Question

4.9: Population
Write a program that will predict the size of a population of organisms. The program should ask the user for the starting number of organisms, their average daily population increase (as a percentage, expressed as a fraction in decimal form: for example 0.052 would mean a 5.2% increase each day), and the number of days they will multiply. A loop should display the size of the population for each day.

Prompts, Output Labels and Messages.The three input data should be prompted for with the following prompts: "Enter the starting number organisms: ", "Enter the daily increase: ", and "Enter the number of days the organisms will multiply: " respectively. After the input has been read in successfully, a table is produced, for example:

      -----------------------------
      2            300.0
      4            675.0
Under the heading is a line of 29 dashes followed by one line for each day, showing the day number and the population at the beginning of that day.

Input Validation.Do not accept a number less than 2 for the starting size of the population. If the user fails to satisfy this print a line with this message "Invalid. Must be at least 2. Re-enter: " and try to read the value. Similarly, do not accept a negative number for average daily population increase, using the message "Invalid. Enter a non-negative number: " and retrying. Finally, do not accept a number less than 1 for the number of days they will multiply and use the message "Invalid. Enter 1 or more: "

Answer 1

Program Screenshots:

Sample Output:

Code to Copy:

import java.util.Scanner;

// Declare a class.

public class PopulationGrowth {

   // start the main method.
   public static void main(String[] args) {

       // Declare the object of scanner class.
       Scanner scan = new Scanner(System.in);

       // Declare the variables.
       double pop_count, D_growth;

       int N_Days;

       // Prompt the user to enter the strting number of organism.
       System.out.print("Enter the starting number organisms: ");

       // input value.
       pop_count = scan.nextDouble();

       // Start the while loop
       while (pop_count < 2) {

           // Display the result on console.
           System.out.print("Invalid. Must be at least 2. Re-enter:");

           // Input value.
           pop_count = scan.nextDouble();

       }

       // Prompt the user to enter daily increase
       System.out.print("Enter the daily increase: ");

       // Get the value.
       D_growth = scan.nextDouble();

       // Start the while loop
       while (D_growth < 0)

       {
           // Prompt the user to enter non-negative number.
           System.out.print("Invalid. Enter a non-negative number: ");

           // Get the value.
           D_growth = scan.nextDouble();

       }

       // prompt the user to enter value.
       System.out.print("Enter the number of days the organisms will multiply: ");

       N_Days = scan.nextInt();

       // Start the while loop
       while (N_Days < 1)

       {
           // Prompt the user to enter value.
           System.out.print("Invalid. Enter 1 or more: ");

           // get the number.
           N_Days = scan.nextInt();

       }

       // Display the header.
       System.out.println("Day" + "\t\t" + "pop_count");

       // start the for loop
       for (int i = 0; i < 29; i++)

           System.out.print("-");

       int i = 1;

       System.out.println();

       // Start the for loop
       while (i <= N_Days)

       {

           // Display the value.
           System.out.println(i + "\t\t" + Math.round(pop_count));

           // Calculate the value.
           pop_count += pop_count * D_growth;
           i++;
       }
       scan.close();
   }

}