创建自己的数字货币（代币）进行ico

ERC20 Token

ERC20和代币经常一同出现， ERC20是以太坊定义的一个代币标准。
要求我们在实现代币的时候必须要遵守的协议，如指定代币名称、总量、实现代币交易函数等，只有支持了协议才能被以太坊钱包支持。
其接口如下：

contract ERC20Interface {
string public constant name = "Token Name";
string public constant symbol = "SYM";
uint8 public constant decimals = 18;  // 18 is the most common number of decimal places
function totalSupply() public constant returns (uint);
function balanceOf(address tokenOwner) public constant returns (uint balance);
function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
function transfer(address to, uint tokens) public returns (bool success);
function approve(address spender, uint tokens) public returns (bool success);
function transferFrom(address from, address to, uint tokens) public returns (bool success);
event Transfer(address indexed from, address indexed to, uint tokens);
event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

简单说明一下：
name ： 代币名称
symbol： 代币符号
decimals： 代币小数点位数，代币的最小单位， 18表示我们可以拥有 .0000000000000000001单位个代币。
totalSupply() : 发行代币总量。
balanceOf(): 查看对应账号的代币余额。
transfer(): 实现代币交易，用于给用户发送代币（从我们的账户里）。
transferFrom(): 实现代币用户之间的交易。
allowance(): 控制代币的交易，如可交易账号及资产。
approve(): 允许用户可花费的代币数。

编写代币合约代码

代币合约代码：

pragma solidity ^0.4.16;
interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }
contract TokenERC20 {
string public name;
string public symbol;
uint8 public decimals = 18;  // 18 是建议的默认值
uint256 public totalSupply;
mapping (address => uint256) public balanceOf;  // 
mapping (address => mapping (address => uint256)) public allowance;

event Transfer(address indexed from, address indexed to, uint256 value);

event Burn(address indexed from, uint256 value);


function TokenERC20(uint256 initialSupply, string tokenName, string tokenSymbol) public {
    totalSupply = initialSupply * 10 ** uint256(decimals);
    balanceOf[msg.sender] = totalSupply;
    name = tokenName;
    symbol = tokenSymbol;
}


function _transfer(address _from, address _to, uint _value) internal {
    require(_to != 0x0);
    require(balanceOf[_from] >= _value);
    require(balanceOf[_to] + _value > balanceOf[_to]);
    uint previousBalances = balanceOf[_from] + balanceOf[_to];
    balanceOf[_from] -= _value;
    balanceOf[_to] += _value;
    Transfer(_from, _to, _value);
    assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
}

function transfer(address _to, uint256 _value) public {
    _transfer(msg.sender, _to, _value);
}

function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
    require(_value <= allowance[_from][msg.sender]);     // Check allowance
    allowance[_from][msg.sender] -= _value;
    _transfer(_from, _to, _value);
    return true;
}

function approve(address _spender, uint256 _value) public
    returns (bool success) {
    allowance[msg.sender][_spender] = _value;
    return true;
}

function approveAndCall(address _spender, uint256 _value, bytes _extraData) public returns (bool success) {
    tokenRecipient spender = tokenRecipient(_spender);
    if (approve(_spender, _value)) {
        spender.receiveApproval(msg.sender, _value, this, _extraData);
        return true;
    }
}

function burn(uint256 _value) public returns (bool success) {
    require(balanceOf[msg.sender] >= _value);
    balanceOf[msg.sender] -= _value;
    totalSupply -= _value;
    Burn(msg.sender, _value);
    return true;
}

function burnFrom(address _from, uint256 _value) public returns (bool success) {
    require(balanceOf[_from] >= _value);
    require(_value <= allowance[_from][msg.sender]);
    balanceOf[_from] -= _value;
    allowance[_from][msg.sender] -= _value;
    totalSupply -= _value;
    Burn(_from, _value);
    return true;
  }
}