# Numeric Literals

Numbers can be written in various bases. Numbers are assumed to be decimal by default. Non-decimal literals have a specific prefix.

| Numeral system  | Prefix | Characters                                                            |
| --------------- | ------ | --------------------------------------------------------------------- |
| **Decimal**     | *None* | one or more numbers (`0` to `9`)                                      |
| **Binary**      | `0b`   | one or more zeros or ones (`0` or `1`)                                |
| **Octal**       | `0o`   | one or more numbers in the range `0` to `7`                           |
| **Hexadecimal** | `0x`   | one or more numbers, or characters `a` to `f`, lowercase or uppercase |

```
// A decimal number
//
1234567890  // is `1234567890`

// A binary number
//
0b101010  // is `42`

// An octal number
//
0o12345670  // is `2739128`

// A hexadecimal number
//
0x1234567890ABCabc  // is `1311768467294898876`

// Invalid: unsupported prefix 0z
//
0z0

// A decimal number with leading zeros. Not an octal number!
00123 // is `123`

// A binary number with several trailing zeros.
0b001000  // is `8`
```

Decimal numbers may contain underscores (`_`) to logically separate components.

```
let largeNumber = 1_000_000

// Invalid: Value is not a number literal, but a variable.
let notNumber = _123
```

Underscores are allowed for all numeral systems.

```
let binaryNumber = 0b10_11_01
```