A sample crowdfunding app using solidity

FundMe.sol

// // SPDX-License-Identifier: MIT
pragma solidity >=0.6.6 <0.9.0;

import "@chainlink/contracts/src/v0.6/interfaces/AggregatorV3Interface.sol";
import "@chainlink/contracts/src/v0.6/vendor/SafeMathChainlink.sol";


contract FundMe {
    using SafeMathChainlink for uint256;
    address public owner;
    address[] public funders;

    constructor() public {
        owner = msg.sender;
    }

    mapping(address => uint256) public addressToAmountFunded;

    function fund() public payable {
        uint256 minimumUSD = 20 * 10 ** 18;
        require(getConversionRate(msg.value) >= minimumUSD, "You need to spend more ETH!");
        addressToAmountFunded[msg.sender] += msg.value;
        funders.push(msg.sender);
    }

    function getVersion() public view returns (uint256){
        AggregatorV3Interface priceFeed = AggregatorV3Interface(0x9326BFA02ADD2366b30bacB125260Af641031331);
        return priceFeed.version();
    }

    function getPrice() public view returns (uint256){
        AggregatorV3Interface priceFeed = AggregatorV3Interface(0x9326BFA02ADD2366b30bacB125260Af641031331);
        (,int256 answer,,,) = priceFeed.latestRoundData();
        return uint256(answer * 10000000000);
    }

    function getConversionRate(uint256 ethAmount) public view returns (uint256){
        uint256 ethPrice = getPrice();
        uint256 ethAmountInUsd = (ethPrice * ethAmount) / 1000000000000000000;
        // the actual ETH/USD conversation rate, after adjusting the extra 0s.
        return ethAmountInUsd;
    }

    modifier onlyOwner {
       require(msg.sender == owner);
       _;
    }

    function withdraw() payable onlyOwner public {
        msg.sender.transfer(address(this).balance);
        for (uint256 funderIndex=0; funderIndex < funders.length; funderIndex++){
            address funder = funders[funderIndex];
            addressToAmountFunded[funder] = 0;
        }

        funders = new address[](0);
    }
}