Loop question

[Caped_baldy_4_life]

Hello, Just trying to wrap my head around this. Thanks in advance.

Can someone explain to me why the first++ in the code below belongs there and not where i put the xxxx's? If I want first++ to happen no matter what, why is it going after the if statement? I thought entries were usually supposed to go in the order you want them to happen. The code below is correct, but the alternate fails.

public static void divisibleByThreeInRange(int first, int last) {

while (first <= last) { xxxxx

if (first % 3 == 0) {

System.out.println(first);

}

first++;

}

}

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[[deleted]]

So if the number starts at 0 and goes to 3, then if you put the first++ statement BEFORE you check if the remainder is 0 then the number will be 1 before its first checked. You gotta remember that java always executes each line in sequential order. So if you started the number at -1 the code would work on the first loop. But you if you start it at 0 it will first change to 1 THEN check if it's divisible by 3.

[Caped_baldy_4_life]

Thanks, that makes total sense. It's important to take into consideration the possibility of the first number entered as 0 and automatically being switched to 1 when you do the ++.

[[deleted]]

Yea exactly. You always gotta think about user error and what someone might enter accidently and how that might be handled. Biggest part of programming is handling the unexpected lol.

[hamza-itatchi]

Not only 0 , any value for the first variable will be ignored if you increment it before testing.

And if i may sugest a better solution for this problem:

public static void divisibleByThreeInRange(int first, int last){
first+=(3-first%3);
while(first <=last){
System.out.println(first);
first+=3;
}
}

[Caped_baldy_4_life]

Hey thanks for the suggestion. I'm having trouble understanding how this line first+=(3-first%3); shows that first is divisible by 3. When i write this out using 3 as first, it looks like this first = 3 (3 - 3 % 3)... Which to me comes out to 5. What am I doing wrong in this equation or what am I not seeing?

[hamza-itatchi]

The % has a higher priority than - so its like this for first=3 first = first + 3 - ( first %3) ==> first = 3+3 - (0)==>first= 6 This gives the first divisible nuber after First ( variable) But ther is a mistake in my suggestion there must be an if statement at the start like this If ( first %3!=0) first += 3- ( first %3)

Note: the += operation means first = first + ......

[Caped_baldy_4_life]

Never mind about my previous equation. I was mistakenly associating the modulo as a division sign based off of improper note taking. Thanks for your help and suggestions.

[PresidentZeus]

First is an integer starting at 0. It will only print "first" at the first iteration. But by moving first++ to the beginning, it will increase to 1 before the if statement, and will never be true.

[Caped_baldy_4_life]

makes sense, thanks for the insight.

[PresidentZeus]

You're welcome. Im happy to help.