CountAccents.cs

void CountAccents(string input)
{
    if (input.Length != 0 && !Char.IsWhiteSpace(input[input.Length - 1])) input = input + " ";
	int wordsTotal = 0;
	int wordsOnlyLetters = 0;
	int wordsAccented = 0;
	
	int wordStart = 0;
	bool hasAccent = false;
	bool hasNonLetter = false;
	for (int i = 0; i < input.Length; ++i)
	{
		var c = input[i];
		if (Char.IsWhiteSpace(c) || Char.IsSeparator(c) || Char.IsPunctuation(c))
		{
			int wordLength = i - wordStart;
			if (wordLength > 0)
			{
				++wordsTotal;
				if (!hasNonLetter && wordLength > 0) ++wordsOnlyLetters;
				if (!hasNonLetter && wordLength > 0 && hasAccent) ++wordsAccented;
			}
			wordStart = i + 1;
			hasNonLetter = hasAccent = false;
		}
		else if (!Char.IsLetter(c))
		{
			hasNonLetter = true;
		}
		else if (c > '\u0080')
		{
			hasAccent = true;
		}
	}
	
	Console.WriteLine("{0} words total, {1} real words, {2} ({3:N1} %) with accents", wordsTotal, wordsOnlyLetters, wordsAccented, 100.0 * wordsAccented / wordsOnlyLetters);
}