# C Structures

> Learn how C structures group values of different types under one name using the struct keyword, access fields with a dot, and pass structs around by copy.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2020-02-28 | Topics: [C](https://flaviocopes.com/tags/clang/) | Canonical: https://flaviocopes.com/c-structures/

Using the `struct` keyword we can create complex data structures using basic C types.

A structure is a collection of values of different types. [Arrays](https://flaviocopes.com/c-arrays/) in C are limited to a type, so structures can prove to be very interesting in a lot of use cases.

This is the syntax of a structure:

```c
struct <structname> {
  //...variables
};
```

Example:

```c
struct person {
  int age;
  char *name;
};
```

You can declare variables that have as type that structure by adding them after the closing curly bracket, before the semicolon, like this:

```c
struct person {
  int age;
  char *name;
} flavio;
```

Or multiple ones, like this:

```c
struct person {
  int age;
  char *name;
} flavio, people[20];
```

In this case I declare a single `person` variable named `flavio`, and an array of 20 `person` named `people`.

We can also declare variables later on, using this syntax:

```c
struct person {
  int age;
  char *name;
};

struct person flavio;
```

We can initialize a structure at declaration time:

```c
struct person {
  int age;
  char *name;
};

struct person flavio = { 37, "Flavio" };
```

and once we have a structure defined, we can access the values in it using a dot:

```c
struct person {
  int age;
  char *name;
};

struct person flavio = { 37, "Flavio" };
printf("%s, age %u", flavio.name, flavio.age);
```

We can also change the values using the dot syntax:

```c
struct person {
  int age;
  char *name;
};

struct person flavio = { 37, "Flavio" };

flavio.age = 38;
```

Structures are very useful because we can pass them around as function parameters, or return values, embedding various variables within them, and each variable has a label.

It's important to note that structures are **passed by copy**, unless of course you pass a [pointer](https://flaviocopes.com/c-pointers/) to a struct, in which case it's passed by reference.

Using [`typedef`](https://flaviocopes.com/c-typedef/) we can simplify the code when working with structures.

Let's make an example:

```c
typedef struct {
  int age;
  char *name;
} PERSON;
```

> The structure we create using `typedef` is usually, by convention, uppercase.

Now we can declare new `PERSON` variables like this:

```c
PERSON flavio;
```

and we can initialize them at declaration in this way:

```c
PERSON flavio = { 37, "Flavio" };
```