What am I doing wrong in Java Code Project 20 "Loan Calculator"?

Question

I need to output the loan to pay after 3 month. Every month the loan is paid by 10% of the remaining amount.
E.g. 20000 ->10% = 2000 --> 18000 to pay.

My code:
import java.util.Scanner;

public class Program
{
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int amount = scanner.nextInt();
//your code goes here
for(int x=0;x<3;x++){
amount = amount - amount /100*10;
}
System.out.println(amount);
}
}

Now the problem is, test cases 1 and 2 come back positiv but the hidden test cases (3-5) are false or wrong and I don't know why.
Thank you in advance :)

Answer 1

I honestly can't explain why. but use this inside the for:

amount -= amount*0.1;

I suppose that with your way of doing it you lose a decimal at some point ... I can't think of anything else

Answer 2

Maximilian Gamed

If you are interested you can read here about this issue:
https://pmi-sesni.medium.com/floating-point-rounding-error-in-java-5c160cb55315

The very short answer is converting binary numbers to fractions or fractions to binary numbers causes troubles.

Answer 3

I changed it to that and now it worked.
I had it like
amount =amount- amount*0.1;
Before but I got an error so I sticked with divide by 100 multiply by 10.
Thank you very much :)