Notes

pragma solidity ^0.5.8;

contract TRC20 {
string public name = "TestToken";
string public symbol = "TT";
uint8 public decimals = 18;
uint256 public totalSupply = 1000000 * 10 ** uint256(decimals);
mapping (address => uint256) public balanceOf;
mapping (address => mapping (address => uint256)) public allowance;

event Transfer(address indexed from, address indexed to, uint256 value);
event Approval(address indexed owner, address indexed spender, uint256 value);

constructor() public {
balanceOf[msg.sender] = totalSupply;
}

function _transfer(address _from, address _to, uint256 _value) internal {
require(_to != address(0x0));
require(balanceOf[_from] >= _value);
require(balanceOf[_to] + _value >= balanceOf[_to]);

uint256 previousBalances = balanceOf[_from] + balanceOf[_to];
balanceOf[_from] -= _value;
balanceOf[_to] += _value;
emit Transfer(_from, _to, _value);

assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
}

function transfer(address _to, uint256 _value) public returns (bool success) {
_transfer(msg.sender, _to, _value);
return true;
}

function approve(address _spender, uint256 _value) public returns (bool success) {
allowance[msg.sender][_spender] = _value;
emit Approval(msg.sender, _spender, _value);
return true;
}

function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
require(_value <= allowance[_from][msg.sender]);
allowance[_from][msg.sender] -= _value;
_transfer(_from, _to, _value);
return true;
}
}