HttpParsing for hypertext

I am in process of getting all hierarchical links from a given link and validating them; This is the code I wrote. But I am not feeling it as efficient.

Reasons are:

1.For the non unique links which open same page, code is getting sub-links again and again

2.Is the code getting all links?

3.Is it making valid URLs from the sub-links it derived?

4.May be some other reasons about which I have no idea.

Please suggest me how to make this piece of code efficient . Thank you.

class Program

{

        public static ArrayList sublink = new ArrayList();
        public static ArrayList subtitle = new ArrayList();
        public static int ini = 0, len_o, len_n, counter = 0;
        static void Main(string[] args)
        {
         // Address of URL
            string URL = "http://www.techonthenet.com/"; 
        sublink.Add(URL);
    l:
        len_o = sublink.Count; len_o); 
        Console.WriteLine("-------------Level:" + counter++);
            for (int i = ini; i < len_o; i++) test(sublink[i].ToString());

        len_n = sublink.Count; 
        if (len_o < len_n) { ini = len_o; goto l; }

        Console.ReadKey();

        }
        //method to get the sub-links
        public static void test(string URL)
        {
            try
            {
                // Get HTML data 
                WebClient client = new WebClient();
                Stream data = client.OpenRead(URL);
                StreamReader reader = new StreamReader(data);

                string str = "", htmldata = "", temp;
                int n1, n2;
                str = reader.ReadLine();
                while (str != null)
                {
                    htmldata += str;
                    str = reader.ReadLine();

                }
                data.Close();
                    for (int i = 0; i < htmldata.Length - 5; i++)
                    {
                        if (htmldata.Substring(i, 5) == "href=")
                        {
                            n1 = htmldata.Substring(i + 6, htmldata.Length - (i + 6)).IndexOf("\"");
                            temp = htmldata.Substring(i + 6, n1);
                            if (temp.Length > 4 && temp.Substring(0, 4) != "http")
                            {   
                                if(temp.Substring(0,1)!="/")
                                temp=URL.Substring(0,URL.IndexOf(".com/")+5)+temp;
                                else temp = URL.Substring(0, URL.IndexOf(".com/") + 5) + temp.Remove(0,1);
                            }
                            if (temp.Length < 4) temp = URL.Substring(0, URL.IndexOf(".com/") + 5) + temp;
                            sublink.Add(temp);
                            n2 = htmldata.Substring(i + n1 + 1, htmldata.Length - (i + n1 + 1)).IndexOf("<");
                            subtitle.Add(htmldata.Substring(i + 6 + n1 + 2, n2 - 7));
                            i += tem开发者_开发知识库p.Length + htmldata.Substring(i + 6 + n1 + 2, n2 - 7).Length; 

                        }
                    }


                    for (int i = len_n; i < sublink.Count; i++) Console.WriteLine(i + "-->  " + sublink[i]);

            }
            catch (WebException exp)
            {
                Console.WriteLine("URL Could not be Resolved" + URL);
                Console.WriteLine(exp.Message, "Exception");
            }

        }
        } 

Why not using regular expressions? They are easier to read, debug and mantain. Also check out the Uri class. It has a couple of useful helpers (e.g. for base-relative url manipulation).

Also consider using an html/xml parser. There already was a discussion here. Parsing html as plain text (i.e. with regular expressions) seems to be easy at first, but it may soon become painful to add new features to your parser.