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question on iteration

Ricky James
Ranch Hand

Joined: Mar 26, 2007
Posts: 83
Hello,

I am practicing iteration from a book and it has the following ex:

The greatest common factor (GCF) of two numbers is the largest number that evenly divides both numbers. Using Euclid�s method, create two codes for computing the GCF of two numbers. Use iteration for the first code and recursion for the other one.
Notes on Euclid�s algorithm:
1. Get input integers x and y.
2. Repeat the following step while y != 0
a. y = x % y;
b. x = old value of y
3. Return x.
For example, x = 14 and y = 6.
y = x % y = 14 % 6 = 2
x = 6
y = x % y = 6 % 2 = 0
x = 2 (GCF)

I tried this code with iteration and I am pasting it here:

public class ExerciseOne {

static int GCF(int x, int y){
while (y != 0){
y = x % y;
x = y;
}
return x;
}

public static void main(String args[]){
System.out.println(GCF(14,6));
}
}

-----------------------------------------------------

Now I know the answer to this exercise is 2 and I am doing something fundamentally wrong. Can anyone please point out what is the problem with my code?

I can see that x doesn't get the 'old value' of y. But I don't know how I can do it.

Shall be extremely grateful.
Thanks
Ricky
Shashi Kant
Ranch Hand

Joined: Aug 08, 2006
Posts: 117
Hello Ricky

In your code


you are assigning the value of y to x after changing the orginal value of y
i.e.

So modify your code like
By this you will get the old value of y.

Regards
Shashikant


If it's true that we are here to help others, then what exactly are the others here for?
Ricky James
Ranch Hand

Joined: Mar 26, 2007
Posts: 83
Hello Shashikant,

Thanks for the reply. I tried what you advised but even that gives me an error.

When I assign the value of y into x before the statement y = x % y I get the answer 6 which is the value of y so that means that the new value never gets assigned, and x takes the original value of y.

Ricky
Shashi Kant
Ranch Hand

Joined: Aug 08, 2006
Posts: 117
Hello Ricky

Instead of returning the value of x why can't you return value of y directly.

Regards
Shashikant
Ricky James
Ranch Hand

Joined: Mar 26, 2007
Posts: 83
Originally posted by Shashikant Dahatonde:
Hello Ricky

Instead of returning the value of x why can't you return value of y directly.

Regards
Shashikant



Hi Shashikant,

I am trying to follow the requirements of the exercise. And they state the pseudocode that is to be followed.

I know this can be done using recursion as well and that is the next step of the exercise. But first I want to do the way the exercise suggests.

Thanks
Ricky
Shashi Kant
Ranch Hand

Joined: Aug 08, 2006
Posts: 117
Hi Ricky

Sorry please ignore my previous post.
Just try the following code
Hope this will help you




Regards
Shashikant
Ricky James
Ranch Hand

Joined: Mar 26, 2007
Posts: 83
Originally posted by Shashikant Dahatonde:
Hi Ricky

Sorry please ignore my previous post.
Just try the following code
Hope this will help you




Regards
Shashikant


Perfect!
It worked. So basically we store the value in a 'temp' variable and then assign that value into x.
Brilliant.

Thanks
Ricky
 
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