, "SHORT");            continue; }
            "signed"           { fprintf(stderr, "SIGNED");           continue; }
            "sizeof"           { fprintf(stderr, "SIZEOF");           continue; }
            "static"           { fprintf(stderr, "STATIC");           continue; }
            "static_cast"      { fprintf(stderr, "STATIC_CAST");      continue; }
            "struct"           { fprintf(stderr, "STRUCT");           continue; }
            "switch"           { fprintf(stderr, "SWITCH");           continue; }
            "template"         { fprintf(stderr, "TEMPLATE");         continue; }
            "this"             { fprintf(stderr, "THIS");             continue; }
            "throw"            { fprintf(stderr, "THROW");            continue; }
            "try"              { fprintf(stderr, "TRY");              continue; }
            "typedef"          { fprintf(stderr, "TYPEDEF");          continue; }
            "typeid"           { fprintf(stderr, "TYPEID");           continue; }
            "typename"         { fprintf(stderr, "TYPENAME");         continue; }
            "union"            { fprintf(stderr, "UNION");            continue; }
            "unsigned"         { fprintf(stderr, "UNSIGNED");         continue; }
            "using"            { fprintf(stderr, "USING");            continue; }
            "virtual"          { fprintf(stderr, "VIRTUAL");          continue; }
            "void"             { fprintf(stderr, "VOID");             continue; }
            "volatile"         { fprintf(stderr, "VOLATILE");         continue; }
            "wchar_t"          { fprintf(stderr, "WCHAR_T");          continue; }
            "while"            { fprintf(stderr, "WHILE");            continue; }

            // operators and punctuation (including preprocessor)
            ("{" | "<%")      { fprintf(stderr, "{");      continue; }
            ("}" | "%>")      { fprintf(stderr, "}");      continue; }
            ("[" | "<:")      { fprintf(stderr, "[");      continue; }
            ("]" | ":>")      { fprintf(stderr, "]");      continue; }
            "("               { fprintf(stderr, "(");      continue; }
            ")"               { fprintf(stderr, ")");      continue; }
            ";"               { fprintf(stderr, ";");      continue; }
            ":"               { fprintf(stderr, ":");      continue; }
            "..."             { fprintf(stderr, "...");    continue; }
            "new"             { fprintf(stderr, "new");    continue; }
            "delete"          { fprintf(stderr, "delete"); continue; }
            "?"               { fprintf(stderr, "?");      continue; }
            "::"              { fprintf(stderr, "::");     continue; }
            "."               { fprintf(stderr, ".");      continue; }
            ".*"              { fprintf(stderr, ".");      continue; }
            "+"               { fprintf(stderr, "+");      continue; }
            "-"               { fprintf(stderr, "-");      continue; }
            "*"               { fprintf(stderr, "*");      continue; }
            "/"               { fprintf(stderr, "/");      continue; }
            "%"               { fprintf(stderr, "%%");     continue; }
            ("^" | "xor")     { fprintf(stderr, "^");      continue; }
            ("&" | "bitand")  { fprintf(stderr, "&");      continue; }
            ("|" | "bitor")   { fprintf(stderr, "|");      continue; }
            ("~" | "compl")   { fprintf(stderr, "~");      continue; }
            ("!" | "not")     { fprintf(stderr, "!");      continue; }
            "="               { fprintf(stderr, "=");      continue; }
            "<"               { fprintf(stderr, "<");      continue; }
            ">"               { fprintf(stderr, ">");      continue; }
            "+="              { fprintf(stderr, "+=");     continue; }
            "-="              { fprintf(stderr, "-=");     continue; }
            "*="              { fprintf(stderr, "*=");     continue; }
            "/="              { fprintf(stderr, "/=");     continue; }
            "%="              { fprintf(stderr, "%%=");    continue; }
            ("^=" | "xor_eq") { fprintf(stderr, "^=");     continue; }
            ("&=" | "and_eq") { fprintf(stderr, "&=");     continue; }
            ("|=" | "or_eq")  { fprintf(stderr, "|=");     continue; }
            "<<"              { fprintf(stderr, "<<");     continue; }
            ">>"              { fprintf(stderr, ">>");     continue; }
            ">>="             { fprintf(stderr, ">>=");    continue; }
            "<<="             { fprintf(stderr, "<<=");    continue; }
            "=="              { fprintf(stderr, "==");     continue; }
            ("!=" | "not_eq") { fprintf(stderr, "!=");     continue; }
            "<="              { fprintf(stderr, "<=");     continue; }
            ">="              { fprintf(stderr, ">=");     continue; }
            ("&&" | "and")    { fprintf(stderr, "&&");     continue; }
            ("||" | "or")     { fprintf(stderr, "||");     continue; }
            "++"              { fprintf(stderr, "++");     continue; }
            "--"              { fprintf(stderr, "--");     continue; }
            ","               { fprintf(stderr, ",");      continue; }
            "->*"             { fprintf(stderr, "->*");    continue; }
            "->"              { fprintf(stderr, "->");     continue; }

            // identifiers
            id = [a-zA-Z_][a-zA-Z_0-9]*;
            id { fprintf(stderr, "%.*s", (int)(in.cur - in.tok), in.tok); continue; }
        */
sfx:
        /*!re2c
            ""          { if (u > INT_MAX)  return false; fprintf(stderr, "%d",  static_cast<int>(u));      continue; }
            'u'         { if (u > UINT_MAX) return false; fprintf(stderr, "%u",  static_cast<unsigned>(u)); continue; }
            'l'         { if (u > LONG_MAX) return false; fprintf(stderr, "%ld", static_cast<long>(u));     continue; }
            'ul' | 'lu' { fprintf(stderr, "%lu", u); continue; }
        */
    }
}

int main()
{
    const char *fname = "example.cpp";
    FILE *f;

    // prepare input file
    f = fopen(fname, "w");
    fprintf(f,
        "#include<stdio.h>\n"
        "\n"
        "int main()\n"
        "{\n"
        "    int n;\n"
        "    printf(\"Enter the number:\\n\");\n"
        "    scanf(\"%%d\", &n);\n"
        "\n"
        "    int f = 1;\n"
        "    for(int i = 1; i <= n; ++i) {\n"
        "        f *= i;\n"
        "    }\n"
        "\n"
        "    printf(\"Factorial of %%d is %%d\\n\", n, f);\n"
        "    return 0;\n"
        "}\n"
        "\n");
    fclose(f);

    f = fopen(fname, "rb");
    input_t in(f);
    assert(lex(in));
    fclose(f);

    // cleanup
    remove(fname);
    return 0;
}