pragma solidity ^0.4.11;

contract EXA {
    string public constant symbol = "EXA.COM";
    string public constant name = "example.com";
    uint8 public constant decimals = 18;
    uint256 _totalSupply = (10 ** 8) * (10 ** 18);

    address public owner;

    // Balances for each account
    mapping(address => uint256) balances;
    // Owner of account approves the transfer of an amount to another account
    mapping(address => mapping (address => uint256)) allowed;

    // Constructor
    function EXA() public {
        owner = msg.sender;
        balances[owner] = _totalSupply;
    }

    // Send back ether sent to me
    function () public {
        revert();
    }

    function totalSupply() constant public returns (uint256) {
        return _totalSupply;
    }

    // What is the balance of a particular account?
    function balanceOf(address _owner) constant public returns (uint256 balance) {
        return balances[_owner];
    }

    // Transfer the balance from owner's account to another account
    function transfer(address _to, uint256 _amount) public returns (bool success) {
        if (balances[msg.sender] >= _amount && _amount > 0 && balances[_to] + _amount > balances[_to]) {
            balances[msg.sender] -= _amount;
            balances[_to] += _amount;
            Transfer(msg.sender, _to, _amount);
            return true;
        } else {
            return false;
        }
    }

    // Send _value amount of tokens from address _from to address _to
    // The transferFrom method is used for a withdraw workflow, allowing contracts to send
    // tokens on your behalf, for example to "deposit" to a contract address and/or to charge
    // fees in sub-currencies; the command should fail unless the _from account has
    // deliberately authorized the sender of the message via some mechanism; we propose
    // these standardized APIs for approval:
    function transferFrom(address _from, address _to, uint256 _amount) public returns (bool success) {
        if (balances[_from] >= _amount && allowed[_from][msg.sender] >= _amount && _amount > 0 && balances[_to] + _amount > balances[_to]) {
            balances[_from] -= _amount;
            allowed[_from][msg.sender] -= _amount;
            balances[_to] += _amount;
            Transfer(_from, _to, _amount);
            return true;
        } else {
            return false;
        }
    }

    // Allow _spender to withdraw from your account, multiple times, up to the _value amount.
    // If this function is called again it overwrites the current allowance with _value.
    function approve(address _spender, uint256 _amount) public returns (bool success) {
        allowed[msg.sender][_spender] = _amount;
        Approval(msg.sender, _spender, _amount);
        return true;
    }

    // Returns the amount which _spender is still allowed to withdraw from _owner
    function allowance(address _owner, address _spender) constant public returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}