code

 //SPDX-License-Identifier: GPL-3.0

 pragma solidity >=0.5.0 <0.9.0;

 contract lottery{
      address public manager;
      address payable[] public participants;

      constructor()
      {
          manager=msg.sender;
          //hadi

      }

      receive() external payable{ //to recieve ether
          require(msg.value==1 ether);
          participants.push(payable(msg.sender));
      }
      function getBalance() public view returns(uint){
         require(msg.sender==manager);
          return address(this).balance;
      }
      function random() public view returns(uint){
      return uint(keccak256(abi.encodePacked(block.difficulty,block.timestamp,participants.length)));
  
                   
  }
  function selectWinner() public {
      require(msg.sender==manager);
      require(participants.length>=3);
      uint r=random();
      address payable winner;
      uint index = r % participants.length;
      winner=participants[index];
      winner.transfer(getBalance());          //eth will be transfered to the winner
      participants =new address payable[](0);  //dynamic array reset
       

  }


  }