An ERC-20 Ethereum Token.

Token.sol

pragma solidity ^0.4.18;

import 'zeppelin-solidity/contracts/math/SafeMath.sol';

/**
 * Token
 *
 * @title A fixed supply ERC20 token contract.
 * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md
 */
contract Token {
    using SafeMath for uint;

    event Transfer(
        address indexed _from,
        address indexed _to,
        uint256 _value
    );

    event Approval(
        address indexed _owner,
        address indexed _spender,
        uint256 _value
    );

    string public symbol;
    string public name;
    uint8 public decimals;
    uint public totalSupply;

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

    /**
     * Constructs the Token contract and gives all of the supply to the address
     *     that deployed it. The fixed supply is 1 billion tokens with up to 18
     *     decimal places.
     */
    function Token() public {
        symbol = 'TOK';
        name = 'Token';
        decimals = 18;
        totalSupply = 1000000000 * 10**uint(decimals);
        balances[msg.sender] = totalSupply;
        Transfer(address(0), msg.sender, totalSupply);
    }

    /**
     * @dev Fallback function
     */
    function() public payable { revert(); }

    /**
     * Gets the token balance of any wallet.
     * @param _owner Wallet address of the returned token balance.
     * @return The balance of tokens in the wallet.
     */
    function balanceOf(address _owner)
        public
        constant
        returns (uint balance)
    {
        return balances[_owner];
    }

    /**
     * Transfers tokens from the sender's wallet to the specified `_to` wallet.
     * @param _to Address of the transfer's recipient.
     * @param _value Number of tokens to transfer.
     * @return True if the transfer succeeded, false if not.
     */
    function transfer(address _to, uint _value) public returns (bool success) {
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        Transfer(msg.sender, _to, _value);
        return true;
    }

    /**
     * Transfer tokens from any wallet to the `_to` wallet. This only works if
     *     the `_from` wallet has already allocated tokens for the caller keyset
     *     using `approve`. From wallet must have sufficient balance to
     *     transfer. Caller must have sufficient allowance to transfer.
     * @param _from Wallet address that tokens are withdrawn from.
     * @param _to Wallet address that tokens are deposited to.
     * @param _value Number of tokens transacted.
     * @return True if the transfer succeeded, false if not.
     */
    function transferFrom(address _from, address _to, uint _value)
        public
        returns (bool success)
    {
        balances[_from] = balances[_from].sub(_value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        Transfer(_from, _to, _value);
        return true;
    }

    /**
     * Sender allows another wallet to `transferFrom` tokens from their wallet.
     * @param _spender Address of `transferFrom` recipient.
     * @param _value Number of tokens to `transferFrom`.
     * @return True if the approval succeeded, false if not.
     */
    function approve(address _spender, uint _value)
        public
        returns (bool success)
    {
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }

    /**
     * Gets the number of tokens that a `_owner` has approved for a _spender
     *     to `transferFrom`.
     * @param _owner Wallet address that tokens can be withdrawn from.
     * @param _spender Wallet address that tokens can be deposited to.
     * @return The number of tokens allowed to be transferred.
     */
    function allowance(address _owner, address _spender)
        public
        constant
        returns (uint remaining)
    {
        return allowed[_owner][_spender];
    }
}