Spotting sequence, branching and iteration in everyday systems

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Quick Questions

Shade in the A or B circle for each question.

1. A traffic light goes red, then green, then yellow, then back to red, always in that order. Which building block is this?

A Sequence (steps in order)

B Branching (a decision)

2. A self-serve checkout says: IF the item is not on the scale, THEN ask the shopper to try again. Which building block is this?

A Branching (a decision)

B Iteration (a repeat)

3. An automatic door keeps checking for people, again and again, all day. Which building block does the checking again and again show?

A Iteration (a repeat)

B Sequence (steps in order)

4. An alarm app rings every 5 minutes until you press stop. Which part of the algorithm is the repeat?

A Press the stop button once

B Ring again every 5 minutes until stop is pressed

5. An automatic door: IF a person is standing in front of the sensor, THEN open the door. What is the condition?

A The door opens

B A person is standing in front of the sensor

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1IF someone is at the door THEN open the door		A1. Show green 2. Show yellow 3. Show red
2REPEAT UNTIL alarm is turned off: ring again		BThe branch does the wrong action. When the light is red the cars should stop, not go.
3Sequence: a traffic light changes in the same order every time		CBranching: the automatic door makes a decision and only opens when its condition is true
4Branching: a self-serve checkout takes a different action depending on what happens		DIF item is scanned THEN beep ELSE show 'Try again'
51. Pay for items 2. Scan items 3. Pack bags		EThe steps are in the wrong order. A checkout sequence must scan the items before the customer pays.
6Traffic light: IF the light is red THEN go		FIteration: the alarm app repeats the same step over and over until a condition is met

Definitions

sequence, branching, iteration

Fill in the Blanks

Complete each line of code by filling in the missing parts.

IF pedestrian button is pressed ____ turn the traffic light red

IF person is near THEN open door ____ keep door shut

1. Scan item _. Put item in bag 3. Pay for items

REPEAT _______ change light to green change light to red

REPEAT _____ snooze is pressed ring alarm

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A Light turns green

B Light turns orange

C Light turns orange

D Wait 5 seconds

E Light turns red

Question 2

A Scan the item

B IF weight does not match THEN

C Print the receipt

D ELSE

E Add item to the bag

Question 3

A REPEAT FOREVER

B IF person is near THEN

C Open the door

D END IF

E Close the door

Question 4

A Set alarm for 7:00

B REPEAT 2 TIMES

C Play the alarm sound

D Wait 5 seconds

Question 5

A Check the crossing button

B IF button was pressed

C Light turns red for cars

D END IF

Answer Key

Spotting sequence, branching and iteration in everyday systems

Section A: Quick Questions

A — Sequence (steps in order)

A — Branching (a decision)

A — Iteration (a repeat)

B — Ring again every 5 minutes until stop is pressed

B — A person is standing in front of the sensor

Section B: Match the Pairs

IF someone is at the door THEN open the door → Branching: the automatic door makes a decision and only opens when its condition is true

REPEAT UNTIL alarm is turned off: ring again → Iteration: the alarm app repeats the same step over and over until a condition is met

Sequence: a traffic light changes in the same order every time → 1. Show green 2. Show yellow 3. Show red

Branching: a self-serve checkout takes a different action depending on what happens → IF item is scanned THEN beep ELSE show 'Try again'

1. Pay for items 2. Scan items 3. Pack bags → The steps are in the wrong order. A checkout sequence must scan the items before the customer pays.

Traffic light: IF the light is red THEN go → The branch does the wrong action. When the light is red the cars should stop, not go.

Section C: Definitions

sequence, branching, iteration — The three building blocks of algorithms: steps in order, decisions (IF) and repeats (loops). Traffic lights, self-serve checkouts, automatic doors and alarm apps all use them.

Section D: Fill in the Blanks

IF pedestrian button is pressed THEN
  turn the traffic light red

IF person is near THEN open door
ELSE keep door shut

1. Scan item
2. Put item in bag
3. Pay for items

REPEAT FOREVER
  change light to green
  change light to red

REPEAT UNTIL snooze is pressed
  ring alarm

Section E: Spot the Error

B — A sequence must keep its steps in order. The light should wait 30 seconds on green before it turns orange. Line 2 should be 'Wait 30 seconds'.

C — This is the branch for when the weight does not match, so the checkout should call a staff member. Printing a receipt here is the wrong action. Line 3 should be ' Call a staff member'.

D — Ending the IF early removes the ELSE branch. The door would then close every time, even when a person is near. Line 4 should be ' ELSE'.

B — An alarm app should keep repeating until the user taps Stop. A fixed 2 repeats would end even if you are still asleep. Line 2 should be 'REPEAT UNTIL I tap Stop'.

B — An IF decision needs the word THEN after its condition. Line 2 should be 'IF button was pressed THEN'.