Solidity

Synopsis

Online voting needs results that nobody can quietly alter. A blockchain is a good fit: every vote is a transaction recorded permanently, and anyone can check that the count follows the published rules.

In this project the deploying account becomes the BlockAdmin (election administrator). The admin cannot change votes; the admin’s role is to view the total number of votes cast and to calculate and publish the winner.

Every other account acts as a voter. A voter casts a vote by calling the function of the chosen candidate (or NOTA). The contract records the voter’s address and rejects a second vote from the same address, so no one can vote twice.

Contract Architecture

How It Works

The result loop uses if (maxCount < candidate.voteCount), so in a tie the candidate with the lower code (declared earlier) remains the winner.

Key Requirements (Concepts Used)

• Struct – Candidate record (Chapter 13) declared at file level and imported (Chapter 2).
• Enum – candidate codes and type(candidateCode).max (Chapter 11).
• Mapping – code → Candidate (Chapter 12).
• Dynamic array – list of voters (Chapter 10).
• Functions, view functions and public getters (Chapter 15).
• Modifiers – admin and duplicate-vote checks (Chapter 22).
• Constructor and msg.sender (Chapters 14 and 17).

How to Run in Remix

1. In Remix, create contracts/CandidateMaster.sol and paste the CandidateMaster.sol resource file. The import path in the main file expects exactly this name and folder.
2. Create contracts/VotePanelContract.sol and paste the VotePanelContract.sol resource file.
3. Compile with a 0.8.x compiler and deploy VotePanel from the first account – it becomes BlockAdmin.
4. Switch to other accounts and click one candidate function per account. Try voting twice from one account to see the “already casted” error.
5. Switch back to the admin account, call voteCountAndResult(), then click winner and totalVotesCasted.

Limitations and Extension Exercises

Exercise solution (one possible approach)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract VotePanelV2 {
    enum Code { AJIT, ASHISH, MAYANK, KUNAL, NOTA }

    address public immutable admin = msg.sender;
    bool public votingOpen = true;
    mapping(address => bool) public hasVoted;     // O(1) duplicate check
    mapping(Code => uint) public votes;
    uint public totalVotes;

    modifier onlyAdmin() { require(msg.sender == admin, "Not admin"); _; }

    function vote(Code c) external {
        require(votingOpen, "Voting closed");
        require(!hasVoted[msg.sender], "Already voted");
        hasVoted[msg.sender] = true;
        votes[c] += 1;
        totalVotes += 1;
    }

    function closeVoting() external onlyAdmin {
        votingOpen = false;
    }

    function leader() external view returns (Code best, uint count) {
        for (uint i = 0; i <= uint(type(Code).max); i++) {
            if (votes[Code(i)] > count) {
                count = votes[Code(i)];
                best = Code(i);
            }
        }
    }
}

Key Takeaways

Video : Project 1 : Smart Contract for Election System

Resource Files

• CandidateMaster.sol File
• VotePanelContract.sol File

Question / Answer (15 questions)

MCQ Test : Check Your Understanding (5 questions)

Select an option and press Check Answer, or answer all questions and press Submit Test to see your score. Each answer comes with an explanation.

Bibliography/References

The notes, questions and MCQs on this page are original explanations written for this course. The works listed below were consulted and are cited for attribution and further reading. Product names, logos and trademarks belong to their respective owners. Short quotations, where used, are marked and attributed.

1. Solidity Team. (n.d.). Types (value types, reference types, mappings, operators, conversions). Solidity Documentation. https://docs.soliditylang.org/en/latest/types.html
2. Solidity Team. (n.d.). Contracts (creating contracts, visibility and getters, function modifiers, constant and immutable, functions, events, custom errors, inheritance, abstract contracts, interfaces, libraries). Solidity Documentation. https://docs.soliditylang.org/en/latest/contracts.html
3. Solidity Team. (n.d.). Security Considerations. Solidity Documentation. https://docs.soliditylang.org/en/latest/security-considerations.html
4. Remix Project. (n.d.). Remix IDE Documentation. https://remix-ide.readthedocs.io/en/latest/
5. ethereum.org. (n.d.). Smart contract security. Ethereum Developer Documentation. https://ethereum.org/en/developers/docs/smart-contracts/security/
6. Modi, R. (2018). Solidity Programming Essentials: A beginner’s guide to build smart contracts for Ethereum and blockchain. Packt Publishing. ISBN 978-1-78883-138-3.