An automated double-door airlock system controls an inner door and an outer door. For safety reasons, both doors must never be open at the same time.
The system is controlled by the following algorithm:
1 WHILE (systemActive = True) DO
2
3 RECEIVE innerRequest FROM SENSOR_INNER
4 IF (innerRequest = True) THEN
5 SET innerDoor TO "Open"
6 END IF
7
8 RECEIVE outerRequest FROM SENSOR_OUTER
9 IF (outerRequest = True) THEN
10 SET outerDoor TO "Open"
11 END IF
12
13 IF (innerRequest = False) THEN
14 SET innerDoor TO "Closed"
15 END IF
16
17 IF (outerRequest = False) THEN
18 SET outerDoor TO "Closed"
19 END IF
20
21 END WHILE
State one condition allowed by the algorithm that does not meet the safety requirements for the airlock system.
159 exam-style questions on Edexcel GCSE Computer Science Algorithms, covering Constructs for solving problems, Variables, constants and data structures, Arithmetic, relational and logical operators, Tracing algorithm output with trace tables, Types of error and correcting logic errors, Standard algorithms (sorts and searches), and Evaluating algorithm fitness and efficiency. Each one has a worked solution and a mark scheme showing where the marks go.