1.SUM of DIGITS in an integer

/*
 Write a code to find the SUM of DIGITS in an integer
 */
import java.util.Scanner;
public class AddDigits {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int sum = 0;
        while(number > 0){
            int x = number % 10;
            sum += x;
            number /= 10;
        }
        System.out.println(sum);
    }
}

2.ARMSTRONG NUMBER or NOT

/*
  To find whether the number is ARMSTRONG NUMBER or NOT
 */
import java.util.*;
import java.io.*;

public class ArmstrongNumber {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int temp = number;
        int sum = 0;
        String num = Integer.toString(number); // converting int to string
        int size = num.length();              // finding and storing the number of digits 
        while(number>0){
            int x = number % 10;
            sum = sum + (int)Math.pow(x,size);
            number /= 10;
        }
        if(sum==temp){
            System.out.println("Armstrong Number");
        }else{
            System.out.println("Not a Armstrong Number");
        }
    }
}

3.ODD or EVEN number

/*
 Write a code to check whether the number is ODD or EVEN
 */
import java.util.*;

public class CheckOddEven {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        if(number%2==0){
            System.out.println("Even");
        }else{
            System.out.println("Odd");
        }
    }
}

4.PALINDROME number or NOT

/*
 Write a code to check whether the number is PALINDROME or NOT
*/
import java.util.*;

public class CheckPalindrome {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number  = sc.nextInt();
        int temp = number;
        int rev = 0;
        while(number > 0 ){
            int x = number%10;
            rev = rev*10 + x;
            number /= 10;
        }
        System.out.println(rev == temp ? "It is a palindrome" : "It is NOT a palindrome");
    }
}

5.PRIME number or NOT

/*
 Write a code to check whether the number is PRIME or NOT
*/

import java.util.*;
import java.io.*;

class CheckPrimeNumber{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int count  = 0;
        for(int i = 2; i < number/2; i++){
            if(number % i == 0){
                count++;
            }
        }
        System.out.println(count == 0 ? "Prime number" : "NOT a prime number");
    }
}

6.COUNT DIGITS in an integer

/*
 Write a code to COUNT the DIGITS in a number
*/

import java.util.*;
import java.io.*;

public class CountDigits {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int count = 0;
        while(number > 0){
            count++;
            number /= 10;
        }
        System.out.println(count);
    }
}

7.FACTORIAL of a number

/*
 Write a code to find the factorial of a number
*/
import java.util.*;

public class Factorial {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int fact = 1;
        for(int i = 1; i <= number; i++){
            fact = fact*i;
        }
        System.out.println(fact);
    }
}

8.FIBONACCI Series

/*
 Write a code to write fibonaci series upto a given number
*/
import java.util.*;

public class Fibonacci{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        int a = 0;
        int b = 1, c;
        for(int i = 1; i <= num; i++){
            c = a + b;
            System.out.print(c+" ");
            a = b;
            b = c;
        }
    }
}

9.NATURAL number SERIES

/*
 Write a code to print NATURAL NUMBERS
*/

import java.util.*;
import java.io.*;

public class PrintNaturalNumbers {
    public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number = sc.nextInt();
    for(int i = 1; i <= number; i++){
        System.out.print(i+" ");
    }
    }
}

10.REVERSE the DIGITS in an integer

/*
 Write a code to REVERSE the DIGITS in an integer
*/
import java.util.*;

public class ReverseDigits {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int rev = 0;
        while(number > 0){
            int x = number % 10;
            rev = rev*10 + x;
            number /= 10;
        }
        System.out.println(rev);
    }
}

11.STRONG NUMBER or NOT

/*
 Write a code to check whether the input is STRONG NUMBER or NOT
*/
import java.util.*;
import java.io.*;

public class StrongNumber {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int sum = 0;
        int temp = number;
        while(number > 0){
            int x = number % 10;
            sum = sum + fact(x);
            number /= 10;
        }
        if(sum==temp){
            System.out.println("Strong Number");
        }else{
            System.out.println("Not a Strong Number");
        }
    }
    public static int fact(int number){
        int fact = 1;
        for(int i = 1; i <= number; i++){
            fact = fact*i;
        }
        return fact;
    }
}

12.SUM of NATURAL NUMBERS

/*
 Write a code to find the SUM of First Natural Numbers
*/
import java.util.*;

class SumOfNaturalNumbers{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int number = sc.nextInt();
        int sum = 0;
        for(int i=1 ;i <= number; i++){
            sum += i;
        }
        System.out.println(sum);
    }
}

13.SWAP 2 numbers using Temporary Variable

/*
 Write a code to swap two numbers using temporary variable
 */
import java.util.*;

public class SwapNumbers1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter 2 numbers: ");
        int number1 = sc.nextInt();
        int number2 = sc.nextInt();
        System.out.println("Numbers before swapping: "+number1+","+number2);
        int temp = number1;
        number1 = number2;
        number2 = temp;
        System.out.println("Numbers after swapping: "+number1+","+number2);
    }
}

14.SWAP 2 numbers using Arithmetic Operations

/*
 Write a code to swap two numbers using arithmetic operations
 */
import java.util.*;

public class SwapNumbers2 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter 2 numbers:");
        int num1 = sc.nextInt();
        int num2 = sc.nextInt();
        System.out.println("Numbers before swapping: "+num1+","+num2);
        num1 = num1 + num2;
        num2 = num1 - num2;
        num1 = num1 - num2;
        System.out.println("Numbers after swapping: "+num1+","+num2);
    }
}

15.HCF of 2 numbers

/*
 Write a code to find the HCF of 2 numbers
 */
import java.util.Scanner;
public class HCFOfTwoNumbers {
   public static void main(String args[]){
      int a, b, i, hcf = 0;
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter number 1 :");
      a = sc.nextInt();
      System.out.println("Enter number 2 : ");
      b = sc.nextInt();

      for(i = 1; i <= a || i <= b; i++) {
         if( a%i == 0 && b%i == 0 )
         hcf = i;
      }
      System.out.println("HCF of given two numbers is : "+hcf);
   }
}

16.LCM of 2 numbers

/*
 Write a code to find the LCM of 2 numbers
 */
public class LCMofTwoNumbers{
  public static void main(String[] args) {
    int lcm = 0;
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter number 1 :");
    int a = sc.nextInt();
    System.out.println("Enter number 2 : ");
    int b = sc.nextInt();
    lcm = (n1 > n2) ? n1 : n2;
    while(true) {
      if( lcm % n1 == 0 && lcm % n2 == 0 ) {
        System.out.printf("The LCM of 2 numbers is : "+lcm);
        break;
      }
      ++lcm;
    }
  }
}