Java For Loop into Recursive function

Question

public class For {
 public static void main(String[] args){
          for(int i=2; i<=1024; i *= 2){
           System.out.println("Count is: " + i);
      }
 }




public class While {
    public static void main(String[] args){
        int i = 1;
        while (i < 1024) {
            i *= 2;
            System.out.println("Count is: " + i);
      }
 }


public class DoWhile {
     public static void main(String[] args){
        int i = 1;
        if (i < 1024) {
            do { i*=2;
                System.out.println("Count is: " + i);
            } while (i < 1024);
        }
     }

How would one convert the for loop/while loop so it does the same thing, but using a recursive function?

If this is homework, please indicate this by adding the homework tag. — Ingo
– Ingo, Commented May 4, 2011 at 10:52

David Grant · Accepted Answer · 2011-05-04 11:08:15Z

5

Like so:

public class Recursive {
    public void r(int i) {
        if (i < 1024) {
            i *= 2;
            System.out.println("Count is: " + i);
            r(i);
        }
    }

    public static void main(String[] args) {
        Recursive r = new Recursive();
        r.r(1);
    }
}

edited May 4, 2011 at 11:08

answered May 4, 2011 at 10:53

David Grant

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5 Comments

Ingo Over a year ago

-1 for being not helpful. Enabling students to solve the problem at hand is helpful, to serve them the solution on a silver tray is not, IMHO. Why should Manpreet Pangli ever care listeing to his professor, when it's so cheap to get the answer from SO?

Lukasz Over a year ago

It produces different results than the examples in OPs question. Your program starts printing from 1. Multiplication by 2 should be done before println.

Lukasz Over a year ago

@Ingo: I didn't know it's homework. There's no homework tag. I think it's not fair to -1 answers not because they are not correct, but they were given to "homework questions".

David Grant Over a year ago

@Ingo: it's hard to argue against your point, although it is a little judgemental!

Ingo Over a year ago

Yes, @David, I care about the next generation programmers, even if they're from India. And I can't stand it if people can get away with avoidance of thinking.

Fred Foo · Accepted Answer · 2011-05-04 10:53:27Z

4

Take the loop of main and put it in its own function with an argument int i. In that function, rewrite the loop to

If the loop condition is false (i >= 1024), then return
Else, recursive call with argument i*2.

Call the function with argument 1 or 2, depending on which of your programs you're rewriting (they don't entirely match).

answered May 4, 2011 at 10:53

Fred Foo

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Comments

Lukasz · Accepted Answer · 2011-05-04 11:04:49Z

1

Recurrent loop can look like this:

class Main
{
    public static void main(String[] args){
      RecWhile(1);
    }

    public static void RecWhile(int i) {
       if (i < 1024) {
         i = i*2;
         System.out.println("Count is: " + i);
         RecWhile(i);
       }
    }
}

edited May 4, 2011 at 11:04

answered May 4, 2011 at 10:59

Lukasz

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2 Comments

Lukasz Over a year ago

This answer is marked -1 not because it's incorrect, but BECAUSE it was given to a question that was not supposed to be answered this way (of course, that's not my POV; but the that's the way it is on Stack Overflow)

Ingo Over a year ago

No, that's me, not SO. If you do not see that this can only be homework, I can't help it.

satish hiremath · Accepted Answer · 2020-05-30 21:28:42Z

0

public class Test1 {

public static void main(String[] args) {

    Test1 mainFunc = new Test1();

    int[] arr = {1,2,4,3,5,6};

    int start=0;
    int end=arr.length;
    mainFunc.callRecursiveFun(start, end, arr);
}

public int callRecursiveFun(int start, int end, int[] arr) {
    int arrLen = end;
    if(arrLen == 0) {
        return 0;
    } else {

    System.out.println("Loop Index at "+start +": "+arr[start]);


    }
    return callRecursiveFun(start+1, end-1, arr);
}

}

edited May 30, 2020 at 21:28

answered May 30, 2020 at 21:22

satish hiremath

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