private void buttonAnalysis_Click(object sender, EventArgs e)
        {
            string text = textBox.Text;
            Dictionary<char, int> result = new Dictionary<char, int>();

            foreach (var ch in chars)
            {
                int count = 0;

                for (int i = 0; i < textBox.Text.Length; i++)
                {
                    if (text[i] == ch || text[i] == Char.ToUpper(ch))
                        count++;
                }
                result.Add(ch, count);
            }

            var sortedDict = from entry in result orderby entry.Key ascending select entry;

            textBoxOut.Clear();

            foreach (KeyValuePair<char, int> item in sortedDict)
            {
                if(item.Value != 0)
                    textBoxOut.AppendText(Char.ToUpper(item.Key) + ": " + item.Value + "\r\n");
            }
        }