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Iterative/recursive methods

Iterative/recursive methods

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Program1	15 Oct, 2008 - 08:22 AM Post #1
New D.I.C Head Joined: 25 Apr, 2008 Posts: 11 My Contributions	I need to write an iterative method called power1 to compute x^n for some n>=0. This is all I have so far. Any help is appreciated CODE import java.awt.; import javax.swing.; import java.lang.Math.*; class power1 { power1() { int n=0; int x=0; while (n<0) { x = x^n; } System.out.println(); } }
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Locke37	RE: Iterative/recursive Methods 15 Oct, 2008 - 08:40 AM Post #2
I'm not a thief...I prefer the term TREASURE HUNTER! Joined: 20 Mar, 2008 Posts: 1,005 Thanked: 39 times Dream Kudos: 325 My Contributions	The operator ^ will not do what you want it to do. It's a bitwise operator, not a power operator. Try this. java public static double power(int base, int exp) { double answer = base; for (int x = exp; x > 0; x--) { // code to multiply stuff here } } I'm not going to give you the entire method, but this will loop exp - 1 number of times passed to the method by exp. You should multiply something by something else in that loop. It takes only 1 statement if I'm thinking correctly (I'm in a music class, so I'm a little distracted ) Hope this helps! This post has been edited by Locke37: 15 Oct, 2008 - 08:41 AM
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Program1	RE: Iterative/recursive Methods 15 Oct, 2008 - 08:43 AM Post #3
New D.I.C Head Joined: 25 Apr, 2008 Posts: 11 My Contributions	QUOTE(Locke37 @ 15 Oct, 2008 - 09:40 AM) The operator ^ will not do what you want it to do. It's a bitwise operator, not a power operator. Try this. java public static double power(int base, int exp) { double answer = base; for (int x = exp; x > 0; x--) { // code to multiply stuff here } } I'm not going to give you the entire method, but this will loop exp - 1 number of times passed to the method by exp. You should multiply something by something else in that loop. It takes only 1 statement if I'm thinking correctly (I'm in a music class, so I'm a little distracted ) Hope this helps! Thanks. I'll try it your way.
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bbq

RE: Iterative/recursive Methods
15 Oct, 2008 - 08:44 AM

Post #4

D.I.C Head

Joined: 15 May, 2008
Posts: 192

Linux

Thanked: 17 times
Dream Kudos: 50
My Contributions

This works, i just coded it up. You could use integers however i prefer using doubles and perhaps a string format if you are to print the values out...

Function

java


double determinePower(double base, double power)
	{
		double answer = 1;		

		if (power == 0)
		return 1;
		
		else if (power == 1)		
		return base;

		else
		for(int i = 1; i <= power; i++)
		{
			answer *= base;
		}
		return answer;
		

	}

Full example implementation

java


class Power
{
	void run()
	{
		System.out.println("Program to compute a number a to the power of b\nTrial Values will be 5^0, 5^1 and 5^2, 5^3\nEnjoy");
		
		System.out.println(String.format("%.0f",determinePower(5,0)) ); 
		System.out.println(String.format("%.0f",determinePower(5,1)) );
		System.out.println(String.format("%.0f",determinePower(5,2)) );
		System.out.println(String.format("%.0f",determinePower(5,3)) );
	}
	
	double determinePower(double base, double power)
	{
		double answer = 1;		

		if (power == 0)
		return 1;
		
		else if (power == 1)		
		return base;

		else
		for(int i = 1; i <= power; i++)
		{
			answer *= base;
		}
		return answer;
		

	}

	public static void main(String[] args)
	{
		Power myPower = new Power();
		myPower.run();
	}


}

Hope this helped you

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Program1

RE: Iterative/recursive Methods
15 Oct, 2008 - 08:53 AM

Post #5

New D.I.C Head

Joined: 25 Apr, 2008
Posts: 11

Windows

My Contributions

QUOTE(bbq @ 15 Oct, 2008 - 09:44 AM)

This works, i just coded it up. You could use integers however i prefer using doubles and perhaps a string format if you are to print the values out...

Function

java


double determinePower(double base, double power)
	{
		double answer = 1;		

		if (power == 0)
		return 1;
		
		else if (power == 1)		
		return base;

		else
		for(int i = 1; i <= power; i++)
		{
			answer *= base;
		}
		return answer;
		

	}

Full example implementation

java


class Power
{
	void run()
	{
		System.out.println("Program to compute a number a to the power of b\nTrial Values will be 5^0, 5^1 and 5^2, 5^3\nEnjoy");
		
		System.out.println(String.format("%.0f",determinePower(5,0)) ); 
		System.out.println(String.format("%.0f",determinePower(5,1)) );
		System.out.println(String.format("%.0f",determinePower(5,2)) );
		System.out.println(String.format("%.0f",determinePower(5,3)) );
	}
	
	double determinePower(double base, double power)
	{
		double answer = 1;		

		if (power == 0)
		return 1;
		
		else if (power == 1)		
		return base;

		else
		for(int i = 1; i <= power; i++)
		{
			answer *= base;
		}
		return answer;
		

	}

	public static void main(String[] args)
	{
		Power myPower = new Power();
		myPower.run();
	}


}

Hope this helped you

Yes, this helps a lot. Thank you very much.

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bbq	RE: Iterative/recursive Methods 21 Oct, 2008 - 11:26 PM Post #6
D.I.C Head Joined: 15 May, 2008 Posts: 192 Thanked: 17 times Dream Kudos: 50 My Contributions	You are welcome
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Gloin	RE: Iterative/recursive Methods 22 Oct, 2008 - 02:28 AM Post #7
On MeD.i.Cation Joined: 4 Aug, 2008 Posts: 723 Thanked: 47 times My Contributions	This topic has been discussed before and it should be added that the function can be written recursively to perform in logarithmic time which is (for large powers) a substantial improvement to the iterative version that performs in linear time. ex: To calculate x^1000 using the iterative version will need to do 1000 multiplications. To calculate x^1000 using the recursive version will need to do 2log(1000) = 10 multiplications. (This is not equivalent with recursion being 100 times faster since handling of registers will take different time depending on the size of the numbers. Needless to say it's still alot faster)
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