Best way to convert Pascal Case to a sentence

Question

What is the best way to convert from Pascal Case (upper Camel Case) to a sentence.

For example starting with

\"AwaitingFeedback\"

a

Answer 1

Most of the preceding answers split acronyms and numbers, adding a space in front of each character. I wanted acronyms and numbers to be kept together so I have a simple state machine that emits a space every time the input transitions from one state to the other.

    /// 

    /// Add a space before any capitalized letter (but not for a run of capitals or numbers)
    /// 
    internal static string FromCamelCaseToSentence(string input)
    {
        if (string.IsNullOrEmpty(input)) return String.Empty;

        var sb = new StringBuilder();
        bool upper = true;

        for (var i = 0; i < input.Length; i++)
        {
            bool isUpperOrDigit = char.IsUpper(input[i]) || char.IsDigit(input[i]);
            // any time we transition to upper or digits, it's a new word
            if (!upper && isUpperOrDigit)
            {
                sb.Append(' ');
            }
            sb.Append(input[i]);
            upper = isUpperOrDigit;
        }

        return sb.ToString();
    }

And here's some tests:

    [TestCase(null, ExpectedResult = "")]
    [TestCase("", ExpectedResult = "")]
    [TestCase("ABC", ExpectedResult = "ABC")]
    [TestCase("abc", ExpectedResult = "abc")]
    [TestCase("camelCase", ExpectedResult = "camel Case")]
    [TestCase("PascalCase", ExpectedResult = "Pascal Case")]
    [TestCase("Pascal123", ExpectedResult = "Pascal 123")]
    [TestCase("CustomerID", ExpectedResult = "Customer ID")]
    [TestCase("CustomABC123", ExpectedResult = "Custom ABC123")]
    public string CanSplitCamelCase(string input)
    {
        return FromCamelCaseToSentence(input);
    }