Lecture Notes on 2 Jul 2014

// Template for Day.java

import java.util.*;

public class Day
{
  public static void main (String[] args)
  {
    // Create Scanner object
    Scanner sc = new Scanner (System.in);

    // Prompt the user to enter year
    int year = 0;
    do
    {
      System.out.print ("Enter year: ");
      year = sc.nextInt();
    } while ((year < 1900) || (year > 2100));
    System.out.println (year);
  }
}


# Fun with Loops
import java.util.*;

public class Num
{
  public static void main (String[] args)
  {
    // Create a Scanner object
    Scanner sc = new Scanner (System.in);

    // Prompt the user to enter a positive number
    System.out.print ("Enter a number: ");

    // Read the number
    int n = sc.nextInt();
    int n_orig = n;

    // Sum the digits of the number
    int sum = 0;
    while (n > 0)
    {
      sum += n % 10;
      n = n / 10;
    }
    System.out.println ("Sum digits = " + sum);


    // Reverse the number
    n = n_orig;
    int rev_num = 0;
    while (n > 0)
    {
      rev_num = rev_num * 10 + (n % 10);
      n = n / 10;
    }
    System.out.println ("Reverse number = " + rev_num);

    // Check if the number is palindromic
    if (n_orig == rev_num)
      System.out.println (n_orig + " is palindromic");
    else
      System.out.println (n_orig + " is not palindromic");

    // Sum divisors of a number
    int sum_div = 0;
    n = n_orig;
    int limit = n / 2;
    for (int i = 1; i <= limit; i++)
    {
      if (n % i == 0)
        sum_div += i;
    }
    if (n == sum_div)
      System.out.println (n + " is a perfect number");
    else
      System.out.println (n + " is not a perfect number");

    // Test if the number is prime
    limit = (int) (Math.sqrt (n)) + 1;
    boolean is_prime = true;
    for (int i = 2; i < limit; i++)
    {
      if (n % i == 0)
      {
        is_prime = false;
	break;
      }
    }
    if (is_prime)
      System.out.println (n + " is prime");
    else
      System.out.println (n + " is not prime");

  }
}