benchmark1/integer overflow/566.sol

pragma solidity ^0.4.21;
contract Token{
    uint256 public totalSupply;

    function balanceOf(address _owner) public constant returns (uint256 balance);
    function transfer(address _to, uint256 _value) public returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
    function approve(address _spender, uint256 _value) public returns (bool success);
    function allowance(address _owner, address _spender) public constant returns (uint256 remaining);

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}

contract CYFToken is Token {

    string public name = "ÆòÁ¦ÂíÔúÂÞµÄÑ©CYF";                   
    uint8 public decimals = 18;               
    string public symbol = "CYF";               

    mapping (address => uint256) balances;
    mapping (address => mapping (address => uint256)) allowed;

    function CYFToken() public {
        totalSupply = 7000000000 * (10 ** (uint256(decimals)));         
        balances[msg.sender] = totalSupply; 
    }

    function transfer(address _to, uint256 _value) public returns (bool success) {
        
        
        require(balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]);
        require(_to != 0x0);
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        emit Transfer(msg.sender, _to, _value);
        return true;
    }
    function transferFrom(address _from, address _to, uint256 _value) public returns 
    (bool success) {
        require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value);
        balances[_to] += _value;
        balances[_from] -= _value; 
        allowed[_from][msg.sender] -= _value;
        emit Transfer(_from, _to, _value);
        return true;
    }
    function balanceOf(address _owner) public constant returns (uint256 balance) {
        return balances[_owner];
    }
    function approve(address _spender, uint256 _value) public returns (bool success)   
    { 
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    function allowance(address _owner, address _spender) public constant returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }
}