Lottery.sol

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity >=0.5.0 <0.9.0;

contract Lottery {
  // As of Solidity 0.5.0 the `address` type was split into `address` and
  // `address payable`, where only `address payable` provides the transfer
  // function. We therefore need to explicity use the `address payable[]`
  // array type for the players array.
  address public manager;
  address payable[] public players;

  // As of Solidity 0.5.0 constructors must be defined using the `constructor`
  // keyword. See https://docs.soliditylang.org/en/latest/050-breaking-changes.html#constructors
  //
  // As of Solidity 0.7.0 visibility (public / internal) is not needed for
  // constructors anymore. To prevent a contract from being created,
  // it can be marked abstract.
  constructor() {
    manager = msg.sender;
  }

  function enter() public payable {
    // Note: Although optional, it's a good practice to include error messages
    // in `require` calls.
    require(msg.value >= .01 ether, "A minimum payment of .01 ether must be sent to enter the lottery");

    // As of Solidity 0.8.0 the global variable `msg.sender` has the type
    // `address` instead of `address payable`. So we must convert msg.sender
    // into `address payable` before we can add it to the players array.
    players.push(payable(msg.sender));
  }

  function random() private view returns (uint256) {
    // For an explanation of why `abi.encodePacked` is used here, see
    // https://github.com/owanhunte/ethereum-solidity-course-updated-code/issues/1
    //
    // VM Paris Update: Note that in September 2022, Ethereum transitioned to proof-of-stake consensus,
    // also known as The Merge. One of the changes this resulted in was the introduction of a new
    // opcode called 'prevrandao', which replaces the 'difficulty' opcode. As such, since Solidity 0.8.18
    // block.difficulty has been deprecated and instead, block.prevrandao should be used.
    return uint256(keccak256(abi.encodePacked(block.prevrandao, block.number, players)));
  }

  function pickWinner() public onlyOwner {
    uint256 index = random() % players.length;

    // As of Solidity 0.4.24 at least, `this` is a deprecated way to get the address of the
    // contract. `address(this)` must be used instead.
    address contractAddress = address(this);

    players[index].transfer(contractAddress.balance);
    players = new address payable[](0);
  }

  function getPlayers() public view returns (address payable[] memory) {
    return players;
  }

  modifier onlyOwner() {
    require(msg.sender == manager, "Only owner can call this function.");
    _;
  }
}