導言

本次範例模擬一個正式的Token合約，增加使用OpenZeppelin的SafeMath Module，提高運算安全性，並在contract設計上增加設定價格、買token、燒毀token、挖token、摧毀合約等幾個function。

程式碼

pragma solidity^0.4.25;
library SafeMath{
    function add(uint a, uint b) internal pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function sub(uint a, uint b) internal pure returns (uint c) {
        require(b <= a);
        c = a - b;
    }
    function mul(uint a, uint b) internal pure returns (uint c) {
        c = a * b;
        require(a == 0 || c / a == b);
    }
    function div(uint a, uint b) internal pure returns (uint c) {
        require(b > 0);
        c = a / b;
    }
}

contract ERC20_interface{
    address owner;
    mapping(address=>uint) balances;
    mapping(address=>mapping(address=>uint)) allowed;
    event Approval(
        address indexed owner,
        address indexed spender,
        uint value
    );
    event Tansfer(
        address indexed from, 
        address indexed to, 
        uint value
    );

    function balanceOf() public view returns(uint256);
    function allowance(address _owner,address _spender) public view returns(uint256);
    function transfer(address _to,uint _value) public returns(bool);
    function transferFrom(address _owner,address _spender,uint _value) public returns(bool);
    function approve(address _spender,uint _value) public returns(bool);
}
contract ERC20 is ERC20_interface{
    using SafeMath for uint;
    function balanceOf(address _owner) public view returns(uint256){
        return balances[_owner];
    }
    function allowance(address _owner,address _spender) public view returns(uint256){
        return allowed[_owner][_spender];
    }
    function transfer(address _to,uint _value) public returns(bool){
        require(balances[msg.sender] >= _value);
        balances[msg.sender].sub(_value);
        balances[_to].add(_value);
        emit Transfer(msg.sender,_spender,_value);
        return true;
    }
    function transferFrom(address _owner,address _spender,uint _value) public returns(bool){
        uint allowance = allowed[_owner][_spender];
        require(balances[_owner] >= _value,"owner haven't enough money to transfer");
        require(_value <= allowance,"_value can't more than allowance");
        balances[_owner].sub(_value);
        balances[_spender].add(_value);
        allowed[_owner][_spender].sub(_value);
        emit Transfer(_owner,_spender,_value);
        return true;
    }
    function approve(address _spender,uint _value) public returns(bool){
        
        allowed[msg.sender][_spender].add(_value);
        emit Approval(msg.sender,_spender,_value);
        return true;
    }
}


contract Token is ERC20{

    string public TokenName;//token名稱
    string public TokenSymbol; //token符號
    uint256 public decimal;
    uint256 public Price;   
    uint256 public TotalSupply;
    uint256 pbulic BurnAmount; 
    uint256 private weiToEther = 10**18;

    event Burn(address indexed _owner, uint256 _burnAmount);
    event Mint(address indexed _someone,uint256 _mintAmount);
    modifier onlyOwner{
        require(msg.sender == owner,"You are not Owner");
        _;
    }

    constructor(
        uint256 _initialSupply,
        string _tokenName,
        string _tokenSymbol,
        uint _decimal
    )
    public
    {
        TotalSupply = _inititalSupply;
        TokenName = _tokenName;
        TokenSymbol = _tokenSymbol;
        owner = msg.sender;
        balances[owner] = TotalSupply;
    }


    function setPrice(uint256 _setPrice) public onlyOwner{
        buyPrice = _setPrice;                
    }
    function buy() public payable {
        uint _amount = msg.value / BuyPrice* 10**uint(decimals)/weiToEther; 
        //買的價格除以賣的價格(價格*10**最小單位/ether最小單位)
        
        balances[msg.sender] = balances[msg.sender].add(_amount);
        
    }
    function burn(uint256 _burnAmount) public{
        require(balances[msg.sender] > 0 && _burnAmount > 0);
        TotalSupply = TotalSupply.sub(_burnAmount);//剩餘多少token總量
        BurnAmount = BurnAmount.add(_burnAmount); //總共燒毀多少token
        balances[msg.sender] = balances[msg.sender].sub(_burnAmount);
        emit Transfer(msg.sender,0x0,_burnAmount);
        emit Burn(msg.sender,BurnAmount);

    }
    function mint(address _to, uint256 _amount) public{
        TotalSupply = TotalSupply.add(_amount);
        balances[_to] = balances[_to].add(_amount);
        emit Mint(_to,_amount);
    }
    function withdraw(uint256 _amount) public onlyOwner{
        owner.transfer(_amount);
    }
    function kill() public onlyOwner{
        selfdestruct(owner);
    }
}

解說

(待補)