Hello world!
I'm talking about writing a function in C#.
I have started a new program called circle.
I have lblInstructions
that says "Enter the radus of a circle.
I have txtRadius,
I have btnSubmit,
I have a label called area header
that says "The area is "
And then there's another label here that you can't see.
So I'm going to select it this way.
It doesn't have any text right now,
but it is called lblRadius [it should be lblArea]
I want the user to be able to type and then press enter.
So I'm going to go to my form,
and for the accept button select btnSubmit.
And then,  let's double click on the submit button
and we're going to, first of all we're going to
declare a string s
equal to txtRadius.Text
And then we're going to have a ...
double radius equals zero.
and then I'm going to say Double.TryParse
and the string that I want to convert
and the output is radius.
And then I would like to calculate the area.
But I'm going to write a function for this.
So we start by saying private
and then instead of void,
this is going to return a double.
to and the name is going to be
area of circle.
and it is going to have the parameter is a double
and the parameter is going to be, let's call it r.
And those curly braces
And the area of a circle
is PI r squared.
And I'm going to say return
Math.PI
times r
Now, I could use Pow(r,2)
But I think I'm just going to use r times r.
It's just a little bit easier, I think, to understand.
What we've got here: now that we have that function,
I'm going to say
lblArea...
Oh, I called it radius, oh, let's just do this.
lblRadius.Text equals
area of the circle, sending it radius,
and then were going to convert that to a string.
Uh... function and the semicolons, let's just run this.
And I'm going to put in five
and hit submit.
And it says 78 point something.
And we can just do this in our head:
We had PI which is about three,
and 3󬊅
is about 75, but it's a little more that because it's not exactly 3.
And so that's it. We wrote our own function.
Now I challenge you:
do this for the circumference.