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SPEAKER 1:Let's write a program with a
graphical user interface that includes

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a window and a button there in.

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Let's get started.

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>> First, let me go ahead and declare a g
window, calling the variable window.

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And assign to it, the return
value of new g window.

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Which will instantiate our window.

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And then we specify a width of 320
pixels, and the height of 240 pixel.

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Somewhat arbitrarily, but small
enough to fit on the screen.

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Let's now instantiate a g button.

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Not only with a label that the user
will see, but also with a unique

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identifier.

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A so-called action command, that will
indeed uniquely identify that button.

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g button, button, gets the return
value of new g button.

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And it's a label shall be,
quite simply, button.

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And then let's set action command,
passing in that button and a unique,

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and some what arbitrary word, click.

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Let's now add the button to a region
of the window, bypassing in window,

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and the button, and an identifier for
the southern region of the window--

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that according to the Stanford portable
library, is the lower portion

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of the screen.

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>> And now let's deliberately
induce an infinite loop.

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Inside of this loop we're going
to listen for two things.

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One, whether the user has chosen
to close the window.

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And two, whether or not the user has
clicked on that specific button.

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First, we're going to declare
a g action event, calling

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the variable event.

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And assign to it, the return value
of wait for event, action event.

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>> And now let's check if that event
is the closing of a window.

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If, get, event, type, passing an
event, equals, equals, window

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underscore closed.

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A special constant declared in the
Stanford portable library that

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represents exactly that, the
closing of a window.

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Then I'm going to break out of this
otherwise infinite loop, so that we

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reach the end of the function.

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Otherwise, I'm going to check if
string compare of get, action,

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command, passing an event, comma, quote
unquote, click-- that unique

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identifier from before--

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equals, equals, zero.

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Then, I'm going to print out something
arbitrary, like button was clicked.

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>> In other words, if upon hearing that a
button was clicked, and that event

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indicates that the button was clicked
was the one with the unique identifier

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of quote unquote click, then I want
to report as much on the screen.

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Now in this case, I only
have one button.

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But just in case my application had
multiple buttons, this technique would

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allow me to distinguish among
those several buttons.

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Outside of this loop, now, I'm going to
proceed to close g window, passing

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in window as its argument,
and then return zero.

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>> Let's now save, compile,
and run this program.

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Make button, dot slash button.

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There's my window, there's the button.

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Let's go ahead and click
on the button.

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And the button was clicked.

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Let's click on that again.

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Button was clicked.

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>> Let's now click on the x in the top
right hand corner to close the window,

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and we break out of that loop
and we return zero.

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