Solidity exercise: projects loans contract

BitCrowdFunding.sol

pragma solidity ^0.4.18;

contract owned {
    function owned() public { owner = msg.sender; }
    address owner;

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

contract BitCrowdFunding is owned {
    
    User[] crowd;
    Project[] projects;
    
    struct User {
        address wallet;
    }
    
    struct Project {
        uint id;
        string name;
        address wallet;
        bool approved;
        address owner;
        mapping (address => uint) pendingWithdrawals; // withdrawal pattern
    }

    modifier membersOnly {
        for(uint i = 0; i < crowd.length; i++) {
            if(crowd[i].wallet == msg.sender) {
                _;
                break;
            }
        }
    }
    
    modifier newcomers {
        for(uint i = 0; i < crowd.length; i++) {
            if(crowd[i].wallet == msg.sender) {
                return;
            }
        }
        _;
    }
    
    modifier ownsProject {
        for(uint i = 0; i < projects.length; i++) {
            if(projects[i].owner == msg.sender) {
                _;
                break;
            }
        }
    }
    
    function BitCrowdFunding() public {
        joinIn();
    }
    
    function joinIn() public newcomers {
        crowd.push( User({wallet: msg.sender}) );
    }

    function loan(uint project_id) public membersOnly payable {
        for(uint i = 0; i < projects.length; i++) {
            if(projects[i].id == project_id && projects[i].approved) {
                projects[i].pendingWithdrawals[msg.sender] += msg.value;
                break;
            }
        }
    }
    
    function withdrawLoans(uint project_id) public ownsProject {
        for(uint i = 0; i < projects.length; i++) {
            if(projects[i].id == project_id) {
                uint amount = projects[i].pendingWithdrawals[msg.sender];
                projects[i].pendingWithdrawals[msg.sender] = 0;
                msg.sender.transfer(amount);
                break;
            }
        }
    }
    
    /**
     * @return uint Project unique ID
     * */
    function addProject(string name, address wallet) public membersOnly returns(uint) {
        uint id = projects.length+1;
        projects.push(Project({
            id: id,
            name: name,
            wallet: wallet,
            owner: msg.sender,
            approved: false
        }));
        
        return id;
    }
    
    /**
     * Only owner can do this
     * */
    function approveProject(uint id) public onlyOwner returns(bool) {
        for(uint i = 0; i < projects.length; i++) {
            if(projects[i].id == id) {
                projects[i].approved = true;
                return true;
            }
        }
        return false;
    }
}