← IGCSE Computer Science Paper 1

Using digital currency to pay for goods and services

Spending digital currency online or in shops that accept it to buy goods and services. The payment is sent from your wallet app as an electronic transaction.

Part of: IGCSE Computer Science 0478 — 5.2 Digital Currency — Module 7

Understanding Using digital currency to pay for goods and services in IGCSE Computer Science Paper 1

What it does: The checkout step is where an online shopper picks digital currency as the way to pay for goods. The transaction holds the sender wallet, the receiving business wallet and the amount, so the payment is sent electronically. A business must choose to accept digital currency. Many shops still accept only cash or cards.

Common mistakes: Paying for something takes money out of your wallet, so the price must be subtracted: balance ← balance - price. You pay from a wallet app, so the app must be opened (OPEN_APP), not closed, before the payment can be sent.

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This module's key terms are also in a printable crossword (Modules 500–509) and word search (Modules 490–509).

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Learning
Duo
Which is a way to pay for goods with digital currency?
Post a bundle of coins to the online shopPay an online shop that accepts it, using your wallet app
Matches
pay(shop, coinsFromPocket)
↓
Digital currency is not physical coins. It is paid electronically from a wallet app, for example wallet.send(shop, amount).
Applying
Meanings
Term
Paying with digital currency
Meaning
Spending digital currency online or in shops that accept it to buy goods and services. The payment is sent from your wallet app as an electronic transaction.
Practice
price ← 12
Testing
Gaps
balance ← balance price
Check Answer
Spots
2balance ← 100
3balance ← balance + price

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Quick Questions

1. Which is a way to pay for goods with digital currency?
A. Post a bundle of coins to the online shop
B. Pay an online shop that accepts it, using your wallet app ✓
Digital currency is spent online or in shops that accept it. The payment is made from a wallet app, with no physical coins or notes.
2. Where can you spend digital currency?
A. Only at businesses that accept it ✓
B. At every shop in the world
A business must choose to accept digital currency. Many shops still accept only cash or cards.
3. What does a payment from your wallet app become?
A. An electronic transaction sent over the internet ✓
B. A paper receipt that is posted to the shop
The payment is sent as an electronic transaction. No physical item moves between the buyer and the seller.
4. Which of these can you buy with digital currency?
A. Goods and services, such as a game or a music subscription ✓
B. Nothing, because it can only be saved and never spent
Digital currency can pay for both goods (items) and services (things done for you) at businesses that accept it.
5. You are at the online checkout of a shop that accepts digital currency. What do you do?
A. Hand over digital coins to the delivery driver
B. Choose to pay with digital currency and approve the payment from your wallet ✓
At an online checkout you approve the payment from your wallet app. The transaction is then sent electronically.

Match the Pairs

wallet.send(shop, 0.002) → Sends a payment from your wallet app to a business as an electronic transaction.
shop.accepts(digitalCurrency) → Checks that the business takes digital currency, so you can pay it for goods or services.
Online shopping: at the checkout you choose to pay for your basket using digital currency. → checkout.payWith("digital currency")
Paying from a wallet app creates an electronic transaction that goes from your wallet to the business's wallet. → transaction = (myWallet, shopWallet, 0.01)
pay(shop, coinsFromPocket) → Digital currency is not physical coins. It is paid electronically from a wallet app, for example wallet.send(shop, amount).
pay(anyShop, digitalCurrency) → Digital currency can only be spent at businesses that accept it, so check shop.accepts(digitalCurrency) first.

Key Term

Paying with digital currency
Spending digital currency online or in shops that accept it to buy goods and services. The payment is sent from your wallet app as an electronic transaction.

Fill in the Blanks

1. price ← 15 balance ← balance - price
Hint: Type the operator that reduces the wallet balance after you pay.
2. IF balance >= price THEN SEND(wallet, shop, price)
Hint: Type the keyword that starts the actions to run when the wallet has enough money.
3. SEND(wallet, shop, price) OUTPUT "Payment sent"
Hint: Type the keyword that shows a message to the customer.
4. shop ← "Bookshop" SEND(wallet, shop, price)
Hint: Type the variable for the business that receives the payment.
5. IF balance >= price THEN SEND(wallet, shop, price) ELSE OUTPUT "Not enough funds"
Hint: Type the keyword that handles the case when the wallet cannot cover the price.

Spot the Error

Question 1
A price ← 15
B balance ← 100
C balance ← balance + price
D OUTPUT balance
Line C — Paying for something takes money out of your wallet, so the price must be subtracted: balance ← balance - price.
Question 2
A wallet ← CLOSE_APP()
B shop ← SELECT_SHOP()
C SEND_PAYMENT(wallet, shop)
Line A — You pay from a wallet app, so the app must be opened (OPEN_APP), not closed, before the payment can be sent.
Question 3
A item ← "Headphones"
B cost ← 45
C IF balance <= cost THEN
D PAY(cost)
E ENDIF
Line C — You can only pay if your balance is greater than or equal to the cost. The condition should be balance >= cost.
Question 4
A sender ← myWallet
B shop ← myWallet
C amount ← 20
D SEND(sender, shop, amount)
Line B — The payment must go to the business's wallet (shopWallet). Using myWallet would send the money back to yourself.
Question 5
A coin ← "Bitcoin"
B accepted ← shopAccepts(coin)
C IF accepted = FALSE THEN
D PAY(coin)
E ENDIF
Line C — You can only pay with digital currency where the business accepts it. The payment should happen when accepted = TRUE.

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