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3aab9f lisa 2026-08-11 23:24:06
Add C06 skill-code study pages, linked from the SD hub Eleven pages ported from the applied-computing-au C06-Reference-Godot standard: home page with the 34-code lookup, per-topic pages with labelled GDScript examples, evidence standards, and Check Your Understanding fold blocks. Generated mirror — repo copy is canonical. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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<!-- Generated from applied-computing-au vic/unit3-4/sat/C06-2026/C06-Reference-Godot — do not hand-edit; re-run the port. -->
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# Control Structures — GDScript
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**Skill codes on this page**
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| Code | Level | Skill |
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|---|---|---|
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| C625 | 3–4 | control structure — sequence |
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| C626 | 3–4 | control structure — selection |
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| C632 | 5–6 | control structure — iteration / repetition |
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## C625 — Sequence
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**Definition.** A set of instructions that executes line by line in the order that it is written.
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Minimum two lines whose order matters — label the start and end:
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```gdscript
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# C625 sequence: start
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var zone: int = int($ZoneInput.text)
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var fare: float = FARE_TABLE[zone]
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balance -= fare
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$BalanceLabel.text = "Balance: $%.2f" % balance
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# C625 sequence: end
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```
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**Earns the tick:** a labelled block that breaks if you swap two lines. **Doesn't:** one isolated statement (that's C611).
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**In connect-go-dots** (`grid.gd`) — store the choice first, then switch screens:
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```gdscript
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# connect-go-dots — grid.gd
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func _open(photo: Texture2D) -> void:
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Shared.photo = photo # C625 sequence: store the choice…
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get_tree().change_scene_to_file("res://detail.tscn") # …then change scene
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```
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## C626 — Selection
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**Definition.** A control structure that allows a programmer to write lines of code that are only run when a particular requirement is met.
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### If
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When condition is met, flow is directed to the alternative instruction.
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```gdscript
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if condition: # C626 — selection
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# code
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```
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### If … Then … Else (chained selection)
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When condition is met, flow can be directed multiple times. *Chained selection:* more than one condition checked in sequence — each branch can test a different condition, and execution stops at the first branch whose condition is true.
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```gdscript
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if condition: # C626 — chained selection
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# code
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elif other_condition:
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# code
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else:
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# code
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```
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### Switch or Case (`match`)
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Choose between listed alternatives. Unlike chained selection, every case tests the *same* expression for equality against a different value.
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```gdscript
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match value: # C626 — selection: match
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1:
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# code
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2:
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# code
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```
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**In club-ladder** (`team.gd`) — a real `match`, with the wildcard `_` as the catch-all:
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```gdscript
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# club-ladder — team.gd
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func record(result: String) -> void:
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match result: # C626 — selection: match with a catch-all
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"win":
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wins += 1
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"draw":
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draws += 1
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_:
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losses += 1 # anything that is not a win or a draw
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```
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### Myki example
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```gdscript
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# C626 selection: pick the fare rule
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if is_concession:
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fare = FARE_TABLE[zone] * 0.5
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elif is_weekend:
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fare = WEEKEND_CAP
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else:
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fare = FARE_TABLE[zone]
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```
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*Nested selection* — a selection inside another selection's structure — is also C626 evidence; use the word "nested" in validation.
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**Earns the tick:** a condition that changes what runs, demonstrated with both outcomes. An `if` whose `else` can never happen is weak evidence.
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**In tile-matching-game** (`game.gd`) — both selection shapes:
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```gdscript
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# tile-matching-game — game.gd
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if is_busy or card.is_face_up or card.is_matched: # C626 — guard clause
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return # bail out early on any bad click
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if first_card.pair_id == second_card.pair_id: # C626 — selection: two outcomes
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_handle_match()
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else:
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await _handle_mismatch()
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```
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## C632 — Iteration / repetition
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**Definitions.** *WHILE:* an iteration repeated for as long as a condition is met. *FOR:* an iteration repeated a predefined number of times. *Infinite loop:* an iteration that will never reach the condition upon which it can terminate.
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### While …
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May not execute to satisfy condition.
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```gdscript
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while condition: # C632 — iteration
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# code
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```
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### Do … While
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May not execute if condition is not satisfied once.
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No `do … while` construct in GDScript — a pre-test `while` loop covers this behaviour:
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```gdscript
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while condition: # C632 — iteration
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# code
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```
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### Repeat … Until
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Executes at least once. If conditions are not met, there is a possibility of an **infinite loop**.
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No `repeat … until` construct in GDScript — emulate a post-test loop with `while true:` and a `break` when the condition is met:
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```gdscript
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while true: # C632 — post-test iteration
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# code
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if condition:
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break
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```
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### For … Next
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A counting loop to be executed a set number of times.
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```gdscript
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for i in range(10): # C632 — counting iteration
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# code
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```
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### For … In
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A counting loop that iterates over items in an array or list.
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```gdscript
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var cats = ["Whiskers", "Fluffy"]
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for cat in cats: # C632 — iteration over an array
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print(cat)
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```
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### Myki example
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```gdscript
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# C632 iteration: total up today's journeys
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var total: float = 0.0
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for journey in journeys:
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total += journey["fare"]
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```
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**In connect-go-dots** (`grid.gd`) — one loop wires every photo button:
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```gdscript
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# connect-go-dots — grid.gd
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for button in %Photos.get_children(): # C632 — iteration
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button.pressed.connect(_open.bind(button.texture_normal))
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```
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`get_children()` returns an array of the six `TextureButton`s and the loop visits each in turn. (`%Photos` finds the node by its scene-unique name.)
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**In tile-matching-game** (`deck.gd`) — a real `while` whose end is guaranteed:
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```gdscript
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# tile-matching-game — deck.gd
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while not file.eof_reached(): # C632 — ends when the file runs out of rows
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var row := file.get_csv_line()
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```
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**Earns the tick:** a loop over real data — a `for` over your own array, or a `while` whose condition provably terminates. Be ready to explain *why the loop ends*: the infinite-loop question is a validation favourite.
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## Check Your Understanding
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1. In a `match`, what does every case compare?
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>| ### Answer
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>| The *same* expression against a different value — unlike chained `elif`, where each branch can test something different.
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2. GDScript has no `repeat … until`. What is the accepted emulation?
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>| ### Answer
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>| `while true:` with `if condition: break` at the end of the body — runs at least once, tests after.
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3. What two questions about any loop should you be ready to answer live?
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>| ### Answer
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>| What it iterates over, and why it must end.