private void Button_Click(object sender, RoutedEventArgs e) { List <int> list = new List <int>() { 55, 200, 740, 76, 230, 482, 95 }; NumbersChecker nc = new NumbersChecker(); List <int> returnList = nc.CheckList(list); string nums = ""; foreach (int i in returnList) { nums = nums + i.ToString() + " "; } MessageBox.Show("Numbers greater than 80: " + nums); }