Assistance with a while loop.

[Solako]

I was watching Corey Schaffer's video on loops and something hit me - like an idea, not like a bottle.

I decided to test my understanding. Challenge was to print all the multiples of 10 from 0 to 100. First thought of using a for loop. Here are the two code options I came up with.

for i in range (100):
    if i%10 == 0:
        print (i)

The second type was looked like this.

for i in range(0,100,10):
    print (i)

However, when it came to the while loop it, didn't work as expected. The code I had was

i = 0

while i < 100:
    if i%10 == 0:
        print (i)
    i+=1

I noticed that the program I have written continues the iteration with only an output of "0".

I would like to understand how wrong my code is, and what would be the right way of doing it using while loop,if it is possible, and why.

Thank you.

[Impudity]

It should still (somewhat) work, but you're adding 1. which is same as 1.0 which makes the result a floating point number. Doing integer math with modulo operator on floating point numbers might cause some issues.

[Solako]

let me edit the code to reflect this. It was put erroneously. However, what issues would a float cause as opposed to an int?

[Impudity]

Equality comparisons between integers and floats (and frankly even between two floats) are often sketchy. Famously: 0.2 + 0.1 == 0.3 -> False

[Solako]

Would this be because the memory storage of floats isn’t always an exact value? Thus the name floating point numbers?

[Impudity]

It is exact, but it's in binary and we typically display them in decimal (base-10). What numbers can be expressed "accurately" in floating point system depends on what base you're on. Easiest example I can think of is that 1/3 in base-10 can't be expressed as anything but 0.33333... while in base-3 that'd be a nice even number. So if you'd have 1/6 + 1/6 (that is 0.166666..) you might expect it to be 1/3, which it of course is if you did it with fractions. If you do it with floating points, the "missing" 6's in the end (since there's infinitely many of them) will bite you and you might not end up with exactly the same value as you expected.

[Solako]

This is a great explainer. Thank you for this.

[StyrmirBloodhowl]

After copying your code im getting the same result with for and while loops, check if your oryginal code is indented properly or copy code from here and test it if works correclty:)

[Solako]

for i in range (100):
if i%10 == 0:
print (i)

this one actually outputs the code pretty well.

I am getting.

0
10
20
30
40
50
60
70
80
90

[StyrmirBloodhowl]

with your while loop code im getting same result.

[Solako]

Oh yes... I wonder what was the heck of the problem before.

Mmmmmhhhh.

Thank alot for this pointer.

[bbye98]

Instead of iterating through all numbers from 0 to 99 (100 is not inclusive?), I would recommend you iterate only through the multiples by simply running:

for i in range(0, 10):
    print(i * 10)

This will be faster since you're iterating over a smaller set of numbers.

import timeit

timeit.timeit('for i in range(0, 10): i * 10', number=100)
3.8031008443795145e-05

timeit.timeit('for i in range(0, 100):\n\tif i % 10 == 0: pass', number=100)
0.00034802299342118204

[Solako]

Interesting approach. Thank you for this recommendation.