A collection of practice smart contract using the Solidity programming language

simpletransfer.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.9;

import "@openzeppelin/contracts/utils/math/SafeMath.sol";

contract TranferTokens {
    using SafeMath for uint;

    address public owner;

    // map user address to balance
    mapping(address => uint) public balances;

    modifier onlyOwner() {
        require(msg.sender == owner, "You are not the owner.");
        _;
    }


    // Constructor
    constructor() {
        owner = msg.sender;
    }

    // Fallback functions
    receive() external payable {} 

    fallback() external payable {} 

    function getCustomerBalance() external view returns (uint) {
        // return the balance of the caller
        return balances[msg.sender];
    }

    function transferToken(
        address to,
        uint transferAmount
    ) external payable returns (bool) {
        // check balance
        require(balances[msg.sender] >= transferAmount, "insufficient balance");

        // prevent underflow
        balances[msg.sender] = balances[msg.sender].sub(transferAmount);

        // transfer token 
        (bool success, ) = to.call{value: transferAmount}("");
        require(success, "Call failed");

        // update receiver's balance
        balances[to] = balances[to].add(transferAmount);

        return true;
    }
}

vote.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.9;

contract VotingSystem {
    // Option to be voted on
    string public option;
    
    // Mapping of voter addresses to their vote status
    mapping(address => bool) public voters;
    
    // Number of votes for each option
    uint256 public voteCount;
    
    // Event to be emitted when a new vote is cast
    event VoteCast(address voter);
    
    // Constructor function to set the option to be voted on
    constructor(string memory _option) {
        option = _option;
    }
    
    // Function to cast a vote for the given option
    function castVote() public {
        // Ensure voter has not already voted
        require(!voters[msg.sender], "You have already voted");
        
        // Mark voter as having voted
        voters[msg.sender] = true;
        
        // Increment vote count for option
        voteCount++;
        
        // Emit VoteCast event
        emit VoteCast(msg.sender);
    }
}