Question

I have an assignment/project to write a program that displays the integers between 1 and 100 that are divisible by 6 or 7, but not both. It does not work the way I’ve written it below. Is my boolean value correct for what the question is asking?

import acm program.*;

public class SixAndSeven extends ConsoleProgram {
    public void run() {
        for (int n = 1; n < 100; n++) {
            boolean year = (n % 6 ==0) ||
                (n % 7 ==0) &&
                !(n % 6 == 0) &&
                ( n % 7 ==0);

             if (year) {
                 println(year);
             }
        }
    }
}

Answer 1

You should do the below

boolean year = ((n % 6 ==0) || (n % 7 ==0)) && !((n % 6 == 0) && ( n % 7 ==0));

Basically group the 2 sets of conditions within a () before negating, so that the conditions apply correctly to both.

To make it more readable, you could do this.. (though perhaps overkill..)

boolean divisbleby6 = n%6 == 0;
boolean divisbleby7 = n%7 == 0;
boolean divisibleby6and7 = divisbleby6 && divisbleby7 ;

boolean year = (divisbleby6 || divisbleby7) && !divisibleby6and7 ;

or the clever method suggested by Mel (possibly harder to understand at a glance), which returns true only if one but not both conditions are true.

boolean year = divisbleby6 != divisbleby7;

P.S. Additionally, as user1333371 suggests, you probably want to do println(n);