How to add characters to a string in C#

Question

Problem: I would like add characters to a phone.

So instead of displaying ###-###-####, I would like to display (###) ###-####.

I tried the foll

Answer 1

I would do something like this:

string FormatPhoneNumber(string phoneNumber)
{
    if (string.IsNullOrEmpty(phoneNumber))
        throw new ArgumentNullException(nameof(phoneNumber));

    var phoneParts = phoneNumber.Split('-');
    if (phoneParts.Length < 3)
        throw new ArgumentException("Something wrong with the input number format", nameof(phoneNumber));

    var firstChar = phoneParts[0].First();
    var lastChar = phoneParts[0].Last();
    if (firstChar == '(' && lastChar == ')')
        return phoneNumber;
    else if (firstChar == '(')
        return $"{phoneParts[0]})-{phoneParts[1]}-{phoneParts[2]}";
    else if (lastChar == ')') 
        return $"({phoneParts[0]}-{phoneParts[1]}-{phoneParts[2]}";

    return $"({phoneParts[0]})-{phoneParts[1]}-{phoneParts[2]}";
}

You would use it like this:

string n = "123-123-1234";
var formattedPhoneNumber = FormatPhoneNumber(n);