Understanding Recursion part II

Question

Hello;
I went back through the chapter on recursion and realized part of my problem was not understanding what happens in the steps.
Some calls are easy to understand like this one
import java.util.*
public class CountDown
private int count;
public static void main(String[] args)
CountDown countDowner = new CountDown( );
countDowner.getCount( );
countDowner.showCountDown( );
public void getCount( )
System.out.println("Enter a positive number:");
Scanner keyboard = new Scanner(System.in);
count = keyboard.nextInt( );
if (count <= 0)
System.out.println("Input must be positive.");
System.out.println("Try again.");
getCount( );//start over
public void showCountDown( )
int left;
System.out.println("Counting down:");
for (left = count; left >= 0; left--)
System.out.print(left + ", ");
System.out.println("Blast Off!");
}Here's one I'm stuck understanding ;
This program returns ten to the power of user integer.
import java.util.*;
public class tenToThe
public static void main(String[] args)
Scanner keyboard = new Scanner(System.in);
System.out.println("Please enter an integer greater than zero");
int userNumber = keyboard.nextInt();
double result = (double)tenToThe(userNumber);
System.out.println("10 to the " + userNumber + " power is "
+ result);
private static double tenToThe(int n)
if (n==0)
return 1;
else
return (tenToThe(n-1)*10);
}So when I put in three as my user integer, the first if is not true, but it looks like the next expression is equivalent to (3-1)*10 equal 20??
I don't see how they got to 1000.
Last bits. Tonight I wrote an iterative method that sums an array hoping it might give me insight how to make it recursive. This works but still stumped. What would be the steps to make it recursive?
public class iterativeSumArray
     /** iterative method returns the value of each element in array */
     public static void main(String[] args)
               int[] a = {2,3,4,5,6,7,8,9};
               System.out.println(iterativeSumArray.sumArray(a));
     private static int sumArray(int[] theArray)
          int sum = 0;
          for (int i=0; i< theArray.length-1; i++)
               sum += theArray;     
          return sum;
Thanks again for your help and patience!
Edited by: Zarnon on Feb 28, 2008 6:41 PM
Edited by: Zarnon on Feb 28, 2008 6:42 PM                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

Answer 1

if u know how to play with stacks or if u know How internally recursion works ( ofcourse with stack) , then i dont think ther is any difficulty u face while programming with recursion . (Make your data Structure fundamental clear, first . )
What would be the steps to make it recursive?
public class MySumArray
     static int sum, i, length;
     /** iterative method returns the value of each element in array */
     public static void main(String[] args)
               int[] a = {2,3,4,5,6,7,8,9};
               System.out.println(MySumArray.sumArray(a, a.length));
     private static int sumArray(int[] theArray, int length)
          if(length != 0)
               sum += theArray[length - 1];
               sumArray(theArray, --length);
          return sum;
}here i modify your code , to make it work recusively , but if u can do the same job by iterarion ( Java provide good Iterator class in java.util.*) , then dont go for recursion (it may happen u stuck in infinte recursive loop , and may stack overflow )
Hope this help..