// Java implementation of some scheme programs from CSI
// Written by the MCS-178 gang
// March 20, 2006

class AnythingButHelloWorld {
  public static void main(String[] args)
  {
    System.out.println("\nTesting factorial()");
    for (int i = 0; i < 10; i++)
    {
      System.out.println(i + "! = " + factorial(i));
    }

    System.out.print("\nThe sum from 1 to 10 is ");
    System.out.println(sumFromTo(1, 10));

    System.out.print("\nThe number of digits in -380000000 is ");
    System.out.println(numberOfDigits(-380000000));

    System.out.println("\nTesting factorialIteratively()");
    for (int i = 0; i < 10; i++)
    {
      System.out.println(i + "! = " + factorialIteratively(i));
    }

    System.out.print("\nIs 6 perfect? ");
    System.out.println(isPerfect(6));
    System.out.print("Is 7 perfect? ");
    System.out.println(isPerfect(7));
    System.out.println();
  }

  public static int factorial(int n) {
    if (n == 0) {
      return 1;
    } else {
      return n * factorial(n-1);
    }
  }

  public static int sumFromTo(int lower, int upper)
  {
    int sum = 0;
    for (int i = lower; i <= upper; i++)
    {
      sum += i;
    }
    return sum;
  }
  
  public static int numberOfDigits(int number)
  {
    if (number < 0)
    {
      return numberOfDigits(0 - number);
    }
    else if (number < 10)
    {
      return 1;
    }
    else
    {
      return (1 + numberOfDigits(number / 10));
    }
  }

  public static int factorialIteratively(int n)
  {
    int value = 1;
    int i = 1;
    while (i <= n)
    {
      value *= i;
      i++;
    }
    return value;
  }

  public static boolean isPerfect(int n)
  {
  /*
    if (sumOfDivisors(n) == (2 * n))
      return true;
    else
      return false;
  */
    return (sumOfDivisors(n) == (2 * n));
  }

  public static int sumOfDivisors(int n)
  {
    int value = 0;
    int i = n;
    while  (i >= 1)
    {
      if ((n % i) == 0)
        value += i;
      i--;  
    }
    return value;
  }
}