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Equality Comparisons - Intro to Computer Science

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    Everything we've done so far has been pretty limited,
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    that we had to do the same thing on all data.
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    We couldn't do anything that really depended on what the data was.
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    What we're going to do next is figure out a way to make code behave differently
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    based on decisions.
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    The first thing we're going to do is figure out some ways to make comparisons,
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    so we have a way to test and decide what we should do.
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    Python provides lots of different operators for doing comparisons.
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    There are things similar to what we've used in math.
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    We have a less than sign that compares 2 numbers.
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    We have the greater than.
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    We have a less than or equal to. Things like this...
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    All of these operate on numbers, so we can have a number followed by
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    a comparison operator, followed by another number.
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    This is very similar to the grammar we saw earlier for arithmetic expressions,
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    but now instead of having a plus or times here,
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    we can have something that does a comparison.
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    The output of a comparison though is not a number.
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    It's a Boolean value, and a Boolean value is 1 of 2 things.
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    It's either the value True or the value False.
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    Let's see some examples in the Python interpreter.
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    First, we'll use the less than to compare 2 and 3.
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    So 2 is less than 3, so we expect the result to be true.
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    When we run this, we see that the result is true.
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    If we compare a number greater than 3, let's say 21 < 3.
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    The result will be false.
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    We can have any expression we want with a comparison,
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    so we can do 7 * 3 < 21.
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    When we run that, we also get false because 7 x 3 = 21,
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    which is not less than 21.
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    Another comparison operator we can use is not equal to.
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    So != means not equal to.
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    So 7 * 3 != 21 is false because 7 x 3 is equal to 21.
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    If we want to do equality comparison, we don't use the equal sign,
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    we use 2 equal signs.
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    We call that the double equal.
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    So now we have 7 * 3 == 21, and the result there is true.
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    Now we're going to have a quiz to see if you can figure out why we need to use
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    the == here instead of just the single =.
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    The question is, why is the equality comparison done using ==,
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    having 2 equals, instead of just a single = sign?
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    The possible answers: Because = means approximately equal,
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    and we want to do exact equality comparisons.
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    Because we needed to use 2 characters for the not equal comparison,
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    and we wanted the equal to be the same length.
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    Because Guido, the designer of Python, really likes = signs.
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    Because the single = sign means assignment,
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    or it doesn't really matter. We can use either == or =.
Title:
Equality Comparisons - Intro to Computer Science
Description:

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Video Language:
English
Team:
Udacity
Project:
CS101 - Intro to Computer Science
Duration:
02:50

English subtitles

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