Voting Smart Contract

Our smart contract will be consisting of three main functions, which are 

1. Member Adding function
2. Voting function
3. Getting highest voted member

Let's first add compiler version and create voting contract ,

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.6;
pragma experimental ABIEncoderV2;

contract Voting{
      ...
}

Now let's create variables or objects

string[] public members;
mapping(string => uint) public memberVote;
mapping(address => bool) public voted;   

here mapping voted will prevent an user from voting multiple times and members array will add members

Voting Functions

Now lets Create functions for each mentioned operations ,

1. addMember() function :

function addMember(string memory name) public {
        bool repeated=false;
        for(uint i=0; i < members.length; i++){
            if(keccak256(abi.encodePacked((name))) == keccak256(abi.encodePacked(members[i]))){
                repeated = true;
            }
        }
        if(repeated==false){
            members.push(name);
            memberVote[name] = 0;
        }
}

It will check if member already present in the members array , if not it will add it to members array

2.  Vote() function :

function Vote(string memory name) public{
        require(voted[msg.sender]==false, 'one address one vote');
        memberVote[name] = memberVote[name]+1;
        voted[msg.sender]=true;
}

voted mapping will let voters vote one time only , voter can vote with this function with input  as member's name 

3. highestVoted() :

function highestVoted() public view returns(string memory){
        uint maxIndex=0;
        uint maxVote=0;
        for(uint i = 0; i<members.length; i++){
            if(memberVote[members[i]]>maxVote){
                maxIndex=i;
                maxVote=memberVote[members[i]];
            }
        }
        return members[maxIndex];
}

this function will return member with highest votes 

So this is our basic voting smart contract and here is the full code for the same ,

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.6;
pragma experimental ABIEncoderV2;

contract Voting{

    string[] public members;
    mapping(string => uint) public memberVote;
    mapping(address => bool) public voted;

    function addMember(string memory name) public {
        bool repeated=false;
        for(uint i=0; i < members.length; i++){
            if(keccak256(abi.encodePacked((name))) == keccak256(abi.encodePacked(members[i]))){
                repeated = true;
            }
        }
        if(repeated==false){
            members.push(name);
            memberVote[name] = 0;
        }
    }

    function Vote(string memory name) public{
        require(voted[msg.sender]==false, 'one address one vote');
        memberVote[name] = memberVote[name]+1;
        voted[msg.sender]=true;
    }

    function highestVoted() public view returns(string memory){
        uint maxIndex=0;
        uint maxVote=0;
        for(uint i = 0; i<members.length; i++){
            if(memberVote[members[i]]>maxVote){
                maxIndex=i;
                maxVote=memberVote[members[i]];
            }
        }
        return members[maxIndex];
    }

    function getMembers() public view returns(string[] memory){
        return members;
    }
    function getVotes(string memory member) public view returns(uint){
        return memberVote[member];
    }

}