Subtracting a variable in a loop in Java

Question

I'm trying to calculate how many rounds can a player play lotto and joker games with a fixed amount of money.

public static void example () {
    int money = 200;
    int lottoCost = 4;
    int jokerCost = 3;
    int costTogether = lottoCost+jokerCost;
    int rounds = 0;

    for (int i = money; i <= 0; rounds++) {
        money = money-costTogether;
    }

    System.out.println("With " + money + " euros, you can play "
                        + rounds + " rounds.");
    System.out.println("");

}

That code currently prints the text "With 200 euros, you can play 0 rounds." So it doesn't add a +1 to the rounds variable. What am I doing wrong?

If you fix the loop as suggested by others, your output will no longer be correct, since you modify the money variable. — Some programmer dude
– Some programmer dude, Commented Oct 9, 2014 at 10:53
Also, you don't need a loop to calculate the number of rounds, normal division will do the trick (and if you use this, then you incidentally "fix" the bug noticed in my previous comment). — Some programmer dude
– Some programmer dude, Commented Oct 9, 2014 at 10:54

Fredszaq · Accepted Answer · 2014-10-09 10:58:37Z

4

In general, it is good to use the same variable in the 3 parts of the for. Note that the loop initialization part (the first one int i = money) is only run once, and you don't modify i during the loop. Furthermore, the condition is false from the beginning (200 < 0) so the loop is not even run once

I think what you are looking for is a simple int division, just replace your for block with this :

rounds = money / costTogether;

edited Oct 9, 2014 at 10:58

answered Oct 9, 2014 at 10:52

Fredszaq

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1 Comment

Joffrey Over a year ago

Upvoted for the simple answer regarding the original problem instead of the OP's current little bug.

Joffrey · Accepted Answer · 2014-10-09 11:59:45Z

2

Your stopping condition is wrong, so the loop is never exectued. You should use >= instead. Also, you never change nor use i.

Here is a corrected version, using currMoney instead of i to be more meaningful.

int rounds = 0;
for (int currMoney = money; currMoney >= costTogether; currMoney -= costTogether) {
    rounds++;
}

But obviously here, you only need a simple division as @Fredszaq pointed out in his answer:

int rounds = money / costTogether;

edited Oct 9, 2014 at 11:59

answered Oct 9, 2014 at 10:48

Joffrey

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3 Comments

Sambuca Over a year ago

The money variable should not be changed since it is printed out later on.

Joffrey Over a year ago

Indeed, I thought the OP was printing the remaining money, I hadn't read ;-)

user1589375 Over a year ago

This indeed did the trick! Of course I want a new variable to be used :) Thanks to everyone for really fast answers!

Santhosh · Accepted Answer · 2014-10-09 10:48:34Z

0

This condition i <= 0 is never true and probably dont get incremented

i guess its a typo ,

Greater and Lessthan you need to be aware as they change context .

answered Oct 9, 2014 at 10:48

Santhosh

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2 Comments

Evan Knowles Over a year ago

Infinite loop here though.

Santhosh Over a year ago

@Evan oops ! i didnt see to it thanks . feel free to update it to make it clear

Lars Blumberg · Accepted Answer · 2014-10-09 10:55:00Z

0

Your for-loop is not defined correctly. i starts at money = 200. You want to repeat the loop as long as i <= 0. So you require i starting at 200 while not being larger than 0. That's why your loop isn't executed at all.

Instead prefer a while loop for your case. It is more readable:

while (money >= costTogether) {
    money = money - costTogether;
    rounds++;
}

If you want to use a for loop, you can declare it like that:

for (int i = money; i >= costTogether; i -= costTogether) {
    rounds++;
}

edited Oct 9, 2014 at 10:55

answered Oct 9, 2014 at 10:48

Lars Blumberg

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2 Comments

Evan Knowles Over a year ago

He is doing i <= 0?

Lars Blumberg Over a year ago

This is what his code says. Anyway using a for loop does not seem too appropriated for his case.

Evan Knowles · Accepted Answer · 2014-10-09 10:49:36Z

-1

You're only incrementing rounds, in a roundabout way, when the loop runs.

The loop runs while i <= 0 - i starts equal to money, which equals 200, so the loop never runs and the rounds value is not incremented.

You're also not changing i in the loop - I suspect you'd rather want while i >= 0 and decrement i in the loop?

for (int i = money; i >= 0; rounds++) {
    money = money-costTogether;
    i--;
}

answered Oct 9, 2014 at 10:49

Evan Knowles

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1 Comment

Joffrey Over a year ago

This is wrong. i starts at money but is not decremented by the right amount at each turn.

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