plz mention me the errors i dont understand what i do..

#include<fstream>
#include<iostream>
#include<string>
#include<ctype.h>

#define _TABSIZE    4

using namespace std;

int tabsize = _TABSIZE;

class token {
public:
    token() : _what(code) {}
public:
    enum type {code, comment, pp, keyword};
    string _str;
    type _what;
    friend istream& operator>>(istream&, token&);
    friend ostream& operator<<(ostream&, const token&);
};

bool iskeyword(const string& s)
{
    static const char* keywords[] = {
        "and",
        "and_eq",
        "asm",
        "auto",
        "bitand",
        "bitor",
        "bool",
        "break",
        "case",
        "catch",
        "char",
        "class",
        "compl",
        "const",
        "const_cast",
        "continue",
        "default",
        "delete",
        "do",
        "double",
        "dynamic_cast",
        "else",
        "enum",
        "explicit",
        "export",
        "extern",
        "false",
        "float",
        "for",
        "friend",
        "goto",
        "if",
        "inline",
        "int",
        "long",
        "mutable",
        "namespace",
        "new",
        "not",
        "not_eq",
        "operator",
        "or",
        "or_eq",
        "private",
        "protected",
        "public",
        "register",
        "reinterpret_cast",
        "return",
        "short",
        "signed",
        "sizeof",
        "static",
        "static_cast",
        "struct",
        "switch",
        "template",
        "this",
        "throw",
        "true",
        "try",
        "typedef",
        "typeid",
        "typename",
        "union",
        "unsigned",
        "using",
        "virtual",
        "void",
        "volatile",
        "wchar_t",
        "while",
        "xor",
        "xor_eq"
    };

    for (int i = 0; i < sizeof(keywords) / sizeof(char*); i++)
        if (string(keywords[i]) == s)
            return true;

    return false;
}

bool containspp(const string& s)
{
    static const char* pptokens[] = {
        "define",
        "elif",
        "else",
        "endif",
        "error",
        "if",
        "ifdef",
        "ifndef",
        "include",
        "line",
        "pragma",
        "undef"
    };

    for (int i = 0; i < sizeof(pptokens) / sizeof(char*); i++)
        if (s.find(pptokens[i]) != string::npos)
            return true;

    return false;
}

istream& operator>>(istream& is, token& t)
{
    t._str = "", t._what = token::code;
    int c = is.get();
    switch (c) {
        case '/':
            c = is.get();
            if (c == '*') {
                t._str = "/*";
                t._what = token::comment;
                while (1) {
                    c = is.get();
                    if (c == EOF)
                        return is.unget(), is.clear(), is;
                    if (c == '/') {
                        if (t._str.length() > 2 &&
                            t._str[t._str.length() - 1] == '*') {
                            return t._str += '/', is;
                        }
                    }
                    t._str += (char)c;
                }
            } else if (c == '/') {
                t._str = "//";
                t._what = token::comment;
                c = is.get();
                while (c != '\n' && c != EOF) {
                    t._str += (char)c;
                    c = is.get();
                }
                if (c == '\n') {
                    t._str += '\n';
                }
                return is;
            }
            t._str = '/';
            return is.unget(), is.clear(), is;
        case '#':
            t._str = '#';
            c = is.get();
            while (strchr(" \r\n\t", c)) {
                t._str += (char)c;
                c = is.get();
            }
            if (c == EOF)
                return is.unget(), is.clear(), is;
            while (strchr("abcdefghijklmnopqrstuvwxyz", c)) {
                t._str += (char)c;
                c = is.get();
            }
            is.unget(), is.clear();
            if (containspp(t._str))
                t._what = token::pp;
            return is;
        case '\'':
        case '"': {
            char q = (char)c;
            t._str = q;
            while (1) {
                c = is.get();
                if (c == EOF)
                    return is.unget(), is.clear(), is;
                if (c == q) {
                    if (t._str.length() >= 2) {
                        if (!(t._str[t._str.length() - 1] == '\\' &&
                            t._str[t._str.length() - 2] != '\\'))
                            return t._str += q, is;
                    } else {
                        return t._str += q, is;
                    }
                }
                t._str += (char)c;                
            }
        }
        case 'a':
        case 'b':
        case 'c':
        case 'd':
        case 'e':
        case 'f':
        case 'g':
        case 'i':
        case 'l':
        case 'm':
        case 'n':
        case 'o':
        case 'p':
        case 'r':
        case 's':
        case 't':
        case 'u':
        case 'v':
        case 'w':
        case 'x':
            t._str += (char)c;
            c = is.get();
            while (isalpha(c) || isdigit(c) || c == '_') {
                t._str += (char)c;
                c = is.get();
            }
            is.unget(), is.clear();
            if (iskeyword(t._str))
                t._what = token::keyword;
            return is;
        case EOF:
            return is;
        default:
            t._str += (char)c;
            c = is.get();
            while (c != '/' && c != '#' && !strchr("abcdefgilmnoprstuvwx", c) &&
                c != '\'' && c != '"' && c != EOF) {
                t._str += (char)c;
                c = is.get();
            }
            is.unget(), is.clear();
            return is;
    }
}


string html(const string& s)
{
    string s1;
    string::size_type i;
    for (i = 0; i < s.length(); i++) {
        switch (s[i]) {
            case '&':
                s1 += "&";
                break;
            case '<':
                s1 += "<";
                break;
            case '>':
                s1 += ">";
                break;
            case '"':
                s1 += '"';
                break;
            case '\t':
                s1.append(tabsize, ' ');
                break;
            default:
                s1 += s[i];
        }
    }
    return s1;
}


ostream& operator<<(ostream& os, const token& t)
{
    if (t._what == token::code)
        cout << html(t._str);
    else if (t._what == token::comment)
        cout << "<span class=comment>" << html(t._str) << "</span>";
    else if (t._what == token::keyword)
        cout << "<span class=keyword>" << html(t._str) << "</span>";
    else if (t._what == token::pp)
        cout << "<span class=pp>" << html(t._str) << "</span>";
    else
        cout << html(t._str);
    return os;
}

int main(int argc, char **argv)
{
    if (argc != 2 && argc != 3) {
        cout << "usage: cpphtml file [tab size]" << endl;
        return 0;
    }
    ifstream is(argv[1]);
    if (!is.good()) {
        cout << "bad input file" << endl;
        return -1;
    }
    if (argc == 3) {
        tabsize = atoi(argv[2]);
        if (tabsize <= 0)
            tabsize = _TABSIZE;
    }
    cout << "<html>" << endl 
      << "<head>" << endl 
      << "<style>" << endl;
    cout << ".keyword{color:rgb(0,0,255);}" << endl;
    cout << ".comment{color:rgb(0,128,0);}" << endl;
    cout << ".pp{color:rgb(0,0,255);}" << endl;
    cout << "</style>" << endl << "<body>" << endl;
    cout << "<pre style=\"font-family:courier;font-size:10pt\">";
    token t;
    while(is >> t) {
        cout << t;
    }
    cout << "</pre>" << "</body>" 
         << endl << "</html>" << endl;
    return 0;
}

Please post the error or problem you are facing.

I got 2 errors:

1- Complaining that atoi is not defined(solution: #include <stdlib.h>)
2- 'strchr' is not defined, which is not really declared. So declare it before using it!!!

A Syntax Highlighter. I'm pretty sure it's not yours.
strchr() is defined in string.h/cstring

Oh, I didn't know that. I think it should a be good practice that, whenever string class is used, it should be included although on most compilers strings work without including.

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