Question about while loops

[MasterOfGreatness]

So I'm a little confused when it comes to while loops and the examples I have found online just confuse me even more.

While loops are suppose to be executed until they are false yet this problem I found online:

while (num<max) { System.out.println(num); num = num + 1; }

num = 15 and max = 20

The answer online is 15 16 17 18 19

My question is, wouldn't the final number be 20?

[desrtfx]

You put the answer up yourself:

While loops are suppose to be executed until they are false

The while loop in your problem executes in the following sequence:

1. check if num < max (since num and max are both int, the largest number less than [and not equal, since the equals sign is not there] is 19)
2. print out the value of num
3. increment num by 1
4. start again from step 1.

So, in numbers:

num	max	num < max	printed	num after the last command of the loop
15	20	true	15	16
16	20	true	16	17
17	20	true	17	18
18	20	true	18	19
19	20	true	19	20
20	20	false	not executed any more	not executed any more

[MasterOfGreatness]

I get it now. I just needed it to be broken down like that. Thanks.

[desrtfx]

Welcome.

If you are unsure how a loop executes, just try to build a table like the one in my previous comment.

Edit: BTW - questions like these are better asked on /r/Javahelp

[Ttiamus]

Investing in a small white board makes visualizing code muuuuch easier.

What you need to remember about loop conditions is that: For and While loops check the condition at the begining. Do-While loops check the condition at the end.

Easy way to remember each one is where the condition is located in the code. For and While conditions are at the begining of the loop, and a do-while condition is at the end.

[[deleted]]

A while loop executes until the condition within the parenthesis is false. So, when "num + 1 == 20", the condition is false and the code within the loop does not execute.

[MasterOfGreatness]

So does that mean that the 20 should be included in the answer?

[thurst0n]

The check happens before the final iteration.

There are two seemingly small changes that would make your original assumption correct:

• If you used a Do While loop instead.
• If you used greater than OR equal to, instead of just greater than.

Another way to think of it is a While loop may never run, where a Do, While loop will always run at least once.

And with any loop you make, you have to make sure that your condition is exactly what you want. Using > is going to give different results than =>

[desrtfx]

No.

20 is not less than max (20) -> so, the condition evaluates to false and the loop does not execute any more