CrowdFunding Dapp

CrowdFunding.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract CrowdFunding {

    uint public minContribution;
    uint public deadline;
    uint public target;
    uint public raiseAmount;
    uint public noOfContributors;
    mapping(address => uint) public contributors;

    constructor(uint _target, uint _expireAfter) {
        minContribution = 100 wei;
        target = _target;
        deadline = block.timestamp + _expireAfter;

    }

    function sendEth () payable public {
        require(msg.value > minContribution, "Minimum contributon not met.");
        require(block.timestamp < deadline, "Deadline has been passed.");
        if(contributors[msg.sender] == 0) {
            noOfContributors++;
        }
        contributors[msg.sender] += msg.value;
        raiseAmount += msg.value;

    }

    function refund() public {
        require(block.timestamp > deadline);
        require(contributors[msg.sender] > 0);
        address payable user = payable(msg.sender);
        uint value = contributors[msg.sender];
        user.transfer(value);
        contributors[msg.sender] = 0;
        raiseAmount -= value;
        noOfContributors--;
    }

    function getBalance() public view returns(uint) {
        return address(this).balance;
    }
}