// SPDX-License-Identifier: MIT
pragma solidity >=0.4.11 <0.9.0;
contract CrowdFunding {// 定义的新类型包含两个属性。struct Funder {address addr;uint amount;}struct Campaign {address payable  beneficiary;uint fundingGoal;uint numFunders;uint amount;mapping (uint => Funder) funders;}uint numCampaigns;mapping (uint => Campaign)   campaigns;function newCampaign(address beneficiary, uint goal) public  returns (uint ) {uint campaignID = numCampaigns++; Campaign storage c = campaigns[campaignID];c.beneficiary=payable(beneficiary);c.fundingGoal=goal;c.amount=0;c.numFunders=0;return campaignID;}function contribute(uint campaignID) public payable   {Campaign storage c = campaigns[campaignID];c.funders[c.numFunders++] = Funder({addr: msg.sender, amount: msg.value});c.amount += msg.value;}function checkGoalReached(uint campaignID) public    returns (bool reached) {Campaign storage c = campaigns[campaignID];if (c.amount < c.fundingGoal)return false;uint amount = c.amount;c.amount = 0;c.beneficiary.transfer(amount);return true;}function info(uint campaignID) public view returns(uint){Campaign storage c = campaigns[campaignID];uint amount = c.amount;return amount;}
}

Remix - Ethereum IDE