![](https://cdn.pixabay.com/photo/2013/07/12/15/02/fingers-149295_960_720.png) (Image Source: [Pixabay](https://cdn.pixabay.com/photo/2013/07/12/15/02/fingers-149295_960_720.png))

最近在学习写Solidity的合约，最好的学习办法就是边写边学，所以就试着写了一个剪刀石头布的合约

这个合约挺简单，就是你出石头(0),布(1),剪刀(2)并发送ETH到合约地址，如果你获胜会获得双倍奖励，如果平局就会把发送的ETH退回，输了就没收ETH

这是合约代码：

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pragma solidity ^0.5.0;
contract RockPaperScissors{
    //rock-0
    //paper-1
    //scissors-2
    
     uint computerChoice;

  event sentPrize(uint computerChoice,uint playerChoice);

    function play(uint num)public payable{
        computerChoice = random();
        if(num-computerChoice==uint(-1) || num-computerChoice==uint(2)){
            sendMoney(msg.value*2);
        }else if(num-computerChoice==0){
            sendMoney(msg.value);
        }else{
            //you lose
        }
        emit sentPrize(computerChoice,num);
    }
    //get random number between 0-2
    function random() private view returns(uint){
        return block.timestamp%3;
    }
    //Send prize
    function sendMoney(uint amount) private{
        address payable player = msg.sender;
        player.transfer(amount);
        
    }
    
    //Get contract balance
    function getBalance()public view returns(uint){
       return address(this).balance;
    }
    
}

这个只是很简单的合约，里面也有一些问题，比如：

  • 随机出拳是按timestamp算的，所以很容易猜到合约下一个出拳是什么
  • 合约初始没有初始金