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:

from top to bottom
one at a time
in the order written

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

Sequencing is simple but limited.

Selection (Decision-Making)

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

Without selection, programs cannot respond intelligently to input.

Iteration (Repetition)

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

Iteration continues until a condition is no longer met.

Combining Control Structures

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.