How to format a string as a telephone number in C#

Please note, this answer works with numeric data types (int, long). If you are starting with a string, you'll need to convert it to a number first. Also, please take into account that you'll need to validate that the initial string is at least 10 characters in length.

From a good page full of examples:

String.Format("{0:(###) ###-####}", 8005551212);

    This will output "(800) 555-1212".

Although a regex may work even better, keep in mind the old programming quote:

Some people, when confronted with a problem, think “I know, I’ll use regular expressions.” Now they have two problems.
--Jamie Zawinski, in comp.lang.emacs

I prefer to use regular expressions:

Regex.Replace("1112224444", @"(\d{3})(\d{3})(\d{4})", "$1-$2-$3");

You'll need to break it into substrings. While you could do that without any extra variables, it wouldn't be particularly nice. Here's one potential solution:

string phone = i["MyPhone"].ToString();
string area = phone.Substring(0, 3);
string major = phone.Substring(3, 3);
string minor = phone.Substring(6);
string formatted = string.Format("{0}-{1}-{2}", area, major, minor);

As far as I know you can't do this with string.Format ... you would have to handle this yourself. You could just strip out all non-numeric characters and then do something like:

string.Format("({0}) {1}-{2}",
     phoneNumber.Substring(0, 3),
     phoneNumber.Substring(3, 3),
     phoneNumber.Substring(6));

This assumes the data has been entered correctly, which you could use regular expressions to validate.

If you can get i["MyPhone"] as a long, you can use the long.ToString() method to format it:

Convert.ToLong(i["MyPhone"]).ToString("###-###-####");

See the MSDN page on Numeric Format Strings.

Be careful to use long rather than int: int could overflow.

        string phoneNum;
        string phoneFormat = "0#-###-###-####";
        phoneNum = Convert.ToInt64("011234567891").ToString(phoneFormat);

using string interpolation and the new array index/range

var p = "1234567890";
var formatted = $"({p[0..3]}) {p[3..6]}-{p[6..10]}"

Output: (123) 456-7890

Use Match in Regex to split, then output formatted string with match.groups

Regex regex = new Regex(@"(?<first3chr>\d{3})(?<next3chr>\d{3})(?<next4chr>\d{4})");
Match match = regex.Match(phone);
if (match.Success) return "(" + match.Groups["first3chr"].ToString() + ")" + " " + 
  match.Groups["next3chr"].ToString() + "-" + match.Groups["next4chr"].ToString();

Please use the following link for C# http://www.beansoftware.com/NET-Tutorials/format-string-phone-number.aspx

The easiest way to do format is using Regex.

private string FormatPhoneNumber(string phoneNum)
{
  string phoneFormat = "(###) ###-#### x####";

  Regex regexObj = new Regex(@"[^\d]");
  phoneNum = regexObj.Replace(phoneNum, "");
  if (phoneNum.Length > 0)
  {
    phoneNum = Convert.ToInt64(phoneNum).ToString(phoneFormat);
  }
  return phoneNum;
}

Pass your phoneNum as string 2021231234 up to 15 char.

FormatPhoneNumber(string phoneNum)

Another approach would be to use Substring

private string PhoneFormat(string phoneNum)
    {
      int max = 15, min = 10;
      string areaCode = phoneNum.Substring(0, 3);
      string mid = phoneNum.Substring(3, 3);
      string lastFour = phoneNum.Substring(6, 4);
      string extension = phoneNum.Substring(10, phoneNum.Length - min);
      if (phoneNum.Length == min)
      {
        return $"({areaCode}) {mid}-{lastFour}";
      }
      else if (phoneNum.Length > min && phoneNum.Length <= max)
      {
        return $"({areaCode}) {mid}-{lastFour} x{extension}";
      }
      return phoneNum;
    }

You can try {0: (000) 000-####} if your target number starts with 0.

Here is another way of doing it.

public string formatPhoneNumber(string _phoneNum)
{
    string phoneNum = _phoneNum;
    if (phoneNum == null)
        phoneNum = "";
    phoneNum = phoneNum.PadRight(10 - phoneNum.Length);
    phoneNum = phoneNum.Insert(0, "(").Insert(4,") ").Insert(9,"-");
    return phoneNum;
}

 Label12.Text = Convert.ToInt64(reader[6]).ToString("(###) ###-#### ");

This is my example! I hope can help you with this. regards

static void Main(string[] args)
    {
        Regex phonenumber = new(@"([0-9]{11})$");
        Console.WriteLine("Enter a Number: ");
        var number = Console.ReadLine();
        if(number.Length == 11)
        {
            if (phonenumber.IsMatch(number))
            {
                Console.WriteLine("Your Number is: "+number);
            }
            else
                Console.WriteLine("Nooob...");
        }
        else
            Console.WriteLine("Nooob...");
    }

Here is an improved version of @Jon Skeet answer with null checks and has a extension method.

public static string ToTelephoneNumberFormat(this string value, string format = "({0}) {1}-{2}") {
  if (string.IsNullOrWhiteSpace(value)) 
  {
    return value;
  } 
  else 
  {
    string area = value.Substring(0, 3) ?? "";
    string major = value.Substring(3, 3) ?? "";
    string minor = value.Substring(6) ?? "";
    return string.Format(format, area, major, minor);
  }
}