Generate Natural Logarithm of 2 Customly

Question

I know I could generate it using Math.log(2) but I when I try to make up my own program to generate a natural log of 2 it continuously print 1. This is my code:

import java.math.BigDecimal;
import java.util.Scanner;


public class Ques11 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        BigDecimal sum = new BigDecimal(1);
        for(int i = 2; i <= n; i++) {
            sum.add(new BigDecimal(1/n));
        }
        System.out.print(sum.setScale(10).toPlainString());
    }
}

I have tried to use float, double and int and in the end used BigDecimal but I still got 1 as the result I don't know why.

P.S It actually throws InputMismatchException when big numbers are given i.e greater than 2000000000 or 2 Billion.

What makes you think this computes the log of 2? You seem to be computing `1 + (n-1) * 1/n` (once the integer division is corrected). — Mark Dickinson, Aug 16 '14 at 17:21

score 1 · Accepted Answer · answered Aug 16 '14 at 17:17

n is defined as an int and 1 is an int literal. When you divide two ints you use integer arithmetic, which would return only the whole part of the fraction - in your case, 0. To rectify this, you should use doubles:

public class Ques11 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        double d = scan.nextInt(); // Note we're assigning to a double
        BigDecimal sum = new BigDecimal(1);
        for(int i = 2; i <= d; i++) {
            sum.add(new BigDecimal(1.0/d));
        }
        System.out.print(sum.setScale(10).toPlainString());
    }
}

Generate Natural Logarithm of 2 Customly

1 Answers1