Exercise 15: Count

A program is needed which prints a number out in words. To make the program manageable, it only needs to print out numbers which use the digits 0, 1, 2 and it only needs to handle numbers up to three digits long. The program has already been divided into several functions. Some of these, including the most difficult one digits, have been written for you. Your job is to fill in the details of the last few functions.

// Print a number in words.  The number can be up to three digits long, and
// must only use the digits 0, 1, 2.

class Count
{
   public static void main(String[] args)
   {
      Count program = new Count();
      if (args.length != 1)
      {
         System.err.println("Usage: java Count n");
         System.exit(1);
      }
      program.print(args[0]);
   }

// Print a number, given as a string, in words.
   void print(String s)
   {
      int n = Integer.parseInt(s);
      String result = convert (n);
      System.out.println(result);
   }

// Convert a number into words
   String convert(int n)
   {
      int h = n / 100;
      int t = (n / 10) % 10;
      int u = n % 10;
      String result = digits(h, t, u);
      return result;
   }

// Convert a number given as three digits into words.
   String digits(int h, int t, int u)
   {
      String s = "";
      if (h > 0)
      {
         s = hundreds(h);
         if (t > 0 || u > 0) s = s + " and ";
      }
      if (t == 1 && u > 0) s = s + teens(10 + u);
      else
      {
         if (t > 0)
         {
            s = s + tens(t);
            if (u > 0) s = s + " ";
         }
         if (u > 0 || (h == 0 && t == 0))
         {
            s = s + units(u);
         }
      }
      return s;
   }

// Convert a number h of hundreds into a phrase, where 0 < h <= 2.
   String hundreds(int h)
   {
      return "one hundred";
   }

// Convert a number t of tens into a word, where 0 < t <= 2.
   String tens(int t)
   {
      return "ten";
   }

// Convert a number n into a word, where 10 < n <= 12.
   String teens(int n)
   {
      return "eleven";
   }

// Convert a single-digit number u into a word, where 0 <= u <= 2.
   String units(int u)
   {
      return "zero";
   }
}

Hint

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