string[] str = { "3","y","34","QQ","41","adsf4","7","52"};

class Digit
 {
 private int _D;

 public int D
 {
  get { return _D; }
  set { _D = value; }
 }

 public Digit(int digit)
 {
  this._D = digit;
 }
 }

public static bool TryParse(string str, out Digit digit)
 {
  digit = null;

  if (string.IsNullOrEmpty(str))
  return false;

  int i;
  if (!int.TryParse(str, out i))
  return false;
  digit = new Digit(i);
  return true;
 }

 public override string ToString()
 {
  return _D.ToString();
 }

string[] str = { "3","y","34","QQ","41","adsf4","7","52"};

  var result = new List<Digit>();

  foreach (string s in str)
  {
  Digit d;
  if (Digit.TryParse(s, out d))
   result.Add(d);
  }

  foreach (Digit d in result)
  {
  Console.WriteLine(d.ToString());
  }