simple array to show data in page

protected void Page_Load(object sender, EventArgs e)
    {
        int len;        
        string[] a = new string[5];
        a[0] = "vikas";
        a[1] = "op";
        a[2] = "xas";
        a[3] = "cio";
        a[4] = "lol";
       string a1=Request.Querystring["xyz"];
       if (a1.Length > 0)
       {       
           foreach (string name in a)
           {             
               if(name.Contains(a1))
                   Response.Write(name+"<br/>");
              
           }
       }



string was not recognised as valid datetime error
    

   DateTime ValidDate = DateTime.Now;
        string format = "dd-MM-yyyy";
        CultureInfo provider = CultureInfo.InvariantCulture;
        DateTime.TryParseExact(DateTime.Now.ToString("dd-MM-yyyy"), format, null,      DateTimeStyles.None, out ValidDate);