I'm creating Ether Coin Flip. Works like this.

  • Person A calls new coin flip function with 1 Ether
  • Person B calls End coin flip function with 1 Ether
  • Smart contract uses VRF to randomly pick winner
  • Smart contract sends all Ether to winner

There are no parameters for the new coin flip function. How will the smart contract know to use that function?

Should I create an arbitrary parameter or what?

Here's the smart contract so far.

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

// Testing on Rinkeby network

import "@chainlink/contracts/src/v0.6/VRFConsumerBase.sol";

contract EtherCoinFlip is VRFConsumerBase {
    uint256 minimumEth = 100000;
    uint256 etherWinnings;

    struct EtherCoinFlipStruct {
        address payable betStarter;
        uint256 startingWager;
        address payable betEnder;
        uint256 endingWager;
        uint256 etherTotal;
        address payable winner;
        address payable loser;

    uint256 numCoinFlips = 300;
    mapping(uint256 => EtherCoinFlipStruct) EtherCoinFlipStructs;
    // VRF logic
    bytes32 private s_keyHash;
    uint256 private s_fee;
    uint256 public randomResult;
    constructor(address vrfCoordinator, address link, bytes32 keyHash, uint256 fee) 
        VRFConsumerBase(vrfCoordinator, link) public
        s_keyHash = keyHash;
        s_fee = fee;

     * Callback function used by VRF Coordinator
    function fulfillRandomness(bytes32 requestId, uint256 randomness) internal override {
        randomResult = randomness;
    // Emit the event
    event EtherCoinFlipped(uint256 indexed coinFlipID, bytes32 indexed requestId);
    // Start the Ether coin flip
    function newCoinFlip() public payable returns (uint256 coinFlipID, bytes32 requestId) {
        require(msg.value >= minimumEth);
        require(LINK.balanceOf(address(this)) >= s_fee, "Not enough LINK to pay fee");
        requestId = requestRandomness(s_keyHash, s_fee);
        coinFlipID = numCoinFlips++;
        EtherCoinFlipStructs[coinFlipID] = EtherCoinFlipStruct(
        emit EtherCoinFlipped(coinFlipID, requestId);
    event EtherCoinFinishedFlip(address indexed winner);
    // End the Ether coin flip
    function endCoinFlip(uint256 coinFlipID, uint256 randomness) public payable {
        // require(msg.value == startingWager);
        require(coinFlipID == coinFlipID);
        EtherCoinFlipStruct memory c = EtherCoinFlipStructs[coinFlipID];
        c.betEnder = msg.sender;
        c.endingWager = msg.value;
        c.etherTotal = c.startingWager + c.endingWager;
        // Return the randomness result & detirmine the winner
        uint256 finalVerdict = randomness;
        if ((finalVerdict % 2) == 0) {
            c.winner = c.betStarter;
        } else {
            c.winner = c.betEnder;

        emit EtherCoinFinishedFlip(c.winner);

You just need to specify amount to pay with require(amount >= PRICE, "Not enough ETH payed!"). To interact with contract and send ETH to it, it is JavaScript or Python or Java work with libraries.

You just have to set a function payable in solidity.

If I misunderstood, tell more about what exactly you want


There's absolutely no issue with calling a function that doesn't accept any parameters.

For example, in web3.js to call the function you would simply do this and the transaction would go through:

await contract.methods.newCoinFlip().send({
  from: userAddress,
  value: "1000000000000000000" // 1 ETH in wei

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