public class Ch20_4_Exercise		// page 741
{
	public static void main(String[] args)
	{
		System.out.println("2^5 = " + twoToThePowerOf(5));
		System.out.println("2^16 = " + twoToThePowerOf(16));
		System.out.println("2^30 = " + twoToThePowerOf(30));
		System.out.println("2^0 = " + twoToThePowerOf(0));
		
		System.out.println("2^-5 = " + twoWithNegative(-5));
		System.out.println("2^5 = " + twoWithNegative(5));
	}
	
	public static int twoToThePowerOf(int n)
	{
		if(n>0) return 2*twoToThePowerOf(n-1);		// recursive case returns 2*powerOf(n-1)
		else return 1;								// base case is 0
	}
	
	public static double twoWithNegative(int n)		// what about computing 2^-n?  
	{												// notice the change to a double since we are dividing by 2 instead of multiplying by 2
		if(n>0) return 2.0*twoWithNegative(n-1);
		else if(n<0) return 1.0/2*twoWithNegative(n+1);
		else return 1.0;
	}
}