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# Local and Global Variables — GDScript


**Skill codes on this page**

| Code | Level | Skill |
|---|---|---|
| C621 | 3–4 | local variables |
| C622 | 3–4 | constants |
| C628 | 3–4 | uses data types for local variables |
| C631 | 5–6 | global variables |
| C634 | 5–6 | uses appropriate data types for global variables |

**Definition.** A *variable* stores and labels data to be referenced and manipulated in a program. Its **scope** is the part of the program that can see it.

| | Where it is written | Who can see it |
|---|---|---|
| **Local (C621)** | Inside a function | Only that function |
| **Global (C631)** | Outside every function, at script level | Every function in the script |

**Quick check:** is the line indented inside a `func`? Local.

## C621 — Local variables

**Definition.** Variables defined inside a function that can only be accessed by that function.

```gdscript
func calculate_fare() -> void:
    # C621 — local variable: only calculate_fare() can see it
    var fare: float = 5.30
    balance -= fare
```

Parameters and loop variables are local too — in `connect-go-dots/grid.gd`, the parameter `photo: Texture2D` and the loop variable `button` exist only inside their function.

## C631 — Global variables

**Definition.** Variables defined outside any function that can be accessed by all functions throughout the source code.

At the script level:

```gdscript
extends Control

# C631 — global variables: every func in this script can use them
var balance: float = 20.00
var is_concession: bool = false
```

Or using `class_name` with `static` for access from other scripts:

```gdscript
class_name GlobalVars

static var g_var = 20   # C631 — global via class_name
```

An **autoload singleton** is the Godot-idiomatic project-wide global — if you use one, name it as your C631 evidence in validation.

**In connect-go-dots** — the autoload in action (`shared.gd`, registered as `Shared`):

```gdscript
# connect-go-dots — shared.gd (autoload "Shared")
extends Node

## Handed from one screen to the next. Lives on root, so a scene change
## cannot touch it.
var photo: Texture2D   # C631 — global: both screens use it
```

```gdscript
Shared.photo = photo            # C631: grid.gd — one screen writes it
%Photo.texture = Shared.photo   # C631: detail.gd — the other reads it
```

The `##` comment is model internal documentation: it says *why* the variable lives where it does.

## C622 — Constants

**Definition.** A fixed value that, once defined, cannot be altered during the execution of a program.

```gdscript
# C622 — constant: the daily cap never changes while the program runs
const DAILY_CAP: float = 9.60
```

**Earns the tick:** `const` used for a value that genuinely never changes, named in CAPITALS. Showing Godot's error when you try to assign to it is a neat validation demo.

## C628 and C634 — choosing the right data type

C621/C631 is that the variable **exists**. C628/C634 is that its data type **suits the data** — C628 for locals, C634 for globals.

```gdscript
extends Control

var trips_today: int = 0          # C634 — int: you cannot take half a trip
var balance: float = 20.00        # C634 — float: money needs decimal places
var is_concession: bool = false   # C634 — bool: only two possible answers
var card_id: String = ""          # C634 — String: digits never used in a calculation

func charge(zone: int) -> void:
    var fare: float = FARE_TABLE[zone]   # C628 — float: fares have cents
    balance -= fare
```

From tile-matching-game (`deck.gd`):

```gdscript
# tile-matching-game — deck.gd
var key: String = card["pair"]   # C628 — String: the pair label from the CSV
```

**State the data type.** `var trips_today = 0` cannot earn C634 because no data type has been given for the marker to assess. Always write `: int`, `: float`, `: bool` or `: String`.

`var trips_today := 0` is acceptable — GDScript works out the type for you — but name it in your comment so the marker can see it: `# C634 — int: you cannot take half a trip`.

Types go beyond `int`/`float`/`bool`/`String`: in connect-go-dots the global is `var photo: Texture2D` — same standard, `# C634 — Texture2D: the value is an image`.

The **why** in these comments doubles as your reasoning evidence (C629/C638) — see [Data Types](/sd/C06/Data%20Types).

## Check Your Understanding

1. `var speed := 5` at script level — which code does it earn as written, and what more would C634 need?

>| ### Answer
>| C631 (a global exists). C634 needs the type visible — write `: int`, or name it in the comment — plus the *why*.

2. Are function parameters local or global?

>| ### Answer
>| Local (C621): they exist only inside their function.

3. What three things make a C622 constant?

>| ### Answer
>| `const`, a CAPITALS name, and a value that genuinely never changes while the program runs.