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So there are two kinds of
loops you can use in Python.

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The for loop, which you just
discovered here in the previous lesson,

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and the while loop, which
we are going to see now.

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And you will see that the
knowledge you got when working

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on conditional statements
will be very useful here.

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To explain how while loops work,

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I'm first going to do the exact
same thing as for the loop here.

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So we are going to
print hello with a counter.

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But this time using while,
just going to put back to 10,

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because that's going
to be a simpler to read.

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So just follow along and
I'm going to explain that.

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I'm going to create first
a variable i is equal to 0.

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And then I'm going to do while i is
lower than 10, strictly lower than 10.

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I put a colon and then I do print hello.

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And then plus str i.

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Okay, so let's bring the same
thing and I do i plus equal 1.

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Let's actually comment those two lines.

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Okay, so you can see
I just comment like this.

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So those will not be executed.

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I'm running the programs and you can
see we have hello zero until hello nine.

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So this is the exact
same behavior with this

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and with this we have
the same behavior.

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So now how does it work?

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Well, the while loop is
different here because

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with the while you are going to test
here, this is a conditional statement.

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Okay, so the while loop is
basically the same as if structure.

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The difference is that
while this condition is true,

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this block of code will
continue to be executed.

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Okay, so you check if that is true.

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If it's true, yes, then you execute this.

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You come back to line five.

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You check again if this is true.

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If yes, you continue to execute this, etc.

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etc.

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And then when we come back to the
line five and if this condition is false,

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in that case, we don't
enter the block of code

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and re-resume the
program here at line eight.

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So what did I do here?

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I created first a variable i that
we're going to use as a counter.

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Now I'm going to check while i is strictly
lower than 10, we continue to execute this.

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So at first, i is equal to zero.

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So i is... So zero is lower than
10, yes, we print hello plus zero.

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And then what I'm
going to do, I need to do

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that, I'm going to add
one to the counter, okay?

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So I'm going to add one every time.

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To add one, so you can actually
do i is equal to i plus one, okay?

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But there is a shortcut,
you can do plus equal.

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And this is simply going to add the element
on the right to the variable on the left.

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So now i is equal to one,
I come back to line five.

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One is strictly lower than
10, yes, we print hello one.

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And then I put plus one, so
i is not equal to two, etc. etc.

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At one point, i will be equal to nine.

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So nine is lower, strictly
lower than 10, yes.

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We print hello nine, I do nine plus one.

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So we get 10, no, i is equal to 10.

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We come back to line five and
then is 10 strictly lower than 10?

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No, this is false.

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So we stop the while loop.

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Okay, and the condition here for the
while can be anything you want, okay?

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Here, this is a very classic
example with a counter.

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But as an example, let's say you read
the temperature of your computer, okay?

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And you want to continue
doing an action while

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the temperature is lower
than the threshold, okay?

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You continue, you continue, and then
you continue to read also the temperature.

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And when the temperature
starts to get above the threshold

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that you have set, then you
stop executing the while loop.

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All right, and now the
one million dollar question.

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When to use a for loop versus
when to use a while loop?

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So basically, use a for
loop when you know exactly

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how many times you
want to execute an action.

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Use a while loop when you
don't know how many times,

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or for example, if the condition
to continue is external to the loop.

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As an example, let's say you want to
ask a user to give you some numbers.

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In the first scenario, you
want exactly 10 numbers.

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So you are going to use a
for loop and ask 10 times.

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In the second scenario, you allow the
user to give as many numbers as they want,

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and you stop asking whenever
the user gives you the number zero.

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Here, you are going to use a while loop.

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And don't worry if you still
have some confusion about this.

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In many cases, both
options are actually possible,

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just with a different
way of writing the code.

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With a bit of experience, the choice
will become much easier for you.

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And lastly, if we come back to the example
here, the exact example I've used here,

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you can see that, well, here the for
loop was actually more appropriate,

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because we knew exactly how
many times we wanted to print the text.