Why create structs this way?

So i been studying C, and got to structs and saw this example online:

Code:

#define MAX_DATA 512
#define MAX_ROWS 100

struct Address {
int id;
int set;
char name[MAX_DATA];
char email[MAX_DATA];
};

struct Database {
struct Address rows[MAX_ROWS];
};

struct Connection {
FILE *file;
struct Database *db;
};

My question is why do people create structs that contain others?

I understand Address, now Database it has inside struct Address rows[MAX-ROWS], this means that its creating an array that contains id,set,name,email and this values are stored in the array in that way

id | set | name | email < ROW#1 (and it has a max of 100 rows)

Ten Connection includes this array(rows) and a file name

correct??

Database includes an array of struct Address.The size of the array is MAX_ROWS.So every cell of the array has a struct Address stored in it,thus every cell contains an id,set,name and email.So DataBase contains an array of MAX_ROWS Address(es).
Connection has a pointer to FILE and a pointer to struct Database

Maybe this type of coding was elegant for these example

It should be aligned with how you are looking at the data you're dealing with. Take a student for example. Each student will have classes, a GPA, a major, a student number for an ID, a first and last name (at least), etc. So it's natural to include all the above data, with the student struct.

How you intuitively think about the data, is a good place to start with organizing structs, and structs inside other structs, too.

Try to keep it simple, though. Did you see your error in the above code description? It's so easy to change MAX_ROWS, into MAX-ROWS, etc.

Be sure you're clear about the difference between a prototype for a struct, and creating an instance of the struct.

How would u call a variable??
Rows[1].id = 6;

???

nvm i kinda got it...

Code:

struct Connection *p, test;
struct Database db;
p = &test;    
p->db = &db;    
p->db->rows[10].id = 10;     
printf("%d\n",p->db->rows[10].id);

Make sure to understand how to 'travel' through different structs. It is used very frequently