/**
     * Method: sieveOfEratosthenes
     * This method takes a boolean array
     * This method changes all non-prime numbers up to the length of the array to false
     *
     * This method is by far one of the most difficult we have had so far
     *
     * A boolean array is like a row of light switches.
     * For this method they all should start up, ON, or true
     * If a light switch is ON, then the number is prime.
     * Your code should start at the number 2, and turn all 2's off
     * It should then go to 3 and turn all 3's off.
     * It should then go to 4 and turn all 4's off (you can skip this if you want)
     * etc.
     *
     * To find out how many elements are in an array, you use the array name, a period
     * and the keyword length.
     *
     */
    public static boolean[] sieveOfEratosthenes(boolean [] a){

        //Turn off, or set to false, all array spots that are not prime.
        //Yes, this is a double for loop, or a for loop inside a for loop
        //You will really need to think about this.  Just dropping in numbers won't do it
        //Remember for loops have 3 important things.  A starting point, and ending point,
        //and an increment.  You can change all 3 items.

        //You may want to figure out the inside for loop first, i.e. get it to remove all
        //the 2's.  Then wrap a for loop around that and make the inside for loop more
        //general
        for(int i=0; i<a.length(); i++)
            a[i]=true;

        for(int i = 2; i<a.length(); i++){
            if(a[i]){
                for(int j=i; j*i<a.length; j++)
                {
                    a[j*i]=false;
                }
        }

        }

        return a;
    }


}