Not getting the correct response for an automorphic number-CodePudding

I was writing a program to check if a number is automorphic or not. I decided to test the program. But somehow, when I entered a number greater than 9376, it said that it was not an automorphic number.

Link for automorphic number: Automorphic number

import java.util.Scanner;
public class test{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int copy=n,ex=0;
        while(n!=0){
            n/=10;
            ex  ;
        }
        if((copy*copy)%(Math.pow(10,ex))==copy){
            System.out.println(copy " is an automorphic number.");
        }
        else{
            System.out.println(copy " is not an automorphic number.");
        }
    }
}

I tried it with 5, 25, 76, 376 and it gave me the correct response. But when I entered 90625 or other numbers, it replied in negative.

Output for reference:

90625
90625 is not an automorphic number.
9376
9376 is an automorphic number.

CodePudding user response：

For large integers (like 90625), squaring it (copy * copy) will result in an integer overflow.

If you print the value of copy * copy for 90625, you'll get -377043967.

To fix this, you can make the variable copy of type long.

However, you have to decide what is the maximum or largest number you'll ever want this to work for. If the square of that number won't fit within the bounds of a long, then you'd have to use a BigInteger. Since you had the input as an int, using a long should be good enough for you (A long can hold the result of Integer.MAX_VALUE * Integer.MAX_VALUE).