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

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includes label.

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And in this label, we're going to store
number, albeit as a string.

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And we're going to update that label
again, and again, and again.

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So that we ultimately count
down from 50 to zero.

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Glabel, calling it label, gets the
return value of new glabel.

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Now, I'm not going to give this
label value yet, so I'll

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put in quote, unquote.

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>> Next let's call setFont, passing
in the label, and let's pass in

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specifically a font called
SansSerif 36 point.

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A font that happens to exist
inside the CS50 appliance.

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Then finally, let's add the label
to the window as follows.

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Now, let's proceed to induce a
loop that's going to count

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from 50 down to zero.

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And within that loop, let's iteratively
update the label and

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display it on the screen, For, int i
gets 50, i is greater than, or equal

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to zero, i minus, minus.

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>> Now labels, it turns out,
have to be strings.

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But I'm actually counting,
using integers.

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So somehow I'm going to have to convert
the integer, i, to a string

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representation arrow.

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To do so let's declare
char s bracket three.

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So that we have enough storage space
for two digit number, followed by a

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null terminator.

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Then let's call s print f passing
in s, passing in quote,

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unquote percent i.

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Indicating that we indeed want
to format an integer.

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Finally passing in i itself.

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In other words, s print f, or string
print f, just like print f, expects a

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format string followed by some variables
to substitute into that

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format string.

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But it also accepts is its first
argument, the location in which you

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would like to store the string
that you've represented

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with that format string.

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>> So next, let's go ahead and call set,
label, passing in label, passing in s.

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Now, finally, just because this labels
width is going to change over time as

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we count down from 50, to 49, to dot,
dot, dot, to nine to eight.

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Which aren't as wide as
a two digit number is.

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Let's proceed to figure out dynamically
what the width of this

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label should be and then ensure that
it's always centered on the screen.

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I'm first going to declare a double,
calling it x, and I'm then going to

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store inside of x, the result of get
width, passing in the width of the

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whole window, minus get width,
passing in the label.

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Then dividing the whole thing by two.

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Similarly I'm going to declare y to be
equal to get height of the whole

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window, minus get height of just the
label, and divide that by two as well.

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Finally, I'm going to call setlocation,
passing in the label,

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passing in x, passing in y.

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There by positioning the
label at x comma y.

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>> Finally, so that this countdown doesn't
happen too rapidly let's

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pause, for say, 100 milliseconds between
each update of the label.

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To do so, we can call the pause
function, that's defined in the

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Stanford portable library,
quite simply as follows.

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>> Now let's save, compile,
and run this program.

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Make label, dot slash, label.

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There's my user interface
counting down from 50.

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Counting down, and down,
and down, and done.

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