ERC20 note

erc20.sol

pragma solidity ^0.6.0;

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes calldata _extraData) external; }

contract TokenERC20 {
   string public name;
   string public symbol;
   uint8 public decimals = 18;
   uint256 public totalSupply;

   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);
   event Burn(address indexed from, uint256 value);

   constructor(
       uint256 initialSupply,
       string memory tokenName,
       string memory tokenSymbol
   ) public {
       totalSupply = initialSupply * 10 ** uint256(decimals);
       balanceOf[msg.sender] = totalSupply;
       name = tokenName;
       symbol = tokenSymbol;
   }

   function _transfer(address _from, address _to, uint _value) internal {
       require(_to != address(0));
       require(balanceOf[_from] >= _value);
       require(balanceOf[_to] + _value >= balanceOf[_to]);
       uint 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 transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
       require(_value <= allowance[_from][msg.sender]);     // Check allowance
       allowance[_from][msg.sender] -= _value;
       _transfer(_from, _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 approveAndCall(address _spender, uint256 _value, bytes memory _extraData)
       public
       returns (bool success) {
       tokenRecipient spender = tokenRecipient(_spender);
       if (approve(_spender, _value)) {
           spender.receiveApproval(msg.sender, _value, address(this), _extraData);
           return true;
       }
   }

   function burn(uint256 _value) public returns (bool success) {
       require(balanceOf[msg.sender] >= _value);
       balanceOf[msg.sender] -= _value;
       totalSupply -= _value;
       emit Burn(msg.sender, _value);
       return true;
   }

   function burnFrom(address _from, uint256 _value) public returns (bool success) {
       require(balanceOf[_from] >= _value);
       require(_value <= allowance[_from][msg.sender]);
       balanceOf[_from] -= _value;
       allowance[_from][msg.sender] -= _value;
       totalSupply -= _value;
       emit Burn(_from, _value);
       return true;
   }
}

// Copied from https://hide.ac/articles/Wg_HYcCYq

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