Q:

Integer not increasing when it should

Write a program that will predict the size of a population of organisms. The program should ask
for the starting number of organisms, their average daily population increase (as a percentage),
and the number of days they will multiply. For example, a population might begin with two
organisms, have an average daily increase of 50 percent, and will be allowed to multiply for
seven days. The program should use a loop to display the size of the population for each day.
Input Validation: Do not accept a number less than 2 for the starting size of the population. Do
not accept a negative number for average daily population increase. Do not accept a number
less than 1 for the number of days they will multiply.
My issue is that each day is not increasing.
my example input is 100 organisms, 50 percent increase, and 3 days 
My output is
day 1: 100 
day 2: 100
day 3: 100
import java.util.Scanner;

 public class Population {

    public static void main(String args[]) {
           Scanner scanner = new Scanner( System.in );

        System.out.println("Please input the number of organisms");
          String inputOrganisms = scanner.nextLine();
        int numOfOrganisms = Integer.parseInt(inputOrganisms);

          System.out.println("Please input the organisms daily population 
  increase (as a percent)");
          String inputPopIncr = scanner.nextLine();
        double popIncrease = Integer.parseInt(inputPopIncr) /100;

        System.out.println("Please input the number of days the organisms will multiply");
          String inputNumOfDays = scanner.nextLine();
        int numOfDays = Integer.parseInt(inputNumOfDays);

       for (int i = 1; i < numOfDays+1; i++) {
           numOfOrganisms = numOfOrganisms += (numOfOrganisms *= popIncrease);
           System.out.println("Day " + i + ": " + numOfOrganisms);
       } 

    }

}

A:

Your problem:
In the for loop you should have
numOfOrganisms += numOfOrganisms * popIncrease;

The reason behind this is because you need to add the population increase to the existent number.
What you are doing causes an error, as you need to have only one equals in a syntax line. The second equals (the +=) isn’t being read as it is invalid.
Cheers!

