/* Java class that includes a method that translates a given integer
** numeral (i.e., a String composed of decimal digit characters) into
** the corresponding integer value.  (In other words, the method
** re-implements the Integer.parseInt() method found in Java's standard
** library.)  The point is to illustrate the development of a loop that
** conforms to a proposed loop invariant.
**
** Authors: R. McCloskey and < STUDENTS' NAMES >
*/
public class Numeral2Number {

   /* Returns the integer value described by the given numeral, which
   ** is assumed to be a sequence of decimal digits.
   ** Example: The numeral "5834" yields the int value 5834
   ** pre: Letting N = numeral.length():
   **      N > 0 and
   **      for all i in [0..N), numeral.charAt(i) is one of '0', '1', ..., '9'.
   ** post: value returned is Integer.parseInt(numeral)
   */
   public static int numeralToNumber(String numeral) {
      // Introduce local variable N as a convenient shorthand.
      final int N = numeral.length();
      int result = digitToNum(numeral.charAt(0));
      int i = 1;
      // pre-loop loop invariant check:
      assert result == Integer.parseInt(numeral.substring(0,i));
      while (i != N) {
         result = ??;
         i = i+1;
         // Verify loop invariant at end of each iteration:
         assert result == Integer.parseInt(numeral.substring(0,i));
      }
      assert result == Integer.parseInt(numeral);
      return result;
   }
   //Note: The loop invariant says that the value of 'result' is the
   //      number represented by the prefix of length i of 'numeral'


   /* Given a digit character (i.e., one of '0', '1', '2', ..., '9'), 
   ** returns the corresponding numeric value (of type int).
   */
   private static int digitToNum(char digit) { return digit - '0'; }


   /* This method expects to receive a single argument that is a
   ** decimal integer numeral (meaning a string of digit characters,
   ** like "80345").  It calls the numeralToNumber() method to compute 
   ** the corresponding integer value and reports the results.
   */
   public static void main(String[] args) {
      String theNumeral = args[0];

      // Call numeralToNumber() to compute the number described by
      // the given numeral and report the result.
      int number = numeralToNumber(theNumeral);

      System.out.printf("The integer represented by numeral \"%s\" is %d\n",
                        theNumeral, number);
   }

}