for loops in java and values of i

Question

In Horstmann's textbook(Big Java Late Objects) on java, for a for loop such as :

for (i = 0; i <= 5; i++)

Horstmann says that values of i for this for loop is 0 1 2 3 4 5 .

However, it seems to me that the value of i should end at 6 since the loop is entered when the i has the value 5 . What am I not understanding about this loops could someone explain me?

(PS. I am sorry if the question is too basic and thus not allowed in this platform.)

edit about the duplicate suggestion: My question is not a duplicate of the suggested link because the suggested link is about the execution of the for loop, mine is about the updating of the variable i , after the end of the execution. I understand that if I would add a System.out.print(i) statement the output will be 0 1 2 3 4 5 because i gets updated after the execution statement (in this case the print statement)

Possible duplicate of [How does a for loop check its conditions in Java?](https://stackoverflow.com/questions/20450056/how-does-a-for-loop-check-its-conditions-in-java) — Johan, Oct 12 '18 at 08:49
Yes, but the accepted answer in the duplicate also states that the update of `i` is executed after the execution of the body (before the termination condition). The author of that question originally asked why the loop printed `i=5` when the condition was set to `i<5` (which was because the author had combined the print statement with the increment part. — Johan, Oct 12 '18 at 09:14
That is a compelling answer, and I am willing to delete this question, due to it being a duplicate. However I also think that I should not because @Roger Lindsjö's answer is more illuminating the ones that were given as an answer to the suggested post. In that case it appears to me as though there is a tie, and I am willing to act in accordance to a tie breaking suggestion . — betaD, Oct 12 '18 at 09:43
I think you should consider this the difference between what is observable (highest value of `i` seen inside the loop body is 5) and what happens 'under the hood' (`i` becomes 6 so the loop terminates) — Mark Rotteveel, Oct 12 '18 at 15:32

score 6 · Accepted Answer · answered Oct 12 '18 at 08:58

You are correct that the value of i will be 6 after the loop has terminated, but perhaps Horstmann meant the values of i inside the loop?

int i;
for (i = 0; i <= 5; i++) {
    System.out.println("Value of i IN loop: " + i);
}
System.out.println("Value of i AFTER loop: " + i);

Output:

Value of i IN loop: 0
Value of i IN loop: 1
Value of i IN loop: 2
Value of i IN loop: 3
Value of i IN loop: 4
Value of i IN loop: 5
Value of i AFTER loop: 6

And it is customary to declare the "counter" for the loop in the loop unless the value when terminating is needed afterwards.

for (int i = 0; i <= 5; i++) {
}
// i is not available here

This makes a lot of sense, afterall it reminded me that the i variable only exists inside the foor loop and "dies" when the loop is no longer executed. — betaD, Oct 12 '18 at 09:11

score 3 · Answer 2 · answered Oct 12 '18 at 08:50

Here is the anatomy of a for loop in Java (similar applies to C/C++ and a few other languages as well)

for (int i=0; i <= 5; ++i)

int i=0     initial condition; happens before the loop starts
i <= 5      check is performed BEFORE each iteration of the loop
++i         loop variable is incremented AFTER each iteration

So, your for loop would iterate 5 times, and at the end of the fifth iteration, i would be incremented to 6. At that point, the i <= 5 check would happen one last time, and it would fail, since 6 is greater than 5.

To convince yourself of all this, run the following Java code:

int i;
for (i=0; i <= 5; ++i) {
    // empty
}
System.out.println(i);

You will see that the value of i after the loop in fact is 6.

This is more detailed answer then mine, Nice job – SamHoque Oct 12 '18 at 08:52 — SamHoque, Oct 12 '18 at 08:52

score 1 · Answer 3 · answered Oct 12 '18 at 08:49

1

This loop

for ( i = 0; i <=5; i ++)

is like

int i = 0;

while (i <= 5){  // Exits when i > 5

   ...

   i++;
} // goes back to while-loop check

answered Oct 12 '18 at 08:49

Saurav Sahu

13,038
6
64
79

score 0 · Answer 4 · answered Oct 12 '18 at 08:50

0

The value of I will end at 5, Because you are doing i <= 5 It checks if I is greater or equal to 5 and then ends the loop. hence making it end at 5 and not 6.

answered Oct 12 '18 at 08:50

SamHoque

2,978
2
13
43

score 0 · Answer 5 · answered Oct 12 '18 at 08:51

Well the man is right! it iterates from 0 to 5, because... 1. the condition is „i <= 5“ 2. Java is 0 indexed, or to be exact by declaring and initialising the variable i = 0, it will start iterating from 0 until the condition returns false. The decisive point here is the conditional pressure inside the for-loop You understand?

score 0 · Answer 6 · answered Oct 12 '18 at 08:52

This is the working sequence with values to see what exactly happens:

i=0 

//tasks

i++ 

i=1 check i<=5 //ok

//tasks

i++

i=2 check i<=5 //ok 
//tasks

i++

i=3 check i<=5 //ok 
//tasks

i++

i=4 check i<=5 //ok 
//tasks

i++

i=5 check i<=5 //ok 
//tasks

i++

i=6 check i<=5 //it's not ok

// exit the loop

score 0 · Answer 7 · answered Oct 12 '18 at 08:53

You are correct that the value of i gets incremented to 6, and then the loop condition does not get satisfied,and the loop exits. However, the author is trying to convey that the values of i for which the for loop block will get executed, are 0, 1, 2, 3, 4, 5.

score 0 · Answer 8 · answered Oct 12 '18 at 08:59

0

The for loop will end in 5 since the condition on your loop is i<=5, meaning the loop will stop if it reaches the number 5.

answered Oct 12 '18 at 08:59

geek_10101010

90
1
4
19

for loops in java and values of i

8 Answers8

Linked