Telephone number validation

Question

I have this code to validate a phone number but it looks a bit awkward. I'm guessing theres a better way to go about this. How can I make this more efficient?

public static bool validTelephoneNo(string telNo)
{
    bool condition = false;
    while (condition == false)
    {
        Console.WriteLine("Enter a phone number.");
        telNo = Console.ReadLine();
        if (telNo.Length > 8)
        {
            if (telNo.StartsWith("+") == true)
            {
                char[] arr = telNo.ToCharArray();
                for (int a = 1; a < telNo.Length; a++)
                {
                    int temp;

                    try
                    {
                        temp = arr[a];
                    }

                    catch
                    {
                        break;
                    }

                    if (a == telNo.Length - 1)
                    {
                        condition = true;
                    }
                }
            }
        }
    }
    return true;
}

consists of integers, is less than 8 digits in length and has a plus at the start — Adam Higgins, Apr 29 '15 at 10:29
what is the valid format of telefone number? Use Regular expression. — Jack, Apr 29 '15 at 10:30
Refer : http://stackoverflow.com/questions/18091324/regex-to-match-all-us-phone-number-formats — captainsac, Apr 29 '15 at 10:32
This code doesn't appear to work. There is no possible way to return `false`. All phone numbers will be validated, right? If this is the case, this question *would not* be a good fit for [codereview.se], @SonerGönül Code that does not work is off-topic for [codereview.se]. — nhgrif, Apr 29 '15 at 10:33
possible duplicate of [Basic Regular Expression for a 'generic' phone number](http://stackoverflow.com/questions/6330399/basic-regular-expression-for-a-generic-phone-number) — Fenton, Apr 29 '15 at 10:34
I think its more than 8 characters will also work Check that if condition inside loop — captainsac, Apr 29 '15 at 10:34

Richard · Answer 1 · 2015-04-29T11:31:07.380

6

Don't try and do this yourself, use a library where someone has already done the hard work for you, such as libphonenumber.

Example:

public static bool validTelephoneNo(string telNo)
{
    PhoneNumber number;
    try
    {
        number = PhoneNumberUtil.Instance.Parse(telNo, "US");  // Change to your default language, international numbers will still be recognised.
    }
    catch (NumberParseException e)
    {
        return false;
    }

    return number.IsValidNumber;
}

This library will handle parsing and formatting phone numbers from different countries. Not only will this ensure that the number is valid in the relevant country, it will also allow you to filter out premium numbers and "fake" numbers (such as 555 in the US).

edited Apr 29 '15 at 11:31

answered Apr 29 '15 at 11:25

Richard

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Hi @Richard, I want to use the libphonenumber library in a c# plugin for dynamics. However, using MSILMerge this doesn't seem to work, since it's a weakly signed assembly. I also tried using BrutalDev Strong signer to get around the weak signing. But, then I get the error "Could not find reference: PhoneNumbers, ..." Any clue how to make this work? – Tim Hage Jun 22 '22 at 13:08
I made another thread around this, hopefully you can help me out on this one https://stackoverflow.com/questions/71321559/how-to-use-google-lib-phonenumbers-in-dynamics-c-sharp-plugin – Tim Hage Jun 22 '22 at 13:09

score 5 · Accepted Answer · answered Apr 29 '15 at 10:33

Your goal can be easily achieved using regular expressions:

public static bool validTelephoneNo(string telNo)
{
    return Regex.Match(telNo, @"^\+\d{1,7}$").Success;
}

This pattern is exactly as stated: consists of integers, is less than 8 digits in length and has a plus at the start, and also this pattern can be modified if conditions somehow more complex.

score 3 · Answer 3 · edited Apr 29 '15 at 11:20

3

try

Console.WriteLine("Enter a phone number.");
bool isValid = new System.Text.RegularExpressions.Regex(@"^[+]\d{1,7}$").IsMatch(Console.ReadLine());

Where the regex checks whether there is only a single number (1 to 7 digits) with + in front of them read. The drawback, this way you cannot further processed, you might need to read the line from console to a new variable.

edited Apr 29 '15 at 11:20

Gábor Bakos

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answered Apr 29 '15 at 10:33

fubo

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Telephone number validation

3 Answers3