Am i wrong or the result is wrong?

Question

I have a java example, I know it's very easy, but I'm just a beginner. I have a problem in line 8 and 9:

while (tailFeathers > 1){
System.out.print(--tailFeathers + " ");}

I think it will print "5 2" because 1 is not greater than 1, but the answer is E, which is "5 2 1". Could u explain to me? Am I wrong or strange result? Thanks so much.

Please paste the code and results into the question as text. It is very difficult to read as an image. — NomadMaker, Oct 08 '20 at 15:40
if tailFeathers is 2, 2 > 1, and because of --tailFeathers it will print 1. — Joop Eggen, Oct 08 '20 at 15:40
See https://stackoverflow.com/questions/2371118/how-do-the-post-increment-i-and-pre-increment-i-operators-work-in-java — Federico klez Culloca, Oct 08 '20 at 15:40
I'd have guessed it was G - fails on line 6. I'm trying to find whyyou can have a `case` inside a `default`... and it's not a label, unless the space between `case` and `3` is secretly not a space at all. — S.L. Barth, Oct 08 '20 at 15:47
@S.L.Barth-ReinstateMonica that's not a case inside a default, it's a case (`default`) followed by another case (`case 3`). That's the reason you need `break`s between `case`s. — Federico klez Culloca, Oct 08 '20 at 15:49
@FedericoklezCulloca Ah, thanks! That makes sense. Pretty messed up piece of code, with (among others) `default` coming before another `case`. If this is for an interview, I hope the REAL test is to see if the prospective developer is revolted by the snippet :-) — S.L. Barth, Oct 08 '20 at 15:53

score 3 · Answer 1 · edited Oct 08 '20 at 15:52

Follow the logic closely

It seems you agree that that at line 7. The output to the screen is "5 "

At this point tailFeathers = 3

3>1 so enter the loop, decrement tailFeathers before using it.

So the screen output is now "5 2 "

At this point tailFeathers = 2

2>1 so enter the loop, decrement tailFeathers before using it.

So the screen output is now "5 2 1"

at this point tailFeathers = 1

1=1 don't enter the loop

screen output is "5 2 1"

Solomon Slow · Answer 2 · 2020-10-08T15:59:05.743

I think it will print "5 2" because 1 is not greater than 1, but the answer is E, which is "5 2 1". Could u explain to me?

You are correct in thinking that the loop body will not be entered when tailFeathers==1, but you misunderstand what will be printed.

Here's the loop:

while (tailFeathers > 1) {
     system.out.print(--tailFeathers + " ");
}

Let's suppose that the loop body was entered because tailFeathers==2 which is > 1. The system.out.print(--tailFeathers + " ") statement will do several things in a well defined order:

It will decrement the value of tailFeathers (i.e., it will set tailFeathers=1),
It will call library functions to create a new String, "1", to express the new, decimal value of tailFeathers,
It will concatenate the string "1" with the string " " to create a new string, "1 ", and then finally,
It will call system.out.print("1 ").

The key concept here is the meaning of --tailFeathers. The value of that expression is the value of tailFeathers after the variable has been decremented.

If you changed it to tailFeathers--, you'd get a different result. In that case, the value of the expression is the value that tailFeathers had before it was decremented (i.e., 2 in my example, above.)

The way to remember this is to read it from left to right:

--t means first, decrement t, then use the new value of t, and
t-- means first, use the original value of t, and then some time later, decrement t.

score 0 · Answer 3 · answered Oct 08 '20 at 15:55

0

--counter => counter = counter-1. Its value gets updated instantly and this is how the the pre operator works. Also, remember there is while loop in the last, so it prints recursively until the condition becomes false.

answered Oct 08 '20 at 15:55

Dinesh Kumar

1

Am i wrong or the result is wrong?

3 Answers3