ScanAndSwitch.java

import java.util.*; // for scanner

public class ScanAndSwitch {

    /**
    *   Program:    ScanAndSwitch.java
    *   Purpose:    Yahoo! Answers question
    *   Creator:    Chris Clarke, author "50 Java Program Source Codes" e-book
    *   Created:    29.10.2013
    */

    public static void main(String[] args) {

        // create scanner
        Scanner scan = new Scanner(System.in);

        // variables will contain input numbers
        int x = 0, y = 0;

        // maths operator character which will be input
        char m = ' ';

        // the letter as input string
        String let = "";

        int result = 0; // the result of the mathematical operation
        String op = ""; // the operator (+, * or %)

        // boolean error flag
        boolean letterError;

        try {
            // prompt for input
            System.out.print("Enter integer value for x: ");
            // read integer from keyboard
            x = scan.nextInt();

            // prompt for input
            System.out.print("Enter integer value for y: ");
            // read integer from keyboard
            y = scan.nextInt();

        } catch (InputMismatchException e) {
            //e.printStackTrace();
            System.out.println("That\'s not an integer!");
            System.exit(1);
        } // end try/catch

        do { // start do/while loop
            // set error flag to false
            letterError = false;
            // prompt for a letter
            System.out.print("Enter a, b or c: ");
            // read letter as string from keyboard
            let = scan.next();
            // convert to lower case
            let = let.toLowerCase();
            // get first character
            m = let.charAt(0);

            // branch according to m
            switch (m) {
                case 'a': result = x + y; op = " + "; break;
                case 'b': result = x * y; op = " * "; break;
                case 'c': if (y != 0) { // if y isn't zero
                        result = x % y; op = " % "; break;
                      } else { // y was zero
                        System.out.println("Modulo zero error!");
                        // end program
                        System.exit(1);
                      } // end if
                default : System.out.println("Invalid letter, try again.");
                      // set error flag to true
                      letterError = true;
            } // end switch
        } while (letterError); // end do/while loop

        // output result
        System.out.println(x + op + y + " = " + result);

    } // end main()

} // end class