# Variables and Types

### Data types

C has several types of variables, but there are a few basic types:

- Integers - whole numbers which can be either positive or negative. Defined using
`char`

,`int`

,`short`

,`long`

or`long long`

. - Unsigned integers - whole numbers which can only be positive. Defined using
`unsigned char`

,`unsigned int`

,`unsigned short`

,`unsigned long`

or`unsigned long long`

. - Floating point numbers - real numbers (numbers with fractions). Defined using
`float`

and`double`

. - Structures - will be explained later, in the Structures section.

The different types of variables define their bounds. A `char`

can range only from -128 to 127, whereas a `long`

can range from -2,147,483,648 to 2,147,483,647 (`long`

and other numeric data types may have another range on different computers, for example - from –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 on 64-bit computer).

Note that C does *not* have a boolean type. Usually, it is defined using the following notation:

```
#define BOOL char
#define FALSE 0
#define TRUE 1
```

C uses arrays of characters to define strings, and will be explained in the Strings section.

### Defining variables

For numbers, we will usually use the type `int`

, which an integer in the size of a "word" the default number size of the machine which your program is
compiled on. On most computers today, it is a 32-bit number, which means the number can range from -2,147,483,648 to 2,147,483,647.

To define the variables `foo`

and `bar`

, we need to use the following syntax:

```
int foo;
int bar = 1;
```

The variable `foo`

can be used, but since we did not initialize it, we don't know what's in it. The variable `bar`

contains the number 1.

Now, we can do some math. Assuming `a`

, `b`

, `c`

, `d`

, and `e`

are variables, we can simply use plus, minus and multiplication operators
in the following notation, and assign a new value to `a`

:

```
int a = 0, b = 1, c = 2, d = 3, e = 4;
a = b - c + d * e;
printf("%d", a); /* will print 1-2+3*4 = 11 */
```

## Exercise

In the next exercise, you will need to create a program which prints out the sum of the numbers `a`

, `b`

, and `c`

.