Hello world! I'm talking about do loops in C#.

I have the same program with the list box.

And I want to add 1, 2, 3 to that list box.

This time I'm going to use a do loop.

A very important difference between for and while and do loops is...

that

for and while loops

will execute zero.

or more times.

A do Loop has the test

at the end:

Therefore a do loop always executes

at least once.

This is typically used in situations where

Maybe the user has to enter a value, and it has to be valid within some range and so you would...

use this loop:

Get the input, and if the input is not valid we tell them they have to do it over again.

For instance entering a password: maybe we give them three tries to do that.

This is just going to add 1, 2, 3 to the list box.

I start off with num is 0.

You notice it just says do, no parentheses, and then we just have

the body of the loop between the curly braces.

We add

1 to num.

And it becomes one.

And 1 is added to the list box.

1 is less than 3,

So we're going to do the entire body again.

Let's just jump

to where num became three right here: num became 3.

3 was added to the list box,

num is less than 3

Is no longer true.

And we just drop down to whatever statement is next after the body of the loop.

And that's it.