[\<- Notes 01/13](01-13.md)

---

Notes 01/15/2020

# Review Pointers

Below is an example to demonstrate pointer precedence:

```
int x[] = {0, 5, 10, 15, 20, 25, ...};
int y = 5;
int *p = x;

y = ++*p
printf("%d, %d\n", y, *p);
y = *(++p);
printf(...); //ditto
y = ++(*p);
printf(...); //ditto
```

The code outputs the following:

```
1, 1
5, 5
6, 6
```
---

# Introduction to Structures in C

- Earlier we talked about data types: int, char
- A Structure allows for multiple data types in one array
- Structure Basics
	- A structure is a collection of values, called members

- Outline of Structure Definition:

```
struct name{
	variable declaration;
	variable declaration;
	...
};
```

- The keyword struct signifies that this is a structure definition

- Example:

```
struct info{
	int number;
	char character;
	char string[10];
	int array[10];
};
```

- As can be seen in the example, multiple different data types are included as members of `info`
- This example **does not allocate any memory**
	- Instead, it simply tells C that now there is a new kind of data type called `struct info`

- Let's create a sample `struct info`:

```
struct info real_info;
struct info *p;
```

- Memory **is** allocated for real\_info
- Member variables of a struct can be accessed using `.`
	- For example:

```
p = &real_info //*p will point to real_info now
real_info.number = 2;
real_info.character = 'A';
```

- Let's see a visual representation of real\_info in memory

| real_info.number | real_info.character | real_info.string[] | real_info.array[] |
| - | - | - | - |
| 2 | 'A' | ... | ... |

- `real_info.string[]` and `real_info.array[]` show `...` because to show the full visual representation in memory, I would have to show `real_info.string[0]`, `real_info.string[1]`, etc.

- To access structure members with a pointer (such as `*p` defined above), use `->`
	- For example:

```
p->number = 2;
p->character = 'B';
p->array[0] = 3;
```

- The above code changes three members of real\_info in memory to the following:

| real_info.number | real_info.character | real_info.string[] | real_info.array[0] |
| - | - | - | - |
| 2 | 'B' | ... | 3 |

---

- Another Example:

```
struct node{
	int number;
	struct node *link;
};
```

- We will talk more about links later