Java multiplication using Recursion

Question

I am writing a simple code in Java that is using recursion. I want to show the product of two numbers that a user will enter. I managed to do that using recursion, but stuck at the point where I want to show that the product could be written as (example) 10*5 = 5+5+5+5+5+5+5+5+5+5 (10 times), or 12*3 = 3+3+3+3+3+3+3+3+3+3+3+3 (12 times). Here is my code so far. In the code i put a comment where it should be written (example). Thanks.

import java.util.Scanner;

public class RecursiveMultiplication {

public static void main(String[] args) {
    Scanner key = new Scanner(System.in);
    int a, b;
    System.out.print("Enter first number: ");
    a = key.nextInt();
    System.out.print("Enter second number: ");
    b = key.nextInt();
    System.out.println("The product of " + a + " and "
            + b + " is: " + multiRec(a, b));
    System.out.println("It could also be written as: ");   //Here should product be broken into smaller numbers


}

public static int multiRec(int x, int y) {
    if (x == 0 || y == 0) {
        return 0;
    } else {
        if (x == 1) {
            return y;
        } else {
            return x + (multiRec(x, y - 1));
        }
    }

  }

}

Is there a specific problem that you are encountering with the code? — Castaglia
– Castaglia, Commented Mar 3, 2016 at 4:33
The problem is that I don't know how to break the product into smaller numbers and show it to a user. As I said in the example (10*5 = 50). Now, I want to write that product as 5+5+5+5+5+5+5+5+5+5 on the screen — Ivanko
– Ivanko, Commented Mar 3, 2016 at 4:52

Scary Wombat · Accepted Answer · 2016-03-03 04:16:41Z

3

A StringBuilder should be defiend as

StringBuilder buf = new StringBuilder (a);

Pass this StringBuilder paramater into multiRec

and then change multiRec to be

public static int multiRec(int x, int y, StringBuilder buf) {
    if (x == 0 || y == 0) {
        return 0;
    } else {
        if (x == 1) {
            return y;
        } else {
            buf.append (" + ").append (x);
            return x + (multiRec(x, y - 1, buf));
        }
    }

  }

}

Then when completed simply printout its value

answered Mar 3, 2016 at 4:16

Scary Wombat

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Comments

faizal vasaya · Accepted Answer · 2016-03-03 08:26:09Z

0

    import java.util.Scanner;

public class RecursiveMultiplication {
    public static void main(String[] args) {
        Scanner key = new Scanner(System.in);
       int a , b;
        System.out.print("Enter first number: ");
        a = key.nextInt();
        System.out.print("Enter second number: ");
        b = key.nextInt();
        System.out.printf("%d %s %d %s",a , "*" , b ,"= ");
        System.out.println("\nThe product of " + a + " and "
                + b + " is: " + multiRec(b, a));
       // System.out.println("It could also be written as: ");   //Here should product be broken into smaller numbers


    }

    public static int multiRec(int x, int y) {

        if (x == 0 || y == 0) {
            return 0;
        } else {
            System.out.print(x+" ");
            if (y == 1) {
                return x;
            } else {
                System.out.print(" + ");
                return x + (multiRec(x, y - 1));
            }
        }

      }
}

edited Mar 3, 2016 at 8:26

answered Mar 3, 2016 at 4:34

faizal vasaya

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3 Comments

Ivanko Over a year ago

Both examples helped me to understand how to achieve what I need. The only thing is formatting. In both cases there is a + sign at the end of the last smaller number. Here is what I mean by that. Output: Enter first number: 10 Enter second number: 5 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + The product of 10 and 5 is: 50

faizal vasaya Over a year ago

In the above code , I have already taken care about the last "+" symbol.

Ivanko Over a year ago

Sorry, you did. I appreciate your help. I found different problem now when i put 10 as first number and 5 as second number, here is the output : Enter first number: 10 Enter second number: 5 10 * 5 = 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 The product of 10 and 5 is: 46 (Don't know why it is 46) Also, i tried to write "The product of 10 and 5 is 50" and then below that "It could be also written as: 5+5+5+5+5+5+5+5+5+5.

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