Count occurrences of a character

Because of the reasons explained in Remarks section you can’t simply do this (unless you want to count occurrences of a specific code-unit):

int count = text.Count(x => x == ch);

You need a more complex function:

public static int CountOccurrencesOf(this string text, string character)
{
    return text.EnumerateCharacters()
        .Count(x => String.Equals(x, character, StringComparer.CurrentCulture));
}

Note that string comparison (in contrast to character comparison which is culture invariant) must always be performed according to rules to a specific culture.