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>> It's not all that inspiring.
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And, indeed, these first few examples will take some time
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to ramp up in excitement.
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But we have so much more control now, in fact.
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And we're going to very quickly start layering
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on top of these basic primitives.
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>> But first, let's understand what the limitations are.
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In fact, one of the things Scratch doesn't easily
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let us do is really look underneath the hood,
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and understand what a computer is, what it can do,
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and what its limitations are.
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And, indeed, that lack of understanding, potentially, long-term
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can lead to our own mistakes-- writing bugs, writing insecure software that
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gets hacked in some way.
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>> So let's take some steps toward understanding this a little better by
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way of, say, the following example.
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I'm going to go ahead and implement real quick a program called Adder.
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Like, let's add some numbers together.
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And I'm going to code some corners here, and just copy and paste
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where I was before, just so we can get going sooner.
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So now I've got the basic beginnings of a program called Adder.
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>> And let's go ahead and do this.
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I'm going to go ahead and say, intx gets get int.
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And you know what?
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Let's make a better user experience.
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>> So let's just say x is, and effectively prompt the user to give us x.
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And then let me go ahead and say, printf how about y is, this time expecting
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two values from the user.
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And then let's just go ahead and say, printf, the sum of x and y is.
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And now I don't want to do percent s.
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I want to do percent i, backslash n, and then plug in sum value.
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>> So how can I go about doing this?
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You know what?
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I know how to use variables.
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Let me just declare a new one, int z.
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>> And I'm going to take a guess here.
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If there are equal signs in this language, maybe I can just do x plus y,
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so long as I end my thought with a semi-colon?
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Now I can go back down here, plug in z, finish this thought with a semi-colon.
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And let's see now, if these sequences of lines-- x is get int.
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Y is get int.
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>> Add x and y, store the value in z-- so, again, remember the equal sign
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is not equal.
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It's assignment from right to left.
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And let's print out that the sum of x and y is not literally z,
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but what's inside of z.
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So let's make Adder -- nice, no mistakes this time.
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Dot slash Adder, enter, x is going to be 1.
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>> Y is going to be 2.
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And the sum of x and y is 3.
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So that's all fine and good.
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>> So you would imagine that math should work in a program like this.
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But you know what?
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Is this variable, line 12, even necessary?
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You don't need to get in the habit of just storing things in variables
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just because you can.
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And, in fact, it's generally considered bad design
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if you are creating a variable, called z in this case, storing something in it,
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and then immediately using it, but never again.
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Why give something a name like z if you're literally
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going to use that thing only once, and so
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proximal to where you created it in the first place,
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so close in terms of lines of code?
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So you know what?
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It turns out that C is pretty flexible.
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If I actually want to plug-in values here,
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I don't need to declare a new variable.
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I could just plug-in x plus y, because C understands
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arithmetic, and mathematical operators.
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>> So I can simply say, do this math, x plus y, whatever those values are,
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plug the resulting integer into that string.
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So this might be, though only one line shorter,
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a better design, a better program, because there's less code, therefore
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less for me to understand.
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And it's also just cleaner, insofar as we're not
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introducing new words, new symbols, like z,
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even though they don't really serve much of a purpose.
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>> Unfortunately, math isn't all that reliable sometimes.
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Let's go ahead and do this.
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I'm going to go ahead now and do the following.
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>> Let's do printf, percent i, plus percent i, shall be percent i, backslash n.
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And I'm going to do this-- xyx plus y.
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So I'm just going to rewrite this slightly differently here.
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Let me just do a quick sanity check.
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Again, let's not get ahead of ourselves.
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Make adder, dot slash adder.
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x is 1, y is 2, 1 plus 2 is 3.
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So that's good.
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But let's complicate this now a bit, and create a new file.
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>> I'm going to call this one, say, ints, plural for integers.
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Let me start where I was a moment ago.
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But now let's do a few other lines.
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Let me go ahead and do the following, printf, percent i, minus percent i,
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is percent i, comma x, comma yx minus y.
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So I'm doing slightly different math there.
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Let's do another one.
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So percent i times percent i is percent i, backslash n.
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Let's plug-in x, and y, and x times y.
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We'll use the asterisk on your computer for times.
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>> You don't use x. x is a variable name here.
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