c# Alpha Telephone Number Translator

Question

I have a homework assignment where the program will accept any phone number in the format similar to 555-GET-FOOD. The task is to map the alphabetic letters to numbers and tran

Answer 1

Here are some options for simple logic to process phone numbers as described. Note that while a novel approach, using an Enum to map letters to integer values somewhat complicates the process more than it needed to be.

Even though other methods exist for specifically mapping alpha-numeric phone numbers (think Regex) if you do ever need to iterate or process using Enum Names and Values then I hope you find these algorithms useful.

A dictionary would have been far simpler as a mapping construct to process from.

Regex where the LetterNumber mapping is defined in the expression would have been superior again.

/// 

/// Iterates through the characters in a phone number converting letters to digits.
/// 
/// Uses StringBuilder to build the output iteratively, this method does not attempt to validate the number passed in
/// 
/// Phone number to parse
/// Phone number output where letters have been parsed into their digit values
private string ParsePhoneNumber_StringBuilder(string str)
{
    StringBuilder output = new StringBuilder();
    foreach (char ch in str.ToCharArray())
    {
        // Convert each letter to it's numeric value as defined in the LetterNumber enum
        // Dashes are not letters so they will get passed through
        if (char.IsLetter(ch))
        {
            if (Enum.IsDefined(typeof(LetterNumber), ch.ToString()))
            {
                LetterNumber letterNumber = (LetterNumber)Enum.Parse(typeof(LetterNumber), ch.ToString(), true);
                output.Append((int)letterNumber);
            }
        }
        else
            output.Append(ch);
    }
    return output.ToString();
}

/// 

/// Uses Linq to parse the characters in a phone number converting letters to digits.
/// 
/// This method does not attempt to validate the number passed in
/// 
/// Phone number to parse
/// Phone number output where letters have been parsed into their digit values
private string ParsePhoneNumber_Linq(string str)
{
    return String.Join("", str.Select(c => char.IsLetter(c) ? ((int)((LetterNumber)Enum.Parse(typeof(LetterNumber), c.ToString(), true))).ToString() : c.ToString()));
}

/// 

/// Iterates through the LetterNumber values and replaces values found in the passed in phone number.
/// 
/// Iterates through Enum Names and applied String.Replace
/// 
/// Phone number to parse
/// Phone number output where letters have been parsed into their digit values
private string ParsePhoneNumber_Replacement(string str)
{
    str = str.ToUpper(); // we will compare all letters in upper case
    foreach (string letter in Enum.GetNames(typeof(LetterNumber)))
        str = str.Replace(letter.ToUpper(), ((int)((LetterNumber)Enum.Parse(typeof(LetterNumber), letter))).ToString());
    return str;
}