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You use the star for multiplication.
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Let's do one more.
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Printf percent I, divided by percent i, is percent i,
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backslash n. xy divided by y-- so you use the forward slash in C
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to do division.
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And let's do one other.
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Remainder of percent i, divided by percent i, is percent i.
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xy-- and now remainder is what's left over.
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When you try dividing a denominator into a numerator,
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how much is left over that you couldn't divide out?
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>> So there isn't really, necessarily, a symbol
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we've used in grade school for this.
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But there in C. You can say x modulo y, where
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this percent sign in this context-- confusingly when you're inside
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of the double quotes, inside of printf, percent
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is used as the format specifier.
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>> When you use percent outside of that in a mathematical expression,
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it's the modulo operator for modular arithmetic-- for our purposes
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here, just means, what is the remainder of x divided by y?
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So x divided by y is x slash y.
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What's the remainder of x divided by y?
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It's x mod y, as a programmer would say.
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>> So if I made no mistakes here, let me go ahead and make ints, plural, nice,
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and dot slash ints.
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And let's go ahead and do, let's say, 1, 10.
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All right, 1 plus 10 is 11, check.
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1 minus 10 is negative 9, check.
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>> 1 times 10 is 10, check.
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1 divided by 10 is-- OK, we'll skip that one.
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Remainder of 1 divided by 10 is 1.
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That's correct.
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But there's a bug in here.
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>> So the one I put my hand over, not correct.
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I mean, it's close to 0.
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1 divided by 10, you know, if we're cutting some corners, sure, it's zero.
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But it should really be 1/10, 0.1, or 0.10, 0.1000, or so forth.
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>> It should not really be zero.
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Well, it turns out that the computer is doing literally what we told it to do.
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We are doing math like x divided by y.
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And both x and y, per the lines of code earlier, are integers.
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>> Moreover, on line 15, we are telling printf, hey, printf plug-in
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an integer, plug-in an integer, plug-in an integer-- specifically
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x, and then y, and then x divided by y. x and y are ints.
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We're good there.
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>> But what is x divided by x?
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x divided by y should be, mathematically, 1/10, or 0.1,
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which is a real number, a real number having, potentially, a decimal point.
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It's not an integer.
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>> But what is the closest integer to 1/10, or 0.1?
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Yeah, it kind of is zero.
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0.1 is like this much.
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And 1 is this much.
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So 1/10 is closer to 0 than it is to one.
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>> And so what C is doing for us-- kind of because we told it to--
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is truncating that integer.
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It's taking the value, which again is supposed to be something like 0.1000,
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0 and so forth.
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And it's truncating everything after the decimal point
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so that all of this stuff, because it doesn't
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fit in the notion of an integer, which is just a number like negative 1, 0, 1,
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up and down, it throws away everything after the decimal point because you
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can't fit a decimal point in an integer by definition.
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>> So the answer here is zero.
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So how do we fix this?
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We need another solution all together.
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And we can do this, as follows.
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>> Let me go ahead and create a new file, this one called floats.c.
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And save it here in the same directory, float.c.
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And let me go ahead and copy some of that code from earlier.
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>> But instead of getting an int, let's do this.
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Give me a floating point value called x. where a floating point
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value is just literally something with a floating point.
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It can move to the left, to the right.
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It's a real number.
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>> And let me call not get int, but get float,
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which also was among the menu of options in the C250 library.
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Let's change y to a float.
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So this becomes get float.
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>> And now, we don't want to plug in ints.
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It turns out we have to use percent f for float, percent f for float,
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and now save it.
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And now, fingers crossed, make floats, nice, dot slash floats.
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x is going to be one 1. y Is going to be 10 again.
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>> And, nice, OK my addition is correct.
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I was hoping for more, but I forgot to write it.
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So let's go and fix this logical error.
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>> Let's go ahead and grab the following.
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We'll just do a little copy and paste.
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And I'm going to say minus.
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>> And I'm going to say times.
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And I'm going to say divided.
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And I'm not going to do modulo, which is not as germane here,
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divided by f, and times plus-- OK, let's do this again.
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>> Make floats, dot slash floats, and 1, 10, and-- nice, no, OK.
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So I'm an idiot.
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So this is very common in computer science
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to make stupid mistakes like this.
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>> For pedagogical purposes, what I really wanted to do
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was change the science here to plus, to minus, to times,
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and to divide, as you hopefully noticed during this exercise.
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