Python redundancy

Question

If I have the code

i = 0
while i < N:
    print("Hello")
    i += 1

how many times will Hello be printed out? (assume that N is a defined integer)

Answers:

0
N
N-1
N+1
more than N+1

and why? I never get this so I would appreciate of somebody could explain.

It would be printed N times. i starts at 0. Your condition demands that the loop exit if i is not less then N. But because your index starts at 0, it will be printed exactly N times. Try replacing "Hello" with the variable i. I think that will put things in perspective. — Gabriel Samfira, Jul 06 '13 at 20:49
Have you tried to work it out starting from your understanding of the `while` loop? — user4815162342, Jul 06 '13 at 20:49
Relax lol, everyone has to start off somewhere. In time loops will become second nature, and don't be disheartened by any nasty comments. They come from people who have forgotten that they once had to get their head around this. — Adrian Trainor, Jul 06 '13 at 21:06

arshajii · Answer 1 · 2013-07-06T20:53:59.757

5

The best way to figure it out is to go through it by hand for a few manageable values of N. For instance, if N is 2:

i == 0 and 0 < 2 → print "hello", increment i
i == 1 and 1 < 2 → print "hello", increment i
i == 2 and ~~2 < 2~~ → while-loop condition is no longer satisfied → loop ends

So for N = 2, "hello" is printed 2 times. See the pattern?

edited Jul 06 '13 at 20:53

answered Jul 06 '13 at 20:48

arshajii

127,459
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score 2 · Accepted Answer · edited Jul 06 '13 at 21:56

2

Hello will be printed out N times. assume N is 3.

1st iteration i = 0 i is less than N

print hello
i = i + 1; // i = 1

2nd iteration i = 1; i` is less thanN (3)`

print hello
i = i + 1; // i = 2

3rd iteration i = 2; i is less than N (3)

print hello
i = i + 1; // i = 3

4th iteration i = 3; i is equal to N (3) break loop

edited Jul 06 '13 at 21:56

answered Jul 06 '13 at 20:49

Adrian Trainor

267
1
9

This make sense for me, how would your example be with N+1? – Eri. Jul 06 '13 at 20:55
It wouldn't, because N+1 is not the answer... – JcKelley Jul 06 '13 at 20:56
2

N+1 (given the example above) would be N = 4, so it would print hello 4 times – Adrian Trainor Jul 06 '13 at 20:59

score 2 · Answer 3 · answered Jul 06 '13 at 20:53

As the other answers described, it would print N times, because it starts at 0 and goes until it is just before N, not equal to N.

In reality, though, this is very redundant in Python. A much easier way to do this, making it a bit more readable (and hopefully easier for you to understand):

N=3
for x in range(0,N):
    print "This is loop %d" % (x)

This loop will print from 0 to N, which is really just N amount of times.

Python redundancy

3 Answers3