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ERC20.sol

pragma solidity ^0.4.24;

import "./ERC20Basic.sol";


/**
 * @title ERC20 interface
 * @dev Enhanced interface with allowance functions.
 * See https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
    // Check the allowed value that the _owner allows the _spender to take from his balance.
    function allowance(address _owner, address _spender) public view returns (uint256);

    // Transfer _value from the balance of holder _from to the receiver _to.
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool);

    // Approve _spender to take some _value from the balance of msg.sender.
    function approve(address _spender, uint256 _value) public returns (bool);
    
    // Fired when an approval is made.
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}

ERC20Basic.sol

pragma solidity ^0.4.24;


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface.
 * See https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
    // Total supply of token.
    function totalSupply() public view returns (uint256);
    // Balance of a holder _who
    function balanceOf(address _who) public view returns (uint256);
    // Transfer _value from msg.sender to receiver _to.
    function transfer(address _to, uint256 _value) public returns (bool);
    // Fired when a transfer is made
    event Transfer(
        address indexed from, 
        address indexed to, 
        uint256 value
    );
}

SafeMath.sol

pragma solidity ^0.4.24;


/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {
    /**
    * @dev Multiplies two numbers, throws on overflow.
    */
    function mul(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
      // Gas optimization: this is cheaper than asserting 'a' not being zero, but the
      // benefit is lost if 'b' is also tested.
      // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (_a == 0) {
            return 0;
        }

        c = _a * _b;
        assert(c / _a == _b);
        return c;
    }

    /**
    * @dev Integer division of two numbers, truncating the quotient.
    */
    function div(uint256 _a, uint256 _b) internal pure returns (uint256) {
        // assert(_b > 0); // Solidity automatically throws when dividing by 0
        // uint256 c = _a / _b;
        // assert(_a == _b * c + _a % _b); // There is no case in which this doesn't hold
        return _a / _b;
    }

    /**
    * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
        assert(_b <= _a);
        return _a - _b;
    }

    /**
    * @dev Adds two numbers, throws on overflow.
    */
    function add(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
        c = _a + _b;
        assert(c >= _a);
        return c;
    }
}

TicTalk.sol

pragma solidity ^0.4.24;

import "./ERC20.sol";
import "./SafeMath.sol";

/**
 * @title TicTalk Token Contract
 * @dev TicTalk Foundation token release contract. Compatible with ERC20/VIP180 Standard.
 * Special thanks go to openzeppelin-solidity project.
 */
contract TicTalk is ERC20 {
    using SafeMath for uint256;

    // Name of token
    string public constant name = "TicTalk Token";
    // Symbol of token
    string public constant symbol = "TIC";
    // Decimals of token
    uint8 public constant decimals = 18;
    // Total supply of the tokens
    uint256 internal totalSupply_;

    // balances: (_holder => _value)
    mapping(address => uint256) public balances;

    // allowed: (_owner, => (_spender, _value))
    mapping (address => mapping (address => uint256)) internal allowed;

    constructor() public {
        totalSupply_ = 1 * (10 ** 10) * (10 ** 18); // 10 000 000 000 tokens of 18 decimals.
        balances[msg.sender] = totalSupply_;
        emit Transfer(0, msg.sender, totalSupply_);  // init mint of coins complete.
    }

    // Get the total supply of the coins
    function totalSupply() public view returns (uint256) {
        return totalSupply_;
    }

    // Get the balance of _owner
    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balances[_owner];
    }

    /** Make a Transfer.
     * @dev This operation will deduct the msg.sender's balance.
     * @param _to address The address the funds go to.
     * @param _value uint256 The amount of funds.
    */
    function transfer(address _to, uint256 _value) public returns (bool) {
        require(_to != address(0), "Cannot send to all zero address.");
        require(_value <= balances[msg.sender], "msg.sender balance is not enough.");

        // SafeMath.sub will throw if there is not enough balance.
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    /**
     * @dev Check the allowed funds that _spender can take from _owner.
     * @param _owner address The address which owns the funds.
     * @param _spender address The address which will spend the funds.
     * @return A uint256 specifying the amount of tokens still available for the spender.
    */
    function allowance(address _owner, address _spender) public view returns (uint256) {
        return allowed[_owner][_spender];
    }
    
    /**
     * @dev Transfer tokens from one address to another
     * @param _from address The address which you want to send tokens from
     * @param _to address The address which you want to transfer to
     * @param _value uint256 the amount of tokens to be transferred
    */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        require(_value <= balances[_from], "_from doesnt have enough balance.");
        require(_value <= allowed[_from][msg.sender], "Allowance of msg.sender is not enough.");
        require(_to != address(0), "Cannot send to all zero address.");

        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        emit Transfer(_from, _to, _value);
        return true;
    }

    /**
     * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
     * @param _spender The address which will spend the funds.
     * @param _value The amount of tokens to be spent.
    */
    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
}