How does the function powRec(x,n-1) performs an exponentiation?

Question

class PowerRec
{
   static double powRec(double x, int power)
   {
      if (power == 1){
        return x;        
      }      
      return x * powRec(x, power - 1);
   }

  public static void main(String args[])
  {
    double x = 2;
    System.out.println (x + " to the fourth is " + powRec (x, 4));
  }    
}

It doesn't. However `x * (x ^ (n - 1)) == x ^ n` – Elliott Frisch Feb 08 '18 at 00:56 — Elliott Frisch, Feb 08 '18 at 00:56
Doing some code layout revealed a marouding line. Fixed it. – user unknown Feb 18 '18 at 15:24 — user unknown, Feb 18 '18 at 15:24

score 1 · Answer 1 · answered Feb 08 '18 at 01:14

1

you have two returning statement in a row in your code. And wrong powRec method

 static double powRec(double x, int power) {
    if (power == 0) {

        return 1;


    }
    return x * powRec(x, power - 1);
}

answered Feb 08 '18 at 01:14

loljeene

79
1
6

Yeah, I made a mistake, but I still don't understand how 'powRec(x, power-1) ' works? – sctts-lol Feb 08 '18 at 01:22
You use recursion method call. Method powRec(x,4) call powRec(x,3), then powRec(x,2)... Until power==0. You can read https://en.wikipedia.org/wiki/Recursion_(computer_science) – loljeene Feb 08 '18 at 01:34

score 0 · Answer 2 · answered Feb 18 '18 at 15:27

0

a³ = a * a ² = a * (a * a)

This is, what the code essentially does.

Now your new homework: Replace (x * y) with a call to mul (x, y), and solve the problem of multiplication with addition in the same habit.

answered Feb 18 '18 at 15:27

user unknown

35,537
11
75
121

How does the function powRec(x,n-1) performs an exponentiation?

2 Answers2