Regex Numeric Pattern and Exclude Pattern

To remove non numeric characters from alpha numeric string by using Regex, to do this we can use regular expressions, have a look at below code snippet.

Regex exculdePattern = new Regex(@"[^.0-9]", RegexOptions.Compiled);
if (exculdePattern.IsMatch(phoneNumber))
{
    phoneNumber = exculdePattern.Replace(phoneNumber, string.Empty);
}

If the phone number is alpha numeric, the above code snippet replaces all non numeric characters with empty. 

The below pattern removes a specific character i.e. hyphen(-).

Regex exculdePattern = new Regex(@"[-]+", RegexOptions.Compiled);

To verify the phone number is a numeric and minumum length, the below numeric pattern helps.

Regex numericPattern = new Regex(@"\d{10}$", RegexOptions.Compiled);
if (numericPattern.IsMatch(phoneNumber))
{
    double phoneNum = Convert.ToDouble(phoneNumber);
    Console.Write("\n"+phoneNum.ToString("(###) ###-####"));
    phoneNumber = string.Concat(phoneNumber.Substring(0, 3), "-", 

phoneNumber.Substring(3, 3), "-", phoneNumber.Substring(6, 4));
    Console.Write("\n" + phoneNumber);
}