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

using System;

public class Program
{
    public static void Main()
    {
        Console.WriteLine(AlphaPhoneToNumber("555-GET-FOOD"));
    }

    public static string AlphaPhoneToNumber(string val){
        //strings are immutable so let's get the array version of the value
        var phoneNumberArr = val.ToCharArray();
        for(int i = 0; i < val.Length; i++){
            phoneNumberArr[i] = AlphaPhoneCharToNumber(phoneNumberArr[i]);
        }
        return new string(phoneNumberArr);
    }

    public static char AlphaPhoneCharToNumber(char val){
        switch(val){
            case 'A':
            case 'B':
            case 'C':
                return '2';
            case 'D':
            case 'E':
            case 'F':
                return '3';
            case 'G':
            case 'H':
            case 'I':
                return '4';
            case 'J':
            case 'K':
            case 'L':
                return '5';
            case 'M':
            case 'N':
            case 'O':
                return '6';
            case 'P':
            case 'Q':
            case 'R':
                return '7';
            case 'S':
            case 'T':
            case 'U':
                return '8';
            case 'V':
            case 'W':
            case 'X':
            case 'Y':
            case 'Z':
                return '9';
            default: return val;

        }
    }
}

and here's how to do it without switch:

public static char AlphaPhoneCharToNumber2(char val){
    // All three arrays are of exact same length
    var ualphas = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
    var lalphas = "abcdefghijklmnopqrstuvwxyz".ToCharArray();
    var numval =  "22233344455566677788899999".ToCharArray();
    // thus I will loop up to the max length of one of the arrays
    // remember they are all the same length
    for(int i = 0; i < ualphas.Length; i++){
        //I will check if the value is in one of the alphabet
        //arrays at the current index
        //if there is a match I will assign it the number value
        //at the same index
        // MATCH UPPER?         MATCH LOWER?              RETURN NUMBER
        if(ualphas[i] == val || lalphas[i] == val) return numval[i];
    }
    // ELSE RETURN THE ORIGINAL VALUE
    return val;
}