protected void Count(object sender, EventArgs e)
    {
        string test = "Vasanth";
        List<string> str = new List<string>();
        char[] chrs = test.ToCharArray(); 
        for (int i = 0; i < chrs.Length; i++) {
            var s = chrs[i] + " " + Occurence(test, chrs[i]);
            if (str.IndexOf(s) == -1)
            {
                str.Add(s);
            }
        } 
        Label1.Text = string.Join("<br />", str);
    }

    private int Occurence(string text, char chr)
    {
        int i = 0, count = 0;
        while ((i = text.IndexOf(chr, i)) != -1)
        {
            count++;
            i++;
        }
        return count;
    }