> 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/learn-gpc/flow-control.md).

# Flow control

### `if`, `else if`, `else`

```cpp
if(mode == 0) {
    // first path
} else if(mode == 1) {
    // second path
} else {
    // fallback
}
```

***

### `switch`, `case`, `default`

```cpp
switch(mode) {
    case 0: {
        set_val(TRACE_1, 10);
        break;
    }
    case 1: {
        set_val(TRACE_1, 20);
        break;
    }
    default: {
        mode = 0;
        break;
    }
}
```

Case values must be compile-time constants and unique. Braces are required around case bodies. Omit `break` only when fallthrough is deliberate and documented.

{% hint style="info" %}
Deliberate fallthrough still produces `GPC6018`. GPC has no annotation to mark it as intentional, so the warning appears on every case that falls through — expect it, and document the intent in a comment.
{% endhint %}

### `for`

```cpp
for(i = 0; i < sizeof(BUTTONS); i++) {
    // bounded work
}
```

### `while`

```cpp
while(i < 8) {
    i++;
}
```

### `do ... while`

```cpp
do {
    i++;
} while(i < 8);
```

***

### `break` and `continue`

`break` exits the nearest loop or switch. `continue` skips to the next iteration of the nearest loop. Neither is valid outside its allowed context.

***

### `return`

`return;` immediately exits the current user-created function. `return expression;` also supplies the function's result:

{% code title="return-value.gpc" %}

```cpp
function absolute(value) {
    if(value < 0) {
        return -value;
    }
    return value;
}
```

{% endcode %}

A bare `return;` exits without a value. Do not mix bare and valued returns in the same function. If execution reaches the end of a user function without returning a value, its result is `0`; callers may also ignore a user function's result.

{% hint style="info" %}
All real-time loops must have a provable quick exit. A loop that waits for a future physical event will lock the current VM cycle; use persistent state evaluated across `main` cycles instead.
{% endhint %}


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