> For the complete documentation index, see [llms.txt](https://max-daunarovich.gitbook.io/flow-network/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://max-daunarovich.gitbook.io/flow-network/introduction/built-in-functions.md).

# Built-In Functions

```
  fun panic(_ message: String): Never
```

Terminates the program unconditionally and reports a message which explains why the unrecoverable error occurred.

```
    let optionalAccount: Account? = // ...
    let account = optionalAccount ?? panic("missing account")
```

\-

```
  fun assert(_ condition: Bool, message: String)
```

Terminates the program if the given condition is false, and reports a message which explains how the condition is false. Use this function for internal sanity checks.

The message argument is optional.

```
  fun unsafeRandom(): UInt64
```

Returns a pseudo-random number.

NOTE: The use of this function is unsafe if not used correctly.

Follow [best practices](https://github.com/ConsenSys/smart-contract-best-practices/blob/051ec2e42a66f4641d5216063430f177f018826e/docs/recommendations.md#remember-that-on-chain-data-is-public) to prevent security issues when using this function.