erc20interface.sol

pragma solidity ^0.4.20;

contract ERC20Interface{
    string public name;  //名字
    string public symbol;  //符号
    uint8 public decimals;  //小数点位数 
    uint public totalSupply;  //总量 
    
    function transfer(address _to, uint256 _value) returns (bool success);
    function transferFrom(address _spender, uint256 _value) returns (bool success);
    
    function approve(address _spender, uint256 _value) returns (bool success);
    function allowance(address _owner, address _spender) view returns (uint256 remaining);
    
    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
    
}

erc20.sol

pragma solidity ^0.4.20;
//引入接口文件
import './erc20interface.sol';

contract ERC20 is ERC20Interface{
    
    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) allowed;
    
    constructor(string _name) public{
        name = _name;  //"UpChain";
        symbol = "UPT";
        decimals = 0;
        totalSupply = 1000000;
    }
    
    function transfer(address _to, uint256 _value) returns (bool success) {
        
        require(_to != address(0));
        require(balanceOf[msg.sender] >= _value);
        require(balanceOf[_to] + _value >= balanceOf[_to]);
        
        balanceOf[msg.sender] -= _value;
        balanceOf[_to] += _value;
        
        emit Transfer(msg.sender, _to, _value);
        
        return true;
    }
    
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        
        require(_to != address(0));
        require(allowed[_from][msg.sender] >= _value);
        require(balanceOf[_from] >= _value);
        require(balanceOf[_to] + _value >= balanceOf[_to]);
        
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        
        allowed[_from][msg.sender] -= _value;
        emit Transfer(msg.sender, _to, _value);
        
        return true;
    }
    
    function approve(address _spender, uint256 _value) returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        
        emit Approval(msg.sender, _spender, _value);
        
        return true;
    }
    
    function allowance(address _owner, address _spender) view returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }
    
}