Анализ введеной на английском строки.

private readonly char[] _vowels = new char [] {'a', 'o', 'u', 'e', 'i', 'y'};
 
private void button1_Click(object sender, EventArgs e)
{
  string text = textBox1.Text;
  string [] words = text.Split(' ');
  var wordsData = new List<WordData>();
  foreach (var word in words){
    var wordData = new WordData() {Letters = 0, Vowels = 0, Consonants = 0, Others = 0, Word = word};
    for (int i = 0; i < word.Length; i++){
      if (char.IsLetter(word[i])){
    wordData.Letters++;
    if (_vowels.Contains(word[i]))
      wordData.Vowels++;
    else
      wordData.Consonants++;
      }
      else
    wordData.Others++;
    }
    wordsData.Add(wordData);
  }
  foreach (var wordData in wordsData)
    listBox1.Items.Add (string.Format("{0} : total {1} , vowels {2}, consonants {3}, others {4}", wordData.Word, wordData.Letters, wordData.Vowels, wordData.Consonants, wordData.Others));
  label1.Text = string.Format (" Words: {0} \r\n Av. Lenght = {1} \r\n Total Vowels = {2} \r\n Total Consonants = {3} ", 
      words.Length, words.Select(w=>w.Length).Average(), wordsData.Sum(w=>w.Vowels), wordsData.Sum(w=>w.Consonants));
}

struct WordData {
  public string Word;
  public int Letters;
  public int Vowels;
  public int Consonants;
  public int Others;
}