/**
 * Calculates and displays the result of x to y power for two integers entered on the command line.
 * Both Iterative and Recursive methods are used.
 * 
 * @author William McDaniel Albritton
 */
public class Powers {

  /**
   * Program starts here
   * 
   * @param commandlineArguments The 1st and 2nd commandline argument should be a non-negative
   *        number
   */
  public static void main(String[] commandlineArguments) {
    // check for correct number of commandlineArguments (at least 2)
    if (commandlineArguments.length <= 1) {
      System.out.print("Error: You must enter at least 2 commandline arguments!");
    }
    else {
      // initialize variables
      Integer x = new Integer(0);
      Integer y = new Integer(0);
      // error checking to see if it is an integer
      try {
        x = Integer.parseInt(commandlineArguments[0]);
      }
      catch (NumberFormatException exception) {
        System.out.print(exception);
        System.out.println(" is not an integer!");
        System.exit(1); // end program
      }
      // error checking to see if it is an integer
      try {
        y = Integer.parseInt(commandlineArguments[1]);
      }
      catch (NumberFormatException exception) {
        System.out.print(exception);
        System.out.println(" is not an integer!");
        System.exit(1); // end program
      }
      // call iterative method
      Integer result = Powers.iterative(x, y); // A (return address)
      // error checking to see if it is non-negative
      if (result.equals(-1)) {
        System.out.println("ERROR: Negative integers are undefined for this power function!");
      }
      else {
        System.out.println(x + "^" + y + " = " + result);
      }
      // call recursive method
      result = Powers.recursive(x, y); // B (return address)
      // error checking to see if it is non-negative
      if (result.equals(-1)) {
        System.out.println("ERROR: Negative integers are undefined for this power function!");
      }
      else {
        System.out.println(x + "^" + y + " = " + result);
      }
    }
  }// end of main

  /**
   * Computes the power of a nonnegative numbers with iteration (loops)
   * 
   * @param x is a nonnegative integer (base)
   * @param y is a nonnegative integer (exponent)
   * @return the result of x to the power of y (x^y), or -1 for negative integers (error)
   */
  public static Integer iterative(Integer x, Integer y) {
    // check for negative integers
    if (x < 0 || y < 0) {
      return -1; // error condition
    }
    // by mathematical definition, x^0 = 1
    if (y.equals(0)) {
      return 1;
    }
    // need to use integer variable to store product
    Integer product = new Integer(1);
    // loop from 1 to y, count up by 1
    for (int i = 1; i <= y; i++) {
      // multiply x, y times to get power result
      product = product * x;
    }
    // return result of power
    return product;
  }// end of iterative

  /**
   * Computes the power of a nonnegative numbers with recursion
   * 
   * @param x is a nonnegative integer (base)
   * @param y is a nonnegative integer (exponent)
   * @return the result of x to the power of y (x^y), or -1 for negative integers (error)
   */
  public static Integer recursive(Integer x, Integer y) {
    // base case #1: check for negative integers
    if (x < 0 || y < 0) {
      return -1; // error condition
    }
    // base case #2: by mathematical definition, x^0 = 1
    if (y.equals(0)) {
      return 1;
    }
    // recursive case: return x * (method call for y-1)
    // we must make the problem smaller by subtracting one!
    return x * Powers.recursive(x, y - 1); // C (return address)
  }// end of recursive

}// end of class