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] = AlphaPhoneCharToNumber2(phoneNumberArr[i]);

        }

        return new string(phoneNumberArr);

    }

    public static char AlphaPhoneCharToNumber2(char val){

        var ualphas = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();

        var lalphas = "abcdefghijklmnopqrstuvwxyz".ToCharArray();

        var numval = "22233344455566677788899999".ToCharArray();

        for(int i = 0; i < ualphas.Length; i++){

            if(ualphas[i] == val || lalphas[i] == val) return numval[i];

        }

        return val;

    }

    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;

​

        }

    }

}