递归使用for循环

Question

So I am trying to print out the actual process of the recursive exponent method and then the value in the end, but I am having issues with my for loop. For example if the user inputs 4 to the 4th power it should print out 4 to 4, 4 to 3, 4 to 2, etc. and then print out correct value of 4 to 4th power, but I keep getting 0 for the value in the end.

import java.util.Scanner; 

public class Recursion
{
  public static void main(String[] args)
  {
    Scanner input = new Scanner(System.in);

    System.out.println("Enter base: ");
    int baseNum = input.nextInt();

    System.out.println("Enter exponent: ");
    int expNum = input.nextInt();

    for(int i = 1; i <= baseNum; ++i)
    {

    System.out.printf("\n%d to the %d", baseNum, expNum--);

    }

    System.out.printf("\nValue is %d",power(baseNum, expNum));
  }



  public static int power(int base, int exponent)
  {
    if(base == 0)
      return 1;

    else
      return exponent * power(base - 1, exponent);
  }
}

Answer 1

You confused the base with the exponent. The power method should be defined like this:

public static int power(int base, int exponent) {
    if(exponent == 0) {
        System.out.println(1); // for display
        return 1;
    }
    else {
        int rem = power(base, exponent-1);
        if (rem > 1) {
            System.out.println(rem); // for display
        }
        return base * rem;
    }
}

USAGE

public static void main(String[] args) {
    System.out.println(power(4,2)); // prints 16
}

Answer 2

The recursive definition of exponentiation is

x^n = x * x^(n-1)

Note that the exponent decreases, not the base.

Answer 3

Power = base raised to exponent. You did it the wrong way. Correct way -

public static int power(int base, int exponent) {
    if(exponent == 0)
        return 1;
    else
        return base * power(base, exponent-1);
}

To make the above code display the intermediate results:

import java.util.Scanner;

public class Recursion {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.println("Enter base: ");
        int baseNum = input.nextInt();

        System.out.println("Enter exponent: ");
        int expNum = input.nextInt();

        int pow = power(baseNum, expNum);

    }

public static int power(int base, int exponent) {

    int pow = 0;

    if (exponent == 0) {
        pow = 1;
        System.out.println(base + " raised to " + exponent + " is " + pow);
    } else {

        pow = base * power(base, exponent - 1);
        System.out.println(base + " raised to " + exponent + " is " + pow);
    }

    return pow;

}

Answer 4

There are two problems with your code

1. The exponent is being mutated before you actually use it expNum--
2. You reverse the base and exponent in power()

Below is an edited version of your code that works

import java.util.Scanner;

public class Recursion
{

    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);

        System.out.println("Enter base: ");
        int baseNum = input.nextInt();

        System.out.println("Enter exponent: ");
        int expNum = input.nextInt();

        for (int i = 1; i <= expNum; ++i)
        {

            System.out.printf("\n%d to the %d", baseNum, i);

        }

        System.out.printf("\nValue is %d", power(baseNum, expNum));
    }

    public static int power(int base, int exponent)
    {
        if (exponent == 0)
        {
            return 1;
        }

        else
        {
            return base * power(base, exponent - 1);
        }
    }
}