> For the complete documentation index, see [llms.txt](https://guide.cronuszen.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://guide.cronuszen.com/gpcscripting/gpc-script-guide/start-here/the-smallest-useful-script.md).

# The smallest useful script

Every GPC script needs `main` logic. Zen runs it repeatedly from top to bottom, once per VM cycle.

{% code title="smallest-useful-script.gpc" lineNumbers="true" %}

```cpp
main {
    if(get_val(PS5_L2)) {
        set_val(PS5_R1, 100);
    }
}
```

{% endcode %}

***

### What each part does

| Function               | Purpose                                           |
| ---------------------- | ------------------------------------------------- |
| `get_val(PS5_L2)`      | Reads the current L2 value.                       |
| `set_val(PS5_R1, 100)` | Writes a fully pressed R1 to the outgoing report. |

***

### How it runs

{% stepper %}
{% step %}

#### Read

`get_val(PS5_L2)` reads the current L2 value.
{% endstep %}

{% step %}

#### Evaluate

Any nonzero value is true in an `if` condition.
{% endstep %}

{% step %}

#### Write

While L2 is active, `set_val(PS5_R1, 100)` makes the outgoing R1 value fully pressed.
{% endstep %}

{% step %}

#### Send

At the end of `main`, Zen finalizes and sends the output report.
{% endstep %}
{% endstepper %}

{% hint style="info" %}
This does not create a permanent state. The condition is evaluated again on the next VM cycle.
{% endhint %}

<details>

<summary>Can I use more than one <code>main</code> section?</summary>

Zen Studio Live accepts more than one `main` section and merges them into one combined section. Use a single `main` section in new scripts unless splitting generated source is genuinely useful.

</details>


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