Sequence, selection and iteration
Every program ever written is built from three structures. Recognise them and unfamiliar code stops being frightening.
Part of your national curriculum
- Algorithms and programming: Design, use and evaluate computational abstractions that model the state and behaviour of real-world problems and physical systems
- Algorithms and programming: Understand several key algorithms that reflect computational thinking, and use logical reasoning to compare the utility of alternative algorithms for the same problem
- Algorithms and programming: Understand simple algorithms, expressed using sequence, selection and iteration, and correct errors in algorithms
Lesson overview
What you'll learn in this lesson
Design algorithms using sequence, selection and iteration
Key learning points
- • The three structures
- • Planning first
This lesson at a glance
- 25 minutes
- 13 parts to scroll through
- 3 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 13
Visual introductionPicture this
Sequence, selection and iteration
Every program ever written is built from three structures. Recognise them and unfamiliar code stops being frightening.
In a nutshell
Design algorithms using sequence, selection and iteration
Explore the idea
Part 2 of 13
Learn
The three structures
Sequence runs steps in order. Selection chooses with if/else. Iteration repeats with for or while loops.
Explore the idea
Part 3 of 13
Learn
Planning first
Write the steps in plain English or pseudocode before typing. Decomposition — breaking one big problem into small ones — is the actual skill.
Reset break
Part 4 of 13
Pause
That's sitting 1 of 3 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 5 of 13
Quick check
Part 6 of 13
Quick check
Part 7 of 13
Reset break
Part 8 of 13
Pause
That's sitting 2 of 3 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 9 of 13
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 10 of 13
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
____ runs steps in order.
____ chooses with if/else.
____ repeats with for or while loops.
Challenge round
Part 11 of 13
Game · Recall cards
An if/else statement is…
Card 1 of 4
Mastery quiz
Part 12 of 13
Marked quiz
End of lesson quiz: Sequence, selection and iteration
4 questions, marked with the reasoning shown. No timer.
1. An if/else statement is…
2. A while loop is an example of…
3. Decomposition means…
4. An algorithm repeats 'move forward' until a wall is reached, then turns right. Which programming ideas does it use?
Lesson round-up
Part 13 of 13
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
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Points this lesson
0
Best run
0 in a row
Luna: 0 out of 3 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 13 · Watch & discover
How this is going
- Not looked at yet
Design, use and evaluate computational abstractions that model the state and behaviour of real-world problems and physical systems
- Not looked at yet
Understand several key algorithms that reflect computational thinking, and use logical reasoning to compare the utility of alternative algorithms for the same problem
- Not looked at yet
Understand simple algorithms, expressed using sequence, selection and iteration, and correct errors in algorithms