Recursive Exponent Method

Question

public static int exponent(int baseNum) {
    int temp = baseNum *= baseNum;                

        return temp * exponent(baseNum);             
}

Right now the method above does n * n into infinity if I debug it, so it still works but I need this recursive method to stop after 10 times because my instructor requires us to find the exponent given a power of 10.

The method must have only one parameter, here's some examples of calling exponent:

                System.out.println ("The power of 10 in " + n + " is " + 
                    exponent(n));

So output should be:

The power of 10 in 2 is 1024

OR

The power of 10 in 5 is 9765625

Solution 1

Create an auxiliary method to do the recursion. It should have two arguments: the base and the exponent. Call it with a value of 10 for the exponent and have it recurse with (exponent-1). The base case is exponent == 0, in which case it should return 1. (You can also use exponent == 1 as a base case, in which case it should return the base.)

Solution 2

Do something like

public static int exp(int pow, int num) {
    if (pow < 1) 
        return 1; 
    else
        return num * exp(pow-1, num) ;
}

public static void main (String [] args) {     
    System.out.println (exp (10, 5));
}

and do not forget the base case (i.e a condition) which tells when to stop recursion and pop the values from the stack.

Solution 3

The following is what my instructor, Professor Penn Wu, provided in his lecture note.

public class Exp

{

 public static int exponent(int a, int n)

 {

  if (n==0) { return 1; } // base

  else // recursion

  { 

   a *= exponent(a, n-1); 

   return a; 

  }

 }


 public static void main(String[] args)

 {

  System.out.print(exponent(2, 10));

 }

}

Comments

[Luiggi Mendoza]

There's no base case in your recursive method!

[Louis Wasserman]

If you need it to stop after ten times, you need to have a variable for how many times it's recursed.

[Vishy]

You need to pass the power as an argument like power(baseName, n); decrease the power by one each time you recurse.