Index

Chapter 12: SafeMath Part 4

Great, now we can implement SafeMath on all the types of uints we used in our DApp!
Let's fix all those potential issues in ZombieAttack. (There was also one zombies[_zombieId].level++; that needed to be fixed in ZombieHelper, but we've taken care of that one for you so we don't take an extra chapter to do so 😉).

Putting it to the Test

Go ahead and implement SafeMath methods on all the ++ increments in ZombieAttack. We've left comments in the code to make them easy to find.

pragma solidity ^0.4.25;

import "./zombiehelper.sol";

contract ZombieAttack is ZombieHelper {
  uint randNonce = 0;
  uint attackVictoryProbability = 70;

  function randMod(uint _modulus) internal returns(uint) {
    // Here's one!
    // randNonce++;
    randNonce = randNonce.add(1);
    return uint(keccak256(abi.encodePacked(now, msg.sender, randNonce))) % _modulus;
  }

  function attack(uint _zombieId, uint _targetId) external onlyOwnerOf(_zombieId) {
    Zombie storage myZombie = zombies[_zombieId];
    Zombie storage enemyZombie = zombies[_targetId];
    uint rand = randMod(100);
    if (rand <= attackVictoryProbability) {
      // Here's 3 more!
      // myZombie.winCount++;
       myZombie.winCount =  myZombie.winCount.add(1);
      myZombie.level = myZombie.level.add(1);
      enemyZombie.lossCount = enemyZombie.lossCount.add(1);
      feedAndMultiply(_zombieId, enemyZombie.dna, "zombie");
    } else {
      // ...annnnd another 2!
      myZombie.lossCount = myZombie.lossCount.add(1);
      enemyZombie.winCount = enemyZombie.winCount.add(1);
      _triggerCooldown(myZombie);
    }
  }
}