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pragma solidity >=0.4.16 <0.9.0;

contract HelloWorld {
    string public message = "Hello World!";
}

pragma solidity ^0.8.10;

contract HelloWorld {
    string message = "Hello world!";

    function set(string memory _msg) public {
        message = _msg;
    }

    function get() public view returns (string memory) {
        return message;
    }
}

pragma solidity ^0.8.10;

contract Example {
    function globalVariables() {
        address payable sender = msg.sender;
        uint256 value = msg.value;
        bytes data = msg.data;
    }
}

interface ERC20 {
  function totalSupply() external view returns (uint);
  function balanceOf(address who) external view returns (uint);
  function transfer(address to, uint value) external returns (bool);
  function allowance(address owner, address spender) external view returns (uint);
  function transferFrom(address from, address to, uint value) external returns (bool);
  function approve(address spender, uint value) external returns (bool);
  
  event Approval(address indexed owner, address indexed spender, uint value);  
  event Transfer(address indexed from, address indexed to, uint value);
}

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract GLDToken is ERC20, Ownable {
    constructor(uint256 initialSupply) ERC20("Gold", "GLD") {
        _mint(msg.sender, initialSupply);
    }
    function mint(address to, uint256 amount) public onlyOwner {
        _mint(to, amount);
    }
}

# Setup
> npm install @openzeppelin/contracts
> npx hardhat compile
> npx hardhat node

# Deploy
> npx hardhat run --network localhost deploy.js

# Stop
> npx hardhat clean

// scripts/deploy.js

const GLDToken = await ethers.getContractFactory("GLDToken");

// execute transaction
const token = await GLDToken.deploy('1000');

// wait for transaction to be part of the blockchain
await token.deployed();

// GLDToken.js

const token = await ethers.getContractAt("GLDToken", player);
await token.balanceOf(player);
// 10

await token.transfer(defenseOftheAncients2, 3);
await token.balanceOf(player);
// 7