Name: データ型 (Data Types)
Uploaded: 2021-01-14T10:41:47.000Z
Duration: 13 min 42 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

So let's talk about another thing that's kind of unique to C,

When I say unique to C, I really only mean in the context of,

if you've been a programmer for a really long time,

you've probably not worked with data types

if you've used modern programming languages.

Modern languages like PHP and JavaScript,

which we'll also see a little later on in the course,

you don't actually have to specify the data type of a variable

>> You just declare it and start using it.

If it's an integer, it know it's an integer.

If it's a character, it's knows it's a character.

If it's a word, it knows it's a string, so-called.

>> But in C, which is an older language, we need

to specify the data type of every variable

that we create the first time that we use that variable.

So C comes with some built-in data types.

And let's get familiar with some of those.

And then afterwards we'll also talk a little bit about some of the data types

that we've written for you, so you can use them in CS50.

The int data type is used for variables that will store integer values.

Integers, which is something you should keep in mind for the quiz,

always take up four bytes of memory, which is 32 bits.

>> So this means that the range of values that an integer can store

is limited by what can fit within 32 bits worth of information.

Now as it turns out, it was long ago decided

that we would split up that range of 32 bits

into negative integers and positive integers,

So the range of values that we represent with an integer range from negative 2

to the 31st power to 2 to the 31st power minus 1,

>> So basically half of the possible values you can fit in an int are negative,

And roughly here, this is about negative 2 billion to about positive 2 billion.

So that's what you can fit in an integer variable.

Now we also have something called an unsigned integer.

Now unsigned ints are not a separate type of variable.

Rather, unsigned is what's called a qualifier.

It modifies the data type of integer slightly.

>> And in this case, what unsigned means-- and you can also

use unsigned other data types, integer's not the only one.

What it effectively does is doubles the positive range of values

that an integer can take on at the expense of no longer allowing

So if you have numbers that you know will get higher than 2 billion but less

than 4 billion, for example-- which is 2 to the 32nd power--

you might want to use an unsigned int if you

>> You'll occasionally have used for unsigned variables

But again, the range of values that you can represent with an unsigned integer

as to t regular integer, are 0 to 2 to the 32nd power minus 1,

So you've effectively doubled the positive range that you can fit,

but you've given up all the negative values.

>> Now as an aside, unsigned is not the only qualifier

that we might see for variable data types.

There are also things called short and long and const.

Const we'll see a little bit later in the course.

>> But just know that there are other qualifiers.

But it's the only one we're going to talk about right now.

So chars are used for variables that will store single characters.

And sometimes you might hear people pronounce it as car.

>> So characters always take up one byte of memory, which is just 8 bits.

So this means that they can only fit values in the range of negative 2

to the seventh power, or negative 128, to 2 to the 7th power minus 1, or 127.

>> Thanks to ASCII, it was long ago decided a way

to map those positive numbers from 0 to 127 to various characters

So as we'll see later on in the course, and you'll probably

come to memorize at some point, capital A, for example--

the character capital A-- maps to the number 65.

And the reason for that is because that's what's it's

The character 0 for when you actually type the character, not

You'll learn a couple of these as you go.

And you'll certainly come to need them a little bit later in CS50.

>> The next major data type is floating point numbers.

So floating point numbers are also known as real numbers.

They're basically numbers that have a decimal point in them.

Floating point values like integers are also

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データ型 (Data Types)

weird

basically

positive

negative