简单代币合约 / 学习智能合约#4

pragma solidity >=0.4.22 <0.7.0;

contract SimpleToken{
    mapping(address => uint256) public balanceOf;
    uint id;
    constructor() public{
        balanceOf[msg.sender] = 1000000;
    }

    function transfer(address _to, uint256 _value) public{
        require(balanceOf[msg.sender] >= _value);
        require(balanceOf[_to] + _value >= balanceOf[_to]);
        balanceOf[msg.sender] -= _value;
        balanceOf[_to] += _value;
    }
}

把帐本信息存入一个mapping(映射)中，实现简单的转帐功能！代币想发多少有多少！