solidity例子分析（五）

pragma solidity ^0.4.19;
import "./zombiehelper.sol";

contract ZombieAttack is ZombieHelper {
  uint randNonce = 0;
  //设定概率
  uint attackVictoryProbability = 70;
  //产生不安全，但在这个例子里完全够用的随机数
  function randMod(uint _modulus) internal returns (uint) {

    randNonce ++;
    return uint(keccak256(abi.encodePacked(now, msg.sender, randNonce))) % _modulus;
  }
  //根据设定的概率胜负判定，并修改相应状态
  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){
      myZombie.winCount = myZombie.winCount.add(1);
      myZombie.level = myZombie.level.add(1);
      enemyZombie.lossCount = enemyZombie.lossCount.add(1);

      feedAndMultiply(_zombieId, enemyZombie.dna, "zombie");
    }
    else{
      myZombie.lossCount = myZombie.lossCount.add(1);
      enemyZombie.winCount = enemyZombie.winCount.add(1);
      _triggerCooldown(myZombie);
    }
  }
}