gistfile1.txt

pragma solidity ^0.6.4;

contract Token {
    ...
    ...

    mapping(address => uint) public balanceOf;
    event Transfer(address indexed _from, address indexed _to, uint256 _value);

    
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }
    
    function transfer(address _to, uint _value) public returns (bool success) {

        require(_to != address(0));
        require(balanceOf[msg.sender] >= _value);

        balanceOf[msg.sender] = sub(balanceOf[_to], _value);
        balanceOf[_to] = add(balanceOf[_to], _value);

        emit Transfer(msg.sender, _to, _value);

        return true;
    } 

}