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MetaInvestor.
Mar 29, 2025
Expert Q&A

How to generate random Number between 1&2 without VRF?

So I was making a coinflip game which assigns head- 1 and tails -2 and when user places bet on polygon chain.... smart contract generates a random number between 1 and 2 and if the outcome is same...user gets double - (5 % as fee to the owner of contract) ! from a pool and if outcome is different then user loses all and the lost amount