Counting number of occurrences of characters from array in string?

Question

I'm writing code to determine whether a password contains enough punctuation characters.

How do I count the number of occurrences of any characters from a set?

Something along these lines:

private const string nonAlphaNumericCharSet = "#*!?£$+-^<>[]~()&";
...
public static bool PasswordMeetsStrengthRequirements(string password)
{
    return password.Length >= MINIMUM_PASSWORD_LENGTH && password.NumberOfOccurences(nonAlphaNumericCharSet.ToCharArray()) >= MINIMUM_NONALPHANUMERIC_CHARS;
}

Bonus points for an elegant linq solution.

Answer 1

How do I count the number of occurences of any characters from a set?

var count = password.Count(nonAlphaNumericCharSet.Contains);

Answer 2

you can count like this

int count = "he!l!l!o".Split('!').Length - 1;

it will return 3.

Using linq

int count="he!l!l!o".Count(x => x == '!');

Answer 3

Here's an example:

private const string nonAlphaNumericCharSet = "#*!?£$+-^<>[]~()&";

public static bool PasswordMeetsStrengthRequirements(string password)
{
    return password.Count(x => nonAlphaNumericCharSet.Contains(x)) > 2 && password.Length > 1;
}

public static void Main()
{
    PasswordMeetsStrengthRequirements("Test").Dump();
    PasswordMeetsStrengthRequirements("Test#").Dump();
    PasswordMeetsStrengthRequirements("(Test#").Dump();
    PasswordMeetsStrengthRequirements("(Te[st#").Dump();
}

Answer 4

what about a RegExp

Regex rgx = new Regex(@"^(?=.*(\W.*){4,}).{8,}$", RegexOptions.Compiled);
bool validPassword = rgx.IsMatch(password);

4=min not word/digit char

8= min password leght

Linq may be considered elegant (it isn't IMHO) but at which performance cost?

------------Update after comment---------------

if you want to match a subset of chars you have to replace \W with []

[]= range of chars

some chars have to be escaped with \

in your case: [#\*!\?£\$\+-\^\<\>\[\]~\(\)&]

there you can find a regular expression cheat sheet