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>> SPEAKER 1: Let's write a program that
prompts the user for the names and

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houses of three students.

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Now, to store those names and houses
we could use, what, six variables.

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Three strings for the names, and another
three strings for the houses,

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but we already know that we can clean up
that code by using arrays instead,

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for instance an array of size 3 for the
three names, and another array of

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size 3 for the houses.

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But it turns out we can clean this up
further still, and actually keep those

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names and houses together, so that a
student's name and his or her house

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are somehow encapsulated, so to
speak, into the same variable.

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>> To do this, though, we need to declare
our own data type, our own type in C,

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that the authors of C didn't necessarily
think of years ago.

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To do this we can use the keyword
typedef, along with the

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other keyword struct.

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Let's take a look.

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Inside of structs.h, I've already
gotten started by

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including the CS50 library.

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I'm next going to type typedef struct,
and then a curly brace.

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Inside of the struct, I'm going to
specify that a student shall have a

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string called name, and another
string called house.

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I'm going to then close my curly braces,
and specify that the name of

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this new data type shall be student.

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In other words, via this syntax have I
declared a new data type of my own

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that didn't exist a moment ago, and
inside of this data type are two data

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fields or data members, one called name,
one called house, both of which

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are of type string.

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>> Let's now use this type
in an actual program.

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In structs0.c, I've similarly gotten
myself started already with some

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boilerplate code, and I'm now
going to use this data

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type student, as follows.

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I'm first going to declare an
array of type student, I'll

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call the array students--

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plural--

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and I'll specify that its size will be
three, which, notice, is the value of

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the constant STUDENTS--

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in all capitals--

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that I've declared up here,
earlier in the file.

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Let's now iterate over those three
students, and prompt the user for

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their names and houses.

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>> for int i get 0, i is less
than that constant, i++.

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And now inside of the body of this for
loop, I'm going to print out something

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like student's name.

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I'm then going to actually get that
student's name by specifying

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students bracket i.

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In other words I want the i-th student
in the array called students, but now

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I want to get at that i-th student's
name, and to do this, I'm going to use

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the . operator, in order to get at a
specific field inside of the struct.

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So I specify students bracket i .name
gets the return value of GetString().

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Meanwhile, I'm going to print out
something similar, saying student's

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house, and now I'm going to specify
that the i-th students house field

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shall get the return value of
another call to GetString().

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>> Now let's do something with these three
students' names and houses,

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something simple like printing
each out in a sentence.

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for int i get 0, again i is less than
students, i++, printf "%s is in %s .

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backslash n", and now let me plug in
the values of those two fields,

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students bracket i .name, comma,
students bracket i .house, close

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paren, semicolon.

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>> And now I need to do one more thing.

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At the bottom of this file, I need to
free the memory that was allocated

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behind the scenes by GetSring(), which
of course calls malloc, in order to

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allocate memory for the strings
the user types.

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But this to is simple.

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for int i get 0, i is less than
students, i++, and inside the body of

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this for loop, I'm simply going to
provide free students bracket i .name,

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and free students bracket i .house.

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>> Now, we've clearly used three for loops
in this program, when really I

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could have just used one, but this is
just for demonstration's sake, so that

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we can specify in three distinct
steps what exactly we're doing.

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We're first getting a name and a house
for each of the students, we're then

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printing out the name and the house for
each of the three students, and

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then we're going to free the memory
used by each of the students.

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But surely we could've combine this
into one bigger for loop.

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>> Let's now save, compile,
and run this program.

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make structs 0 ./structs 0, student's
name, let's provide David, he'll live

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in Mather House, student's name, let's
say Lauren, she'll live in Leverett

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House, student's name, Rob, he'll
live in Kirkland House.

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And indeed, David is in Mather,
Lauren is in Leverett,

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and Rob is in Kirkland.

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