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ballot.sol

pragma solidity >=0.4.22 <0.6.0;
contract Ballot {

    struct Voter {
        uint weight;
        bool voted;
        uint8 vote;
        address delegate;
    }
    struct Proposal {
        uint voteCount;
    }

    address chairperson;
    mapping(address => Voter) voters;
    Proposal[] proposals;

    /// Create a new ballot with $(_numProposals) different proposals.
    constructor(uint8 _numProposals) public {
        chairperson = msg.sender;
        voters[chairperson].weight = 1;
        proposals.length = _numProposals;
    }

    /// Give $(toVoter) the right to vote on this ballot.
    /// May only be called by $(chairperson).
    function giveRightToVote(address toVoter) public {
        if (msg.sender != chairperson || voters[toVoter].voted) return;
        voters[toVoter].weight = 1;
    }

    /// Delegate your vote to the voter $(to).
    function delegate(address to) public {
        Voter storage sender = voters[msg.sender]; // assigns reference
        if (sender.voted) return;
        while (voters[to].delegate != address(0) && voters[to].delegate != msg.sender)
            to = voters[to].delegate;
        if (to == msg.sender) return;
        sender.voted = true;
        sender.delegate = to;
        Voter storage delegateTo = voters[to];
        if (delegateTo.voted)
            proposals[delegateTo.vote].voteCount += sender.weight;
        else
            delegateTo.weight += sender.weight;
    }

    /// Give a single vote to proposal $(toProposal).
    function vote(uint8 toProposal) public {
        Voter storage sender = voters[msg.sender];
        if (sender.voted || toProposal >= proposals.length) return;
        sender.voted = true;
        sender.vote = toProposal;
        proposals[toProposal].voteCount += sender.weight;
    }

    function winningProposal() public view returns (uint8 _winningProposal) {
        uint256 winningVoteCount = 0;
        for (uint8 prop = 0; prop < proposals.length; prop++)
            if (proposals[prop].voteCount > winningVoteCount) {
                winningVoteCount = proposals[prop].voteCount;
                _winningProposal = prop;
            }
    }
}

ballot_test.sol

import "remix_tests.sol"; // this import is automatically injected by Remix.
import "./ballot.sol";

contract test3 {
   
    Ballot ballotToTest;
    function beforeAll () public {
       ballotToTest = new Ballot(2);
    }
    
    function checkWinningProposal () public {
        ballotToTest.vote(1);
        Assert.equal(ballotToTest.winningProposal(), uint(1), "1 should be the winning proposal");
    }
    
    function checkWinninProposalWithReturnValue () public view returns (bool) {
        return ballotToTest.winningProposal() == 1;
    }
}

Course.sol

pragma solidity 0.5.1;

contract Course {
    
    address payable admin; //School Administrator
    address payable ManagerContract;
    address instructor;
    int courseNo;
    
    struct Marks{
        int midsem;
        int endsem;
        int attendance;
    }
    
    mapping (int => Marks) student;
    mapping (int => bool) isEnrolled;
    
    modifier onlyOwner{
        require(msg.sender == admin);
        _;
    }
    
    constructor(int c, address inst, address payable adm) public {

        courseNo = c; // Initializing course Number
        instructor = inst; // Initializing Instructor address
        admin = adm; // Initializing School Administrator
        ManagerContract = 0xCA35b7d915458EF540aDe6068dFe2F44E8fa733c;
    }
    
    function kill() public onlyOwner {
        //The admin has the right to kill the contract at any time.
        //Take care that no one else is able to kill the contract
            selfdestruct(admin);
    }
    
    function enroll(int rollNo) public {
        //This function can only be called by the ManagerContract
        //Enroll a student in the course if not already registered
        if(msg.sender == admin){
            if(isEnrolled[rollNo] == false){
                student[rollNo].midsem = 0;
                student[rollNo].endsem = 0;
                student[rollNo].attendance = 0;
                isEnrolled[rollNo] = true;
            }
        }
    }
    
    function markAttendance(int rollNo) public{
        //Only the instructor can mark the attendance
        //Increment the attendance variable by one
        //Make sure the student is enrolled in the course
        if(msg.sender == instructor){
            if(isEnrolled[rollNo]==true){
                student[rollNo].attendance++;
            }
        }
    }
    
    function addMidSemMarks(int rollNo, int marks) public{
        //Only the instructor can add midsem marks
        //Make sure that the student is enrolled in the course
        if(msg.sender == instructor){
            if(isEnrolled[rollNo]==true){
                student[rollNo].midsem = marks;
            }
        }
    }
    
    function addEndSemMarks(int rollNo, int marks) public{
        //Only the instructor can add endsem marks
        //Make sure that the student is enrolled in the course
        if(msg.sender == instructor){
            if(isEnrolled[rollNo]==true){
                student[rollNo].endsem = marks;
            }
        }
    }
    
    function getMidsemMarks(int rollNo) public view returns(int) {
        //Can only be called by the ManagerContract
        //return the midSem, endSem and attendance of the student
        //Make sure to check the student is enrolled
        if(msg.sender == admin && isEnrolled[rollNo]==true){
            return student[rollNo].midsem;
        }

    }
    
    function getEndsemMarks(int rollNo) public view returns(int) {
        //Can only be called by the ManagerContract
        //return the midSem, endSem and attendance of the student
        //Make sure to check the student is enrolled
        if(msg.sender == admin && isEnrolled[rollNo]==true){
            return student[rollNo].endsem;
        }

