Lesson 2: Flowchart Detectives

Big idea: A flowchart is a picture of an algorithm. Instead of writing instructions as words, we draw boxes and arrows that show exactly how a process flows — including decisions and loops.

Symbol Reference Card

Cut and glue into your journal to keep it as a handy reference throughout the term.

Flowcharts

VENDING MACHINE FLOWCHART:

Scenario A1: You insert a coin and select item B3, which IS in stock.

• At "Is the item in stock?" you take the __________ branch.
• Final output: ___________________________________________

Scenario A2: You insert a coin and select item D1, which is OUT OF STOCK.

• At "Is the item in stock?" you take the __________ branch.
• Final output: ___________________________________________

Scenario A3: You insert a coin and select item A2, which IS in stock. List every step you take in order:

Step 1: ____________________________________________________
Step 2: ____________________________________________________
Step 3: ____________________________________________________
Step 4: ____________________________________________________
Step 5: ____________________________________________________
Final output: ______________________________________________

NUMBER GUESSING FLOWCHART:

Scenario B1: Secret number is 7. Player guesses: 4, then 9, then 7.

Guess 1 (4): Is it correct? _____ Message shown: ___________________
Guess 2 (9): Is it correct? _____ Is it too high? _____ Message shown: ___________________
Guess 3 (7): Is it correct? _____ Message shown: ___________________

Scenario B2: Secret number is 2. Player guesses: 5, then 2.

Guess 1 (5): Message shown: ___________________ Guess 2 (2): Message shown: ___________________

Scenario B3: Secret number is 10. Player guesses 10 immediately. Steps taken:

Step 1: _____________________________________________________
Final output: ______________________________________________

Thinking question: Could this flowchart ever run forever? When would the game end?

Now swap sheets with a partner who did the OTHER flowchart.

Execute their flowchart using the same test scenarios. Do you get the same answers?

YES / NO — different at: ______________________

Activity 2 — Create Your Own Flowchart

Choose ONE of the four scenarios below. Draw your flowchart in your journal. Use the correct symbols from the reference card.

Scenario 1 — Lunchtime Decision You need to decide what to do at lunchtime. First: is it raining? If yes, go to the cafeteria. If no: is there a sports game on? If yes, go watch the game. If no, go to the courtyard.

Scenario 2 — Library Late Fee A student returns a library book. You need to calculate the fine. 0 days overdue \= no fine. 1–14 days \= small fine (50p). 15–30 days \= medium fine (£2.00). More than 30 days \= contact parents.

Scenario 3 — Getting Ready for School (harder — has loops!) Alarm goes off. Is it a school day? (If NO: go back to sleep, loop back.) If YES: have a shower. Is your uniform clean? (If NO: find an alternative.) Eat breakfast. Is your bag packed? (If NO: pack it.) Leave the house. END.

Scenario 4 — Troubleshooting a Computer (harder — has loops!) Computer won't turn on. Is it plugged in? (NO: plug it in → start again.) Is the power strip switched on? (NO: turn it on → start again.) Press power button. Does the power light come on? (NO: faulty power supply — contact IT → END.) Is the screen connected? (NO: connect screen.) Does the screen display anything? (NO: screen may be broken → END.) Computer is working → END.

I am doing Scenario: _____

Checklist before you start drawing:

• [ ] I know what my START is
• [ ] I know what all possible END points are
• [ ] I know how many decisions (diamonds) I need
• [ ] Every decision will have a YES path and a NO path

Partner Test

Swap your completed flowchart with a partner. Execute their flowchart using a test case you make up.

Flowchart I am testing: My partner's scenario _____

My test case (what inputs am I using?):

Steps I followed (write the sequence of boxes you moved through):

1. ___________________________________________
2. ___________________________________________
3. ___________________________________________
4. ___________________________________________
5. ___________________________________________
6. ___________________________________________

Final output / result: ___________________________________________________

Did the flowchart work correctly? YES / NO

If NO — what went wrong?

Reflection Questions

1. What are the four flowchart symbols? Fill in the table:

Symbol shape	Name	What it means
Oval
Rectangle
Diamond
Arrow

2. Why must every path through a flowchart eventually reach an END?

3. What is a loop in a flowchart? Give an example from one of the flowcharts in this lesson.

4. What made your partner's flowchart easy or hard to follow?

5. How is a flowchart similar to the navigation instructions you wrote in Lesson 1? How is it different?

Extension Challenges

A. Take your flowchart and rewrite it as a numbered list of instructions (like the Programmer's Notepad from Lesson 1). Which version is easier to understand — the flowchart or the list?

B. Flowchart B (the guessing game) loops forever if the player never guesses correctly. Add a "maximum number of guesses" feature — after 5 wrong guesses, the computer reveals the answer and the game ends. Draw the modified flowchart.

C. Can you make a flowchart for something that currently has no flowchart in your life — like your after-school routine, or how you decide what to watch on TV? Try it.