Variables & Debugging

A variable is a labeled box inside a program. It holds a value — like a score, a name, or how many lives are left — and that value can change as the program runs. A constant is also a labeled box, but its value never changes. Knowing the difference helps you write clearer code and find bugs faster.

Variable vs Constant

• Variable — value can change. Examples: score, lives left, time on the clock.
• Constant — value stays fixed. Examples: pi, the gravity number, the screen width.
• Both have a clear name (a label) so you can read and update them in your code.

How a Variable Updates

When the player scores a point you tell the program: score = score + 1. The box called "score" now holds one more than before. Read the value with the variable name. Change the value by assigning a new one.

What is Debugging?

A bug is a mistake in the code. Debugging is the calm process of finding it and fixing it. Good programmers do not panic when something breaks — they slow down and check the code one line at a time.

1. Reproduce — run the program until you see the bug again.
2. Inspect — read the code and check the values of your variables.
3. Hypothesize — make a guess about which line is wrong and why.
4. Fix — change one thing, run again, and see if the bug is gone.

Common Bugs to Watch For

• Score never updates — you forgot to write score = score + 1.
• Loop runs forever — there is no stop condition.
• Wrong message shows — you used = (assign) instead of == (compare).
• Variable misspelled — "scor" is not the same box as "score".
• Off-by-one count — you started counting at 1 when you meant 0.
• Sprite never moves — an event is not connected to a motion block.