    }
    
    function getAttendance(int rollNo) public view returns(int) {
        //Can only be called by the ManagerContract
        //return the midSem, endSem and attendance of the student
        //Make sure to check the student is enrolled
        if(msg.sender == admin && isEnrolled[rollNo]==true){
            return student[rollNo].attendance;
        }
    }
    
    function isEnroll(int rollNo) public view returns(bool){
        //Returns if a roll no. is enrolled in a particular course or not
        //Can be accessed by anyone
        if(isEnrolled[rollNo]==true){
            return true;
        }
        else{
            return false;
        }

    }
    
}

hello.sol

pragma solidity >0.4.16;

contract HelloWorld {
    
    uint256 public rollno = 18111000;
    mapping (uint => Student) public students;
    address admin;
    address payable wallet;
    mapping (address => uint256) public balances;
    
    struct Student{
        uint _id;
        string _firstname;
        string _lastname;
    }
    
    modifier onlyOwner(){
        require(msg.sender == admin);
        _;
    }
    
    event Purchase(
        address indexed _buyer,
        uint256 _amount
    );
        
    
    constructor(address payable _wallet) public {
        admin = msg.sender;
        wallet = _wallet;
    }
    
    function buyToken() public payable {
        // Buy a Token 
        balances[msg.sender] += 1;
        // also send ether to wallet.
        wallet.transfer(msg.value);
        emit Purchase(msg.sender, 1);
    }
    
    //Fallback function - can be called from outside contract only
    function() external payable {
        buyToken();
    }
    
    /* function addStudent
    (
        string memory _firstname, 
        string memory _lastname 
    )    
        public 
        onlyOwner
    {
        rollno += 1;
        students[rollno] = Student(rollno, _firstname, _lastname);
    }
    */
}

Manager.sol

pragma solidity 0.5.1;
import "./Course.sol";

contract Manager {
    //Address of the school administrator
    address payable admin;
    
    mapping (address => int) student;
    mapping (address => bool) isStudent;
    mapping (int => bool) isCourse;
    mapping (int => Course) course;
    
    int rollCount = 19111000;
    
    //Constructor
    constructor() public {
        //Initialising Manager 
        admin = 0xCA35b7d915458EF540aDe6068dFe2F44E8fa733c;
    }
    
    
    function kill() public{
        //The admin has the right to kill the contract at any time.
        //Take care that no one else is able to kill the contract
        require(msg.sender == admin);
        if(msg.sender == admin) {
            selfdestruct(admin);
        }
    }
    
    function addStudent() public{
        //Anyone on the network can become a student if not one already
        //Remember to assign the new student a unique roll number
        if(isStudent[msg.sender] == false){
            student[msg.sender] = rollCount;
            rollCount += 1;
            isStudent[msg.sender] = true;
        }
    }
    
    function addCourse(int courseNo, address instructor) public{
	//Add a new course with course number as courseNo, and instructor at address instructor
    //Note that only the admin can add a new course. Also, don't create a new course if course already exists
    require(msg.sender == admin);
        if(msg.sender == admin){
            if(isCourse[courseNo] == false){
                course[courseNo] = new Course(courseNo, instructor, admin);
            }
        }
    }
    
    function regCourse(int courseNo) public{
        //Register the student in the course if he is a student on roll and the courseNo is valid
        if (isCourse[courseNo] == true && isStudent[msg.sender]==true){
            course[courseNo].enroll(student[msg.sender]);
        }
    }
    
    function getMyMarks(int courseNo) public view returns(int, int, int) {
        //Check the courseNo for validity
        //Should only work for valid students of that course
	    //Returns a tuple (midsem, endsem, attendance)
	   // if(isStudent[msg.sender]==true){
	   //     int roll = student[msg.sender];
	   // }
        if (isCourse[courseNo] == true){
            if(course[courseNo].isEnroll(student[msg.sender]) == true){
                int r1 = course[courseNo].getMidsemMarks(student[msg.sender]);
                int r2 = course[courseNo].getEndsemMarks(student[msg.sender]);
                int r3 = course[courseNo].getAttendance(student[msg.sender]);
                return (r1, r2, r3);
            }
        }
    }
    
    function getMyRollNo() public view returns(int) {
        //Utility function to help a student if he/she forgets the roll number
        //Should only work for valid students
	//Returns roll number as int
    	if(isStudent[msg.sender] == true){
    	    return student[msg.sender];
    	}
        else{
            return -1;
        }
    }
    
}

part-b.abi

[
	{
		"constant": true,
		"inputs": [],
		"name": "greeter",
		"outputs": [
			{
				"name": "",
				"type": "string"
			}
		],
		"payable": false,
		"stateMutability": "pure",
		"type": "function"
	},
	{
		"constant": false,
		"inputs": [
			{
				"name": "rollNo",
				"type": "int256"
			}
		],
		"name": "addMe",
		"outputs": [],
		"payable": false,
		"stateMutability": "nonpayable",
		"type": "function"
	},
	{
		"constant": true,
		"inputs": [
			{
				"name": "rollNo",
				"type": "int256"
			}
		],
		"name": "myAnswer",
		"outputs": [
			{
				"name": "",
				"type": "bytes32"
			}
		],
		"payable": false,
		"stateMutability": "pure",
		"type": "function"
	},
	{
		"inputs": [],
		"payable": false,
		"stateMutability": "nonpayable",
		"type": "constructor"
	}
]