Computer science · Grades K–4

Algorithms & logic · Quick reference 1

Reference sheet for Kindergarten to Grade 4: 5 key ideas, including robot on a number path, put the steps in order and robot moves on a grid. Follow the steps one at a time, in order, and keep track of where the robot is after each step.

Make a worksheet

Rule and key idea

Robot on a number path

Follow the steps one at a time, in order, and keep track of where the robot is after each step.

→ = 1 forward · ← = 1 back

A robot is on square 3. → means move 1 forward. ← means move 1 back. Steps: ← ← ←. Which square does the robot stop on? → 0

Put the steps in order

An algorithm is a list of steps in the right order. Ask: what has to happen before this step can work?

algorithm = steps in the right order

To wash your hands, which step comes first: “turn on the tap” or “rub your hands with soap”? → turn on the tap

Robot moves on a grid

Trace the path one arrow at a time. Columns change with ← and →; rows change with ↑ and ↓.

↑ row + 1 · ↓ row − 1 · → next column · ← previous column

A robot is on square D2 of a grid. Columns A to E go from left to right; rows 1 to 5 go from bottom to top. Each arrow moves it one square: ← ↓. Which square does it end on? → C1

Repeat loops

A loop repeats the same instructions. Multiply what happens inside the loop by the number of repeats.

repeat n times [k steps] → n × k steps

A robot runs: repeat 3 times [move forward 2 steps]. How many steps does it move in total? → 6

Find the bug

Debugging means checking each step against the plan to find the one that is wrong.

bug = a step that does not match the plan

A robot must move 4 squares to the right to reach a star, so every step should be →. Its program is: ↓ → → →. Which step number is the bug? → 1

Check yourself

Four practice questions on this topic. Try each one before you open the answer.

A robot is on square C2 of a grid. Columns A to E go from left to right; rows 1 to 5 go from bottom to top. Each arrow moves it one square: → ← → →. Which square does it end on?
- E3
- E2
- D2
- E1
Show the answer
E2 Start at C2, follow → ← → →, end at E2.
A robot is on square D5 of a grid. Columns A to E go from left to right; rows 1 to 5 go from bottom to top. Each arrow moves it one square: ↓ →. Which square does it end on?
- E4
- E3
- E5
- D4
Show the answer
E4 Start at D5, follow ↓ →, end at E4.
A robot is on square C4 of a grid. Columns A to E go from left to right; rows 1 to 5 go from bottom to top. Each arrow moves it one square: → →. Which square does it end on?
- D4
- E5
- E4
- E3
Show the answer
E4 Start at C4, follow → →, end at E4.
A robot is on square E4 of a grid. Columns A to E go from left to right; rows 1 to 5 go from bottom to top. Each arrow moves it one square: ↑ ↓ ↑. Which square does it end on?
- E5
- D5
- E4
- D4
Show the answer
E5 Start at E4, follow ↑ ↓ ↑, end at E5.