pragma solidity ^0.4.24;


/*Token contract based on Zeppelin StandardToken contract*/

library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    assert(c / a == b);
    return c;
  }

  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 c;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}

/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * See https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender)
    public view returns (uint256);

  function transferFrom(address from, address to, uint256 value)
    public returns (bool);

  function approve(address spender, uint256 value) public returns (bool);
  event Approval(
    address indexed owner,
    address indexed spender,
    uint256 value
  );
}
contract StandardToken is ERC20 {
  using SafeMath for uint;
     
    string internal _name;
    string internal _symbol;
    uint8 internal _decimals;
    uint256 internal _totalSupply;

    mapping (address => uint256) internal balances;
    mapping (address => mapping (address => uint256)) internal allowed;

    constructor() public {
        _symbol = "ExShares";
        _name = "EXS";
        _decimals = 18;
        _totalSupply = 100 * (uint256(10)**_decimals);
        balances[msg.sender] = _totalSupply;
    }

    function name()
        public
        view
        returns (string) {
        return _name;
    }

    function symbol()
        public
        view
        returns (string) {
        return _symbol;
    }

    function decimals()
        public
        view
        returns (uint8) {
        return _decimals;
    }

    function totalSupply()
        public
        view
        returns (uint256) {
        return _totalSupply;
    }

   function transfer(address _to, uint256 _value) public returns (bool) {
     require(_to != address(0));
     require(_value <= balances[msg.sender]);
     balances[msg.sender] = SafeMath.sub(balances[msg.sender], _value);
     balances[_to] = SafeMath.add(balances[_to], _value);
     emit Transfer(msg.sender, _to, _value);
     return true;
   }

  function balanceOf(address _owner) public view returns (uint256 balance) {
    return balances[_owner];
   }

  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
     require(_value <= balances[_from]);
     require(_value <= allowed[_from][msg.sender]);

    balances[_from] = SafeMath.sub(balances[_from], _value);
     balances[_to] = SafeMath.add(balances[_to], _value);
     allowed[_from][msg.sender] = SafeMath.sub(allowed[_from][msg.sender], _value);
    emit Transfer(_from, _to, _value);
     return true;
   }

   function approve(address _spender, uint256 _value) public returns (bool) {
     allowed[msg.sender][_spender] = _value;
     emit Approval(msg.sender, _spender, _value);
     return true;
   }

  function allowance(address _owner, address _spender) public view returns (uint256) {
     return allowed[_owner][_spender];
   }

   function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
     allowed[msg.sender][_spender] = SafeMath.add(allowed[msg.sender][_spender], _addedValue);
     emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
     return true;
   }

  function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
     uint oldValue = allowed[msg.sender][_spender];
     if (_subtractedValue > oldValue) {
       allowed[msg.sender][_spender] = 0;
     } else {
       allowed[msg.sender][_spender] = SafeMath.sub(oldValue, _subtractedValue);
    }
     emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
     return true;
   }

}