> For the complete documentation index, see [llms.txt](https://docs.arpanetwork.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.arpanetwork.io/randcast/using-the-sdk/consumer-contract-examples/example-draw-a-lottery.md).

# Example - Draw a Lottery

The `DrawLotteryExample` illustrates the utilization of `GeneralRandcastConsumerBase` and [`RandcastSDK`](/randcast/using-the-sdk/randcast-utilities.md) to construct a straightforward lottery system.

```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;

import {
    GeneralRandcastConsumerBase,
    BasicRandcastConsumerBase
} from "randcast-user-contract/user/GeneralRandcastConsumerBase.sol";
// solhint-disable-next-line no-global-import
import "randcast-user-contract/user/RandcastSDK.sol" as RandcastSDK;

contract DrawLotteryExample is GeneralRandcastConsumerBase {
    /* requestId -> randomness */
    mapping(bytes32 => uint256[]) public randomResults;
    uint256[] public winnerResults;
    uint32 public ticketNumber;
    uint32 public winnerNumber;

    // solhint-disable-next-line no-empty-blocks
    constructor(address adapter) BasicRandcastConsumerBase(adapter) {}
    event LotteryTicketGenerated(uint256[] ticketResults);
    /**
     * Requests randomness
     */
    function getTickets(uint32 ticketNum, uint32 winnerNum) external returns (bytes32) {
        ticketNumber = ticketNum;
        winnerNumber = winnerNum;
        bytes memory params = abi.encode(ticketNumber);
        return _requestRandomness(RequestType.RandomWords, params);
    }

    /**
     * Callback function used by Randcast Adapter
     */
    function _fulfillRandomWords(bytes32 requestId, uint256[] memory randomWords) internal override {
        randomResults[requestId] = randomWords;
        emit LotteryTicketGenerated(randomWords);
        winnerResults = RandcastSDK.draw(randomWords[randomWords.length - 1], randomWords, winnerNumber);
    }

    function lengthOfWinnerResults() public view returns (uint256) {
        return winnerResults.length;
    }

    function getTicketResults(bytes32 requestId) public view returns (uint256[] memory) {
        return randomResults[requestId];
    }
}

```

The contract structure is similar to the previous example:

It first issues a random number request, setting the request type to`RequestType.RandomWord`, and sets `params` for the length of the returned array (the total number of lottery tickets). Upon receiving the tickets in the form of an array, in the `_fulfillRandomWords` function, we call the `RandcastSDK.draw` method to randomly pick a subset of elements based on their index positions in the array representing the winners.

If you want to draw a subset of elements from an existing array, consider requesting a single randomness by using `_requestRandomness(RequestType.Randomness, params)` and then calling `draw(randomness, indices, winnerNumber)`.


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