HW05: Pocket money

Problem statement

Implement a smart contract for giving pocket money to a child.

• The contract should store the addresses of two parents and one child.
• The contract should store funds sent by the parents in ether.
• Only the parents and the child can access the funds.
• The parents can withdraw any amount at any time.
• There is a limit of 0.1 ether for single withdraws by the child. Moreover, between two withdrawals by the child, at least 4 weeks have to pass (i.e. the child can withdraw money roughly once a month).

Example scenario

Alice and Bob create a contract with 10 ether initial balance, giving access to their daughter, Claire. On the first day of every month, Claire withdraws 0.1 ether as her pocket money. If she tries to withdraw again during the month, she fails. If Alice or Bob needs some money, they can freely withdraw any amount from the contract.

Contract interface

• constructor: function PocketMoney(address parent2, address child) payable

  • The creator of the contract (msg.sender) is the first parent.
  • parent2 is the second parent.
  • child is the child.

• withdraw: function withdraw(uint256 amount)

  • Sends amount wei to the sender of the transaction.
  • Succeeds in two cases:
    • The sender is one of the parents.
    • The sender is the child, amount is not over the associated withdraw limit, and at least 4 weeks have passed since the last withdraw by the child.

• fallback: function () payable

  • Receives ether from any address.

Contract skeleton

pragma solidity ^0.4.21;

contract PocketMoney {

    // <contract_variables>

    // </contract_variables>

    function PocketMoney(address parent2, address child) public payable {
        // TODO
    }

    function withdraw(uint256 amount) public {
        // TODO
    }

    function () public payable {
        // TODO
    }

}