Lesson 8 of 8 · 36 min · Grades 6–8
Mini project — pocket money tracker
Kabir gets ₹50 at the start of the week. He spends on a pencil and a snack, then checks what is left for the piggy bank. This chapter is not a new idea — it is the previous chapters standing together: variables, a list of spends, a loop that subtracts, and a decision about saving. That is how real programs look: small ideas composed.
Pocket-money pouch
Combine skills into a small tool.
You will be able to
- ✓ Combine variables, lists, loops and if
- ✓ Print a clear money report a parent could check
- ✓ Change one spend and re-run without rewriting the whole story
Plan on paper, then translate
Write three sentences: start with 50; for each spend, subtract; if anything remains, save it. Those sentences become three parts of the program. If you cannot say it in the kitchen, you cannot code it yet.
Keep spends in a list so next week you add one number, not a new variable spend4. The loop does not care how many shops Kabir visited.
Running total
left = start copies the opening amount. Each loop turn does left = left - rupees. This pattern — an accumulator — appears in cricket run rates, lab inventories and bank ledgers.
Print after each subtraction if you want a receipt. Print once at the end if you only need the piggy-bank decision. Both are valid; receipts are easier to debug.
What you just learned, in one map
print showed facts. Variables named them. Arithmetic combined them. if chose a sentence. for repeated a subtraction. lists held many spends. You now have enough Python to automate a stall bill, a game score, or a class inventory — slowly, with tests, one print at a time.
- ● Name every input (start, spends).
- ● Loop the collection, do not copy-paste lines.
- ● End with a human sentence (Save / Empty), not a bare number.
Words that matter
- Accumulator
- A variable that updates inside a loop, like left.
- Composition
- Building a program from smaller skills you already have.
Common mistakes
Avoid: Subtracting from start each time instead of from left.
Do this: Keep a running left so each spend stacks.
Avoid: Hard-coding the final 18 rupees.
Do this: Let the loop compute remaining so new spends still work.
Example program — Kabir's week
Change a spend and watch remaining update. Then add a third spend to the list.
Edit the example, press Run, then Build if you want a compile check.
build
Press Build to compile.
Your turn — Your tracker
Start with 100. Spend 25 then 10. Print a line containing Save and the remaining 65.
Edit the example, press Run, then Build if you want a compile check.
build
Press Build to compile.
Self-assessment
Check your understanding before you mark the lesson complete.
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