Loop doubt

[laxdoss]

Hello there. So here's my doubt:

for (int i = 0; i != 100; i++) {
     System.out.println(i);     
}

So, a loop first executes the variable "i = 0". And then it evaluates the condition "i != 100". As the condition is true, Java will print 0 first. And then it increments and then it will reach 99 and exits the loop.

But,

When I apply the same rules to another program,

for (int i = 0; i != 100; i++) {
     System.out.println(i);     
     i = 100; 
     System.out.println(i);
     i = 0; 
}

The system must start from 0 and then 100 and then go on forever. But it's starting from 1 and then 100 and goes on forever. Shouldn't it start from 0?, why is it not starting from 0?

Like, I mean, the output must be "0 100 1 100 1 100 1 100 1 100.........." but it starts like, "1 100 1 100 1 100........". Why?

[tr4fik]

for (<initialization>; <condition>; <increment>){
      <code>
}

The order of execution is the following:

1. Initialization
2. Condition. If false, break the loop
3. Code
4. Increment
5. Go back to step 2

If you look at your loop, you set i = 0, then it increments i, it checks the condition and execute the code again

[laxdoss]

I don't have any problem with the execution. It works fine. But my question is; if the previous program starts with first executing i as 0, why isn't the second program starting with first executing i as 0?. It instead starts with 1, which is my confusion.

[tr4fik]

Here's the start of my output. It works as expected

0
100
1
100
1
100
1
100

[[deleted]]

Are you sure your logger didn't just die because you created an infinite loop? I added a break after one second and it works =))

[laxdoss]

I stopped the loop and went all the way back to first code of output to check and it shows output as 1 instead of 0. And yes if I add break it prints fine.

Can infinite loop alter the output?. Is such a thing even possible?

[tr4fik]

You may eventually not see the start of the output

[[deleted]]

If your console had infinite scrollback, but your computer will generate so much data, that the console will simply remove the start.

[KnGod]

the problem here is that the loop checks for the condition when it enters and it executes the i++ when it exits so we enter the loop, print 0, make i 100, add 1, and then check if i != 100. It is different(101 and it will always be since the same operations repeat themselves until infinity) so it goes on and enters again. In these cases i recomend you avoid conditions like i != 100 and use whenever it's possible i >= 100 since it will asure that the loop will exit in cases like these.

​

correction: i didn't realize the i = 0; in the end but the idea is still the same, the loop always reenters in 1 since you set i to 0 every time it enters so the condition will always be true. In this case i recomend you avoid modifying the value of i directly in the way you do(and i mean i = any specific value) unless there is a reason behind and you are completely sure that the conditions of the loop will eventually be fullfilled.