Grades 3–5ComputationPlanned
Repetition and decisions
Repeating steps with loops, making decisions with if–then rules, and algorithms for arithmetic such as column addition, in unplugged activities and simple block-based programs.
math.comp.loops-and-conditions
The lesson for this topic has not been written yet. The outline below is part of the curriculum map and has not been reviewed.
Builds on
Required prerequisites, all the way down: 1
You will learn to
- Use a loop to shorten a sequence of repeated instructions, such as drawing a square.
- Write if–then rules for sorting objects or playing a simple game.
- Explain the written algorithm for column addition as a loop over place values with a carry.
Definition
- A loop repeats a block of instructions a fixed number of times or until a condition holds.
- A condition is a statement that is true or false, used to decide which instructions to follow.
Theorem
- 'Repeat 4 times: move forward, turn right 90°' draws a square.
- Column addition works through the digits from right to left, carrying 1 whenever a column sum is 10 or more.
Common misconceptions
- Thinking a loop must run forever or exactly once.
- Writing a stopping condition that can never become true, so that the loop never stops.
Leads to
Optional discoveries
- Computability Can we always tell whether a program will stop? No algorithm can decide this for every program: the halting problem is undecidable.
Further reading
- Tim Bell, Ian H. Witten and Mike Fellows, Computer Science Unplugged