# 3. Integer

The integer data type is used to store whole numbers - i.e. those without a decimal point.

For example

1234 is an integer

1234.0 is **not** an integer

An integer can deal with both positive and negative whole numbers.

If you try and store a decimal number in an integer data type, it will cut off everything after the decimal point, which is likely to cause a problem with the program later down the line. This 'type error' can be quite difficult to spot.

```
int MyInteger
MyInteger ← 1.234
```

The number in MyInteger will actally be 1, with the decimal part discarded.

#### Number size matters

Many computer languages (such as 'C') break down integer into different types depending on the kind of numbers you wish to store in it - its size and sign matter a great deal.

**unsigned int** - can only store zero and positive numbers up to 64,000 (it is 2^{16}-1) to be exact. It cannot store negative whole numbers.

**signed int** - stores zero and both positive and negative numbers but with only half the range of an unsigned int as one half of the range is dedicated to negative numbers. For example approximately +/- 32000 rather than 0 to +64000

**short int **- it only uses a single word (16 bits) for storage so the number must not be larger than about unsigned 64,000, or +/-32,000 if it's signed.

**long int** - it uses two words (32 bits) for storage and can handle huge numbers (unsigned 2^{32}-1 to be exact) , but it is wasteful of memory for small numbers.

**Challenge** see if you can find out one extra fact on this topic that we haven't
already told you

Click on this link: integer data type