Why can't I add a String and an int?

Godot 4.x

The error

You’ll see something like one of these in the Debugger panel. The function and property names will be your own:

_on_coin_collected(): Invalid operands 'String' and 'int' in operator '+'.

_on_coin_collected(): Invalid assignment of property or key 'text' with value of type 'int' on a base object of type 'Label'.

Which cause is it?

What’s happening	Go to
The error mentions `operator '+'`	Gluing text and a number with plus
The error mentions `Invalid assignment of property or key 'text'`	Assigning a number straight to a text property
It works, but you want padding, decimals or a nicer layout	Formatting the number

The example scene

The script is on HUD and updates ScoreLabel every time a coin is collected.

HUDCanvasLayerscript attached here
- ScoreLabelLabelshows the score

Gluing text and a number with plus

+ on a String means “join two Strings”. score is an int, not a String, so Godot has nothing to join and stops:

GDScript
C#

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extends CanvasLayer
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@onready var score_label: Label = $ScoreLabel
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var score := 0
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func _on_coin_collected() -> void:
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  score += 1
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  score_label.text = "Score: " + score
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  score_label.text = "Score: " + str(score)

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using Godot;
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public partial class Hud : CanvasLayer
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{
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    private Label _scoreLabel;
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    private int _score;
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    public override void _Ready()
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    {
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        _scoreLabel = GetNode<Label>("ScoreLabel");
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    }
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    private void OnCoinCollected()
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    {
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        _score += 1;
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        _scoreLabel.Text = $"Score: {_score}";
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    }
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}

Fix: str() turns anything into a String. The C# version works as written because string interpolation ($"...") converts the number for you.

Assigning a number straight to a text property

text on a Label only accepts a String. Handing it an int fails the same way, just with a longer error:

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func _on_coin_collected() -> void:
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  score += 1
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  score_label.text = score
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  score_label.text = str(score)

The same goes for Button.text, LineEdit.text and RichTextLabel.text. Anything that isn’t already a String needs str() first.

Formatting the number

When you want more than a plain number, use the % operator or format() instead of str(). %d is a whole number, %.1f is a float with one decimal, and %03d pads with zeros to three digits:

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score_label.text = "Score: %d" % score
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score_label.text = "Score: %03d" % score
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time_label.text = "%.1f s" % time_left
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score_label.text = "Score: {0}".format([score])

Still stuck?

Hover the variable in the script editor to see its type, or drop print(typeof(score)) on the line above the failing one and run again. 4 means String, 2 means int, 3 means float. Whatever isn’t a String needs str() before it meets one. If the variable has no type, give it one (var score := 0 or var score: int = 0) so the editor can warn you before you run.

GDScript format stringsOfficial docs on the % operator and format().