Defining and implementing the ERC-20 interface

The ERC-20 interface defines a set of rules that a token must follow in order to be traded on the Ethereum network. There are a total of six mandatory functions and three optional functions that a token contract must implement. We define the ERC-20 token interface as follows. MyERC20Token will implement the ERC-20 interface:

interface ERC20 {
    function transfer(address to, uint256 value) external returns (bool);
    function approve(address spender, uint256 value) external returns (bool);
    function transferFrom(address from, address to, uint256 value) external returns (bool);
    function totalSupply() external view returns (uint256);
    function balanceOf(address who) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);
   &...