_Follow along with this video:_ --- ### Back to `enterRaffle` ```js function enterRaffle(address[] memory newPlayers) public payable { require(msg.value == entranceFee * newPlayers.length, "PuppyRaffle: Must send enough to enter raffle"); for (uint256 i = 0; i < newPlayers.length; i++) { players.push(newPlayers[i]); } // Check for duplicates for (uint256 i = 0; i < players.length - 1; i++) { for (uint256 j = i + 1; j < players.length; j++) { require(players[i] != players[j], "PuppyRaffle: Duplicate player"); } } emit RaffleEnter(newPlayers); } ``` Back to our `main entry point` function, we see it's using a require statement. Now, this contract is using `pragma 0.7.6`, so custom reverts may not have existed then - but this is a great example of a note we'd want to take and something we should check later. ```js function enterRaffle(address[] memory newPlayers) public payable { require(msg.value == entranceFee * newPlayers.length, "PuppyRaffle: Must send enough to enter raffle"); //@audit - Are custom reverts an option in 0.7.6? ... } ``` A few additional details we notice as we traverse the function: - Our require statement compares to `newPlayers.length` - _what happens if this is 0?_ - The `entranceFee` is an `immutable variable` - we can confirm this is initialized in the constructor. - The raffle is keeping track of who has entered the raffle by pushing each index of `newPlayers[]` to `players[]`. The last section of this function is finally our check for duplicates. ```js // Check for duplicates for (uint256 i = 0; i < players.length - 1; i++) { for (uint256 j = i + 1; j < players.length; j++) { require(players[i] != players[j], "PuppyRaffle: Duplicate player"); } } ``` With experience you'll be able to _smell_ bugs. You'll see messy blocks of code like the above and your intuition is going to kick in. Can you spot the bug🐛? ### Wrap Up We've learnt SO MUCH from this single entry point of this contract. I hope you've been taking notes of what we uncover as we go. These protocol's we're going through may be small in scope - but they won't always be. Building strong organizational habits now will benefit you later on. Next, let's take a look at a repo in which we've compiled simplified examples of common exploits, maybe we'll find the bug mentioned above!