Bank Account

Level: Intermediate 30–60 min

Concepts: StateValidationEdge CasesBoundaries

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Create a bank account that tracks transactions and enforces business rules.

Requirements

1. Open Account — create an account with an initial balance of 0
2. Deposit — add funds to the account
   • Amount must be positive
   • Records the transaction with date and amount
3. Withdraw — remove funds from the account
   • Amount must be positive
   • Cannot withdraw more than current balance (no overdraft)
   • Records the transaction with date and amount
4. Get Balance — returns the current balance
5. Print Statement — returns a formatted statement showing all transactions

Statement format:

Date       | Amount  | Balance
2026-01-15 |  500.00 |  500.00
2026-01-20 | -100.00 |  400.00
2026-01-25 |  200.00 |  600.00

Transactions are printed in chronological order with running balance.

Test Cases

Action	Amount	Expected Balance	Notes
Deposit	500	500
Deposit	200	700
Withdraw	100	600
Withdraw	700	600	Rejected — insufficient funds
Deposit	-50	600	Rejected — negative amount
Withdraw	-50	600	Rejected — negative amount
Deposit	0	600	Rejected — zero amount

Bonus

• Add transfer between two accounts — atomic operation, both sides must succeed
• Add overdraft limit — allow withdrawals up to a configurable negative balance
• Add interest calculation — apply monthly interest based on average daily balance
• Add transaction categories — tag transactions and filter statements by category