Control Structures¶

Control structures determine how a program flows.

They decide: - which instructions run - when they run - how often they run

Every non-trivial program uses control structures.

Sequencing¶

Sequencing is the default behaviour of a program.

Instructions run: 1. from top to bottom 2. one at a time 3. in the order written

If no decisions or loops are used, a program relies entirely on sequencing.

Sequencing is simple but limited.

Selection allows a program to choose between paths.

A condition is checked, and one of two (or more) actions occurs.

Common uses: - checking user input - responding to player actions - enforcing rules

Figure 4 — Selection using a decision condition

flowchart TD
    Condition{Condition True?}
    Condition -->|Yes| ActionA[Run Action A]
    Condition -->|No| ActionB[Run Action B]

Without selection, programs cannot respond intelligently to input.

Iteration allows a program to repeat actions.

This is done using loops.

Common uses: - repeating game updates - counting down values - checking conditions repeatedly

Figure 5 — Iteration using a loop condition

flowchart TD
    Start --> Check{Condition Met?}
    Check -->|Yes| Loop[Repeat Action]
    Loop --> Check
    Check -->|No| End

Iteration continues until a condition is no longer met.

Most programs combine: - sequencing - selection - iteration

For example: - a loop repeats - a condition is checked inside the loop - different actions occur based on the result

This combination creates complex behaviour from simple rules.

Many bugs are caused by: - incorrect conditions - loops that never stop - logic that never runs

Understanding control structures makes bugs easier to identify and fix.

In AS92004, you must: - use control structures correctly - explain why they are needed - show how they affect program behaviour

Using a control structure without understanding it is risky.

Control structures are essential for: - player movement - collision handling - scoring systems - win/lose conditions

They are used constantly in game development.

End of Control Structures