1. Which construct chooses between two actions?
- Selection
- Storage
- Translation
Check the answer and reasoning
Selection
An IF condition selects a branch based on a Boolean result.
CS / Foundations
Algorithms, sequence and decisions
An algorithm is a finite, precise method for solving a defined problem. Sequence orders instructions, selection chooses branches and iteration repeats actions.
Learning objectives
- Explain algorithms, sequence and decisions using a concrete example.
- Apply the worked method and justify each step.
- Recognise the limitation described in the final check.
The big idea
An algorithm is a finite, precise method for solving a defined problem. Sequence orders instructions, selection chooses branches and iteration repeats actions.
Trace an algorithm by recording variable values after each operation. Testing examples can reveal bugs, while a convincing correctness argument explains why all permitted inputs are handled.
Worked example
Start x=2, then set x←x+3, then x←2x. What is x?
Follow the solution
After addition x is 5; doubling gives 10.
Investigate and explain
Predict the worked result before calculating. Change one input, record the new result, and explain which assumptions still hold.
Use the prediction activity below; a local model appears only where it supports this topic.
Check your understanding
2. Start x=2, then set x←x+3, then x←2x. What is x?
- 7
- 10
- 8
Check the answer and reasoning
10
After addition x is 5; doubling gives 10.
3. If a loop condition never becomes false, what may happen?
- Automatic correctness
- Guaranteed termination
- An infinite loop
Check the answer and reasoning
An infinite loop
A terminating loop needs progress toward a condition that ends repetition.