> For the complete documentation index, see [llms.txt](https://docs.werwolv.net/pattern-language/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.werwolv.net/pattern-language/core-language/in-out-variables.md).

# In / Out Variables

In and Out variables are a way to pass config or input data into the pattern and read result data back out from the pattern.

Each `in` and `out` variable creates an entry in the Settings tab of the Pattern Editor view. `in` variables create an input field, `out` variables create a label.

Before executing the pattern, the user can now enter a value in the input field of the `in` variable. This value will be copied into the corresponding `in` variable before the pattern is executed.

Likewise, once the pattern has finished executing, whatever value has been written to the `out` variable will be displayed in the label.

The following code shows a simple pattern that reads in the value of `inputValue`, multiplies it by two and then writes it back into `outputValue`.

```rust
u32 inputValue in;
u32 outputValue out;

fn main() {
    outputValue = inputValue * 2;
};
```

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