ERC20 Token Exchange

TokenExchange.sol

pragma solidity 0.4.24;

interface IERC20 {
  function totalSupply() external view returns (uint256);
  function balanceOf(address who) external view returns (uint256);
  function transfer(address to, uint256 value) external returns (bool);
  function transferFrom(address from, address to, uint256 value) external returns (bool);
}

contract ERC20Exchange {

  address myToken;
  address yourToken;

  constructor(address _myToken) public {
    myToken = _myToken;
  }

  function tradeToken(address _yourToken) public {
    yourToken = _yourToken;
    require(IERC20(yourToken).totalSupply() == 10, "Your token needs to have a total supply of 10");
    //Transfer mytoken to you
    require(IERC20(myToken).transfer(msg.sender, 10));
    require(IERC20(yourToken).transferFrom(msg.sender, address(this), 10));
  }

  function check(address player) public view returns (bool, uint) {
    require(IERC20(yourToken).totalSupply() == 10, "Your token needs to have a total supply of 10");
    require(IERC20(myToken).balanceOf(player) == 10);
    require(IERC20(yourToken).balanceOf(player) == 10);
    return (true, 400);
  }

}