WACE Computer Science ATAR Unit 3: programming and networks exam question types

What this guide covers

Unit 3 of the WACE Computer Science ATAR course covers programming (data types, control structures, functions, data structures, searching, sorting, testing and OOP) and network communications (models, protocols, addressing and troubleshooting). In the exam these topics appear as short-answer questions and as parts of longer scenario questions that use a source booklet. The practice quiz on this page drills the core facts; this guide shows the question types built on them.

SCSA's 2026 examination front cover lists 10 minutes reading and 3 hours working time: Section One is 20 short-answer questions (83 marks, 40%) and Section Two is 4 extended-answer questions (111 marks, 60%).

Question types you should expect

1. Trace an algorithm

You are given pseudocode or code and asked for its output, the value of a variable, or the error it contains. Use a trace table with one column per variable and one row per step. Loop bounds are where most errors hide: check whether the loop runs to 4 or stops at 3.

Revise control structures, data types and functions.

2. Choose and justify an algorithm or data structure

Match the need to the tool and give the reason: a dictionary for lookup by key, an array for ordered data accessed by position, binary search only on sorted data, and Big O to compare how running time grows. Know the headline complexities: linear search O(n), binary search O(log n), bubble, selection and insertion sort O(n²).

Revise arrays, dictionaries, searching, sorting and Big O.

3. Test, debug and design with objects

Produce test data (normal, boundary, invalid) for a stated rule, classify an error (syntax, runtime, logic), and identify OOP concepts in a class diagram or code: classes and objects, encapsulation, inheritance and polymorphism. Legal and ethical obligations of developers (licensing, privacy, accessibility) can also appear.

Revise software development, testing and OOP.

4. Calculate with addresses and subnets

Subnetting questions ask for the number of usable hosts, the network and broadcast address, or which subnet an address belongs to. Usable hosts are $2^h - 2$ where $h$ is the number of host bits. Subnets start at multiples of the block size in the interesting octet.

Revise IP addressing, subnetting and network components.

5. Explain models, protocols and troubleshooting

Place a protocol at its layer (HTTP application, TCP and UDP transport, IP network, Ethernet data link), compare TCP with UDP for a stated use, describe encapsulation, and choose a tool for a symptom (ping for reachability, traceroute to locate delay, nslookup for DNS problems).

Revise OSI and TCP/IP models and protocols.

Worked example

Question (exam style, 4 marks). A school network uses 192.168.10.0/27. State the number of usable hosts per subnet and the broadcast address of the first subnet, showing working.

Answer. A /27 leaves $32 - 27 = 5$ host bits, so each subnet has $2^5 = 32$ addresses and $2^5 - 2 = 30$ usable hosts. The block size is 32, so the first subnet runs from 192.168.10.0 to 192.168.10.31, and its broadcast address is 192.168.10.31.

Keep going

Continue with the Unit 4 data management and cyber security practice, then work through the practice questions on each dot point page.