How to properly use Math.log?

Question

So I got this formula to calculate the number of years it takes to double any amount of money with a given interest (i)

log(2) / log(1 + (i/100) )

So here's my code:

import java.util.Scanner;

public class JavaApplication37 {

    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);  
        System.out.println("What's the interest rate?: ");
        int i = reader.nextInt(); 
        double t = (Math.log(2))/(Math.log(1+(i/100)));
        System.out.println("It takes " + t + " years before the amount has doubled");
    }
}

That gives me the output: It takes Infinity years before the amount has doubled

What did I do wrong?

Answer 1

The problem is that 100 is assumed as integer. You should rather write 100 is as 100.0 and it will run. This is because values as 1.0, 2.3 assumed as double and not float. Notice the decimal point.

so rewrite you code as below and it will run:

import java.util.Scanner;

public class JavaApplication37 {




    public static void main(String[] args) {
       Scanner reader = new Scanner(System.in);  
        System.out.println("What's the interest rate?: ");
    int i = reader.nextInt(); 
    double t = (Math.log(2))/(Math.log(1+(i/100.0)));
    System.out.println("It takes " + t + " years before the amount has doubled");

    }

}