Greenfoot

davemib123

2013/8/9

#

Hi, having a try with loops and have come to a slight problem. I have read that their are 3 types of loops, I have managed to get the for and while working, but do while doesnt work as the previous two. The first two generate 3 worms and if the number falls below 3 another worm is added. Whereas do while keeps adding them. This is my attempt:

        //loop1
        while (getObjects(Worm.class).size() < 3) {
            addObject(new Worm(), Greenfoot.getRandomNumber(530), Greenfoot.getRandomNumber(500));
        } 

        //loop2
        for (int i = getObjects(Worm.class).size(); i < 3; i++) {  
            addObject(new Worm(), Greenfoot.getRandomNumber(530), Greenfoot.getRandomNumber(500));
        }

        //loop3
        do
        {
            addObject(new Worm(), Greenfoot.getRandomNumber(530), Greenfoot.getRandomNumber(500));
        }
        while (getObjects(Worm.class).size() < 3);

Any suggestions ?

bourne

2013/8/9

#

"the statements within the do block are always executed at least once" http://docs.oracle.com/javase/tutorial/java/nutsandbolts/while.html

davemib123

2013/8/9

#

yea I read that, but how do I stop the worms spawning for loop 3. I've tried this, but it just crashes greenfoot:

int i = getObjects(Worm.class).size();
        do
        {
           addObject(new Worm(), Greenfoot.getRandomNumber(530), Greenfoot.getRandomNumber(500));
          i++;
        }
        while (i < 3);

danpost

2013/8/9

#

When you use a do-while loop, it always will execute once each time before checking the condition. You want the condition to be checked before executing the code; so you should use a basic while loop. Actually better would be to use a standard if statement:

if (getObjects(Worm.class).size() < 3) addObject(new Worm(), Greenfoot.getRandomNumber(530), Greenfoot.getRandomNumber(500));

Even if two are removed in the same act cycle, have one replaced each act cycle would not be noticeably different than replacing both at the same time.

davemib123

2013/8/10

#

thanks for the info Danpost, but I was trying to figure how to use do-while for the same solution.

danpost

2013/8/10

#

Because do-while works differently than while, you cannot expect them to be used for the same thing. However, with slight modification of your code it could be done:

if (getObjects(Worm.class).size() < 3)
{
    do
    {
        addObject(new Worm(), Greenfoot.getRandomNumber(530), Greenfoot.getRandomNumber(500));
    } while getObjects(Worm.class).size() < 3);
}

This will add the beforehand check while maintaining a do-while loop.

danpost

2013/8/10

#

Another way to handle it is this:

Worm worm = null; // to reference new worms
do
{
    worm = new Worm();
    addObject(worm, Greenfoot.getRandomNumber(530), Greenfoot.getRandomNumber(500));
} while getObjects(Worm.class).size() < 4); // raised to 4
removeObject(worm); // removing last worm added

Although this method would use up more resources than necessary, it will keep the number of worms at three while maintaining a do-while loop.

davemib123

2013/8/10

#

that's great. thanks danpost :)

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