/* Craig Persiko  -  CS 111A
   PP4.java - Solution to Homework 6
   Jackalope population program

   This program calculates jackalope populations after
   a specified number of generations pass.
*/

import java.util.Scanner;

public class PP4
{
  public static void main(String args[])
  {
    Scanner keyIn = new Scanner(System.in);
    int starting_population, pop, num_generations;
    String calc_again;
    final double BIRTH_RATE = 0.03, DEATH_RATE = 0.01;

    do
    {
      System.out.print("How many jackalopes do you have? ");
      starting_population = keyIn.nextInt();
      System.out.print("How many generations do you want to wait? ");
      num_generations = keyIn.nextInt();
      keyIn.nextLine(); // dispose of the newline

      pop = starting_population;
      // pop always equals the current population, which is updated each generation
      for(int g=0; g < num_generations; g++)
      {
        pop += (int)(pop * BIRTH_RATE);
        pop -= (int)(pop * DEATH_RATE);  // make sure we don't subtract a fraction of an animal
      }

      System.out.println("If you start with " + starting_population
                         + " jackalopes and wait " + num_generations
                         + " generations,\nyou'll end up with a total of "
                         + pop + " of them.");

      System.out.print("Do you want to calculate another population? ");
      calc_again = keyIn.nextLine();
    }while(Character.toLowerCase(calc_again.charAt(0)) == 'y');
  }
}

/* Sample Output:

How many jackalopes do you have? 200
How many generations do you want to wait? 1
If you start with 200 jackalopes and wait 1 generations,
you'll end up with a total of 204 of them.

Do you want to calculate another population? y

How many jackalopes do you have? 132
How many generations do you want to wait? 2
If you start with 132 jackalopes and wait 2 generations,
you'll end up with a total of 137 of them.

Do you want to calculate another population? y

How many jackalopes do you have? 40
How many generations do you want to wait? 100
If you start with 40 jackalopes and wait 100 generations,
you'll end up with a total of 291 of them.

Do you want to calculate another population? n

*/