Lesson 3 · Computational Thinking
The 'Human Computer' activity — computers can't guess.
Here is the single most important thing to understand before you write any code:
A computer does exactly what you tell it — not what you meant.
A human friend fills in the gaps. Say "get me a glass of water" and they work out which glass, which tap, how full. A computer works out none of that. Leave out a step and it doesn't guess, doesn't ask, doesn't use common sense. It either does something absurd, or stops completely.
That sounds like a weakness. It's actually the reason computers are useful: they do the same thing, exactly, every single time.
A student wrote instructions for making Maggi. Here's what they wrote, and what a literal computer would actually do:
| The instruction | What a computer does |
|---|---|
| "Boil water" | Boils water. Which water? How much? It takes any water, any amount. |
| "Add the noodles" | Adds the noodles — still inside the packet. Nobody said to open it. |
| "Add masala" | The whole sachet, plastic and all. |
| "Cook for 2 minutes" | Waits two minutes. But the stove was never switched on. |
| "Serve" | Tips raw noodles into a bowl of cold water. |
Every single instruction was followed perfectly. The result is still inedible.
The only way to feel this properly is to be the computer. Find one partner and run this — it takes five minutes, and it's genuinely funny when it goes wrong.
Choose something you could do without thinking: draw a square, make a paper plane, tie a shoelace, brush your teeth.
Which of these instructions would a computer be unable to follow?
This chapter is free — open this lesson in your portal to save your answers and track progress.
Write instructions for brushing your teeth — then hunt for the gaps yourself.
Go through your list line by line and ask of every step: "Could someone follow this wrongly and still be obeying me?"
Rewrite every step where the answer is yes.
When a program misbehaves, the computer almost never 'went wrong'. It followed your instructions perfectly — and your instructions had a gap. Fix the instructions, not the computer. Remember this and debugging will make sense from day one.
Here is a genuinely terrible instruction:
"Draw a nice house."
Rewrite it as a numbered list precise enough that everyone in your class draws the same house, without seeing each other's work.
Then say which single word in the original caused the most trouble — and why.