Lecture Notes on 19 Sep 2011

Sum the following series to 10 terms

1 - 1/3 + 1/5 - 1/7 ...

double sum = 0.0;

// First solution
for (int i = 1; i <= 10;  i++)
{
  if (i % 2 == 1)
  {
    sum = sum + 1.0 / (2 * i - 1);
  }
  else
  {
    sum = sum - 1.0 / (2 * i - 1);
  }
}

// Second more elegant solution
double sign = 1.0;
for (int i = 1; i <= 10; i++)
{
  sum = sum + sign / (2 * i - 1);
  sign = (-1) * sign;
}


import java.util.Scanner;

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

    // Read user input
    int n;
    do
    {
      System.out.print ("Enter positive number: ");
      n = sc.nextInt();
    } while (n < 0);

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

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