a very simple code of an ERC20 token

simpleERC20Token.sol

// contracts/SimpleToken.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
 
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
 
/**
* @title SimpleToken
* @dev Very simple ERC20 Token example, where all tokens are pre-assigned to the creator.
* Note they can later distribute these tokens as they wish using `transfer` and other
* `ERC20` functions.
* Based on https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.5.1/contracts/examples/SimpleToken.sol
*/
contract SimpleToken is ERC20 {
   /**
    * @dev Constructor that gives msg.sender all of existing tokens.
    */
   constructor(
       string memory name,
       string memory symbol,
       uint256 initialSupply
   ) public ERC20(name, symbol) {
       _mint(msg.sender, initialSupply);
   }
}