How to Easily Check Whether a Number is Automorphic in Java

There are several articles on "how to check in Java whether a number is Automorphich or not" which you can find on the Internet including some from popular websites like GeeksforGeeks and JavaTpoint. But they all have a similar problem. They are not beginners friendly.

In this article, I will show you a beginner-friendly approach to find whether a number is Automorphic or not in Java.

What is an Automorphich Number?

An Automorphic Number is a number whose square has the exact number as its last digit. For example, 25 which is the square of 5 contains 5 as its last digit. An example of a two-digit number is 5776 which is the square of 76 and ends with 76. Some other examples are 625 which is the square of 25 and ends with 25.

Approach to Solve the Program

Let's take a look at the easy approach to solving the problem first.

• Input number from the user
• Assign it to another variable (here the variable is p)
• Store the square of the number in a variable (here sq)
• With a loop check if the last digits of both numbers are the same or not
• Whether the last digits are the same or not can be checked with a simple condition (n % 10 == sq % 10)
• With the help of a counter variable (here c) take a record of how many last digits are similar
• Outside the loop, check with an if-else condition whether the counter variable is greater than 0 or not (counter variable c is initialized 0).

![Screenshot of the Automorphic Number Program in Java](https://cdn.hashnode.com/res/hashnode/image/upload/v1670005718985/9a8c69ff-af3a-40ea-a637-aba9bdc87560.jpeg align="center")

Code

import java.util.Scanner;
class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int i, n, sq, c=0;
        
       System.out.println("Enter a number to check for Automorphic Number");
                n = in.nextInt();
                sq = n * n;

                for (i = n; n > 0; n = n / 10) {
                    if (n % 10 == sq % 10)
                        c++;
                    sq = sq / 10;

                }

                if (c > 0)
                    System.out.println("Automorphic Number");
                else
                    System.out.println("Not an Automorphic Number");
    }
}

Got a problem with For Loop? Here it is solved with While Loop

import java.util.Scanner;
class Main
{
  public static void main (String[]args)
  {
    Scanner in = new Scanner (System.in);
    int n, sq, p, c = 0;

      System.out.println ("Enter a number to check for Automorphic Number");
      n = in.nextInt();
      p = n;
      sq = n * n;

    while (n > 0)
      {
	if (n % 10 == sq % 10)
	  c++;
	n = n / 10;
	sq = sq / 10;

      }

    if (c > 0)
        System.out.println ("Automorphic Number");
    else
      System.out.println ("Not an Automorphic Number");
  }
}

Code Explanation

The program is simple. We just have to check if the last digits of a number's square are equal to the number or not.

I have taken five variables:

• i - this variable is kind of useless
• n - to store the number input by the user
• sq - to store the square of the number
• p - to store the number for verification at last as the variable n will become 0 after the control exits from the loop
• c - it is a counter variable used here to check whether the number comes at the end of its square or not

for (i = n; n > 0; n = n / 10) { if (n % 10 == sq % 10) c++; sq = sq / 10;

The For Loop condition 'i=n' can be replaced with a semi-colon (;).

for (; n > 0; n = n / 10)

The condition inside the for loop is used to check whether the last digit of the variable n is equal to the last digit of variable sq or not. At the last of the loop, both the variables sq and n are divided by 10.

In While Loop, n = n / 10 is at the last with sq = sq / 10.

This loop continues till the value of n becomes 0. This is why previously the value of n is stored in the variable p.

Edit: There is no need for the variable p.

If the last digit of both the variables is the same, the counter variable c will be increased by 1.

After the loop is completed and n has become 0, the control will move outside the loop and then with an if-else condition we will check if the counter variable c is greater than 0 or not. If it is then the sq contains n as its last digit.

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