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Thread: How should I start creating this program? Help

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    Default How should I start creating this program? Help

    A locker room has lockers numbered 0,1,2,...,1023 . All lockers are initially closed. The first person walks in and flips every locker The 2nd person flips every other locker (starting at 0) The 3rd person flips every third locker (starting at 0) . . . The 1024 person flips every 1024 locker (starting at 0) At the end, which lockers are open and which are closed?

    What the program must do:
    Write a program that creates an array of 1024 indices of type Boolean. Each index will represent a locker. You may assume that when the Boolean value is false, the locker is closed and when the value is true, the locker is open. This program will determine which lockers are open and closed at the end of the procedure above.
    So it will output the locker number and whether or not it is open or closed.

    For starters I was thinking to create an array called
    boolean[] Lockers = new boolean[1024];
    which will create 1024 indices with either true or false (open or closed) elements.
    What I don't know is how to make every person go to their correct interval locker, and put it into a loop. When helping please don't use advanced code I have only learned arrays, while/dowhile/for loops, bubble sort*, user input.
    I'm a complete newb at Java so any help would be appreciated.


    *I also think bubble sort should be applied here, but I don't know how to apply it.
    The following code is an unfinished bubble sorting program that I don't understand how to complete.
    int []x = {4, 2, 3,5,1};
    		int temp;
     
    		for (int c=0; c<x.length-1; c++){
    			if (x[c]>x[c+1]){
    				temp = x[c+1];
    				x[c+1]=x[c];
    				x[c] = temp;
    			}
    		}
    For the code above, the for-loop will move through the array x and swap any values if the current index is greater than the next index. To complete the bubble sort, the for loop above needs to be repeated until no swaps are made. Using the code above, add a Boolean variable called swap and a conditional loop that will repeat the for-loop until no more swaps are made.


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    Default Re: How should I start creating this program? Help

    What does "flipping" a locker mean? Change its door's status: if open close it, if closed open it?

    If you were to write a for loop for every door flipper, what would the code look like for the first 4 flippers?
    Looking at that code should show you a pattern that can then be used for the 1024 flippers.

    Hint: with boolean variables, the ! operator will change (flip) its value. Every slot in an array can be treated as a variable: theArray[index] is the same as a variable.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: How should I start creating this program? Help

    'flipping' a locker would mean either to open or close it. Depending on the state that it's in, it will always do the opposite.
    Also how would I make it so an individual door flipper flips the correct door?

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    Default Re: How should I start creating this program? Help

    how would I make it so an individual door flipper flips the correct door?
    Use the for loop's control variable. The variable can be incremented/decremented by any value, not just one:
    for(int x=0; x < max; x += incrVal) {
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: How should I start creating this program? Help

    I would recommend using the current value of your counter to also determine the increment.

    Meaning, have a for loop that runs 1024 times. The number in the counter variable will tell us which person is running through (i.e. when it's 3, that means it's the fourth person going, since it starts counting at 0)
    Inside that, have a for loop that simulates the person running through the locker room opening/closing lockers. The increment for this inside loop should be the current value of the counter of the outer loop.

    Example of this situation:

    int x, y;
     
    for (x = 0;x < 1024;x++) { //Outer loop. Increments by 1
        for (y = 0;y < 1024;y += x + 1) { //Inner loop, increments by whatever the value of the outer loops is, +1
            //flip locker at the 'y' location
        }
    }


    --- Update ---

    Quote Originally Posted by illegit View Post
    'flipping' a locker would mean either to open or close it. Depending on the state that it's in, it will always do the opposite.
    Also how would I make it so an individual door flipper flips the correct door?
    Lockers[x] = !Lockers[x]

    ^ Not 100% on that but that's my first thought...I'm still learning too (;

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    Default Re: How should I start creating this program? Help

    How would I make the program output the locker number it is at, and whether or not it is open/closed.
    output:
    1 closed
    2 open
    3 closed
    ...

    edit:
    for(int c=0; c<Lockers.length; c++) {
    	System.out.println(c +" " + Lockers[c]);
    }
    had to add the space between them to fix the error

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    Default Re: How should I start creating this program? Help

    Also, how can I make my boolean values output whether or not it is open/closed rather then true/false

    --- Update ---

    Quote Originally Posted by rpressler View Post
    I would recommend using the current value of your counter to also determine the increment.

    Meaning, have a for loop that runs 1024 times. The number in the counter variable will tell us which person is running through (i.e. when it's 3, that means it's the fourth person going, since it starts counting at 0)
    Inside that, have a for loop that simulates the person running through the locker room opening/closing lockers. The increment for this inside loop should be the current value of the counter of the outer loop.
    So like this:
    boolean[] Lockers = new boolean[1024];
    	for(int c=0; c<Lockers.length; c++) {
    		for(int y=0; y<Lockers.length; y+=c+1) {
    			Lockers[y]=!Lockers[y]; 
    		System.out.println(Lockers[y]);
    			}
    		}
    ?

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    Default Re: How should I start creating this program? Help

    When you need to make a program do something, try to break it down into steps you can do one step at a time.

    What you want to do is print if a locker is open or closed. So pseudo code may look like this:

    print "locker number " + lockerNumber + " is"
    if : the locker value is true (this means open)
      println " open."
    else
     println " closed."
    ...and you want to do that "for each" locker, so set up a loop to go through each one

    In the end you should see one of the following for each locker number:
    Locker number 0 is Open.
    Locker number 0 is Closed.
    ...but with the correct locker number depending on which number the loop is on

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    Default Re: How should I start creating this program? Help

    This is a good place to use the ternary operator. Google it for examples. It works the same in several languages.
    It can work like an inline method. Something like this:
    print("some text " + (boolean_expression ? "true message" : "false message"));
    The part in ()s will return one of two Strings depending on the value of boolean_expression.
    If you don't understand my answer, don't ignore it, ask a question.

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