Value of Fortran DO loop index after the loop

Question

How do DO loops work exactly?

Let's say you have the following loop:

do i=1,10
...code...
end do

write(*,*)I

why is the printed I 11, and not 10?

But when the loop stops due to an

if(something) exit

the I is as expected (for example i=7, exit because some other value reached it's limit).

Answer 1

The value of i goes to 11 before the do loop determines that it must terminate. The value of 11 is the first value of i which causes the end condition of 1..10 to fail. So when the loop is done, the value of i is 11.

Put into pseudo-code form:

1) i <- 1
2) if i > 10 goto 6
3) ...code...
4) i <- i + 1
5) goto 2
6) print i

When it gets to step 6, the value of i is 11. When you put in your if statement, it becomes:

1) i <- 1
2) if i > 10 goto 7
3) ...code...
4) if i = 7 goto 7
5) i <- i + 1
6) goto 2
7) print i

So clearly i will be 7 in this case.