Write a function that returns the digit value (an integer) corresponding to the letter passed to it an argument based on the encoding on your telephone handset. for example, if the argument is the letter a, b, or c (uppercase or lowercase), your function should return the digit 2. if the argument is not one of the letters of the alphabet, return a value of -1. implement two versions of the function: one using a switch statement and one using a nested if statement. provide a program which tests each function (you may provide two separate source code files or combine them in one source code file which gives you the choice of which function to run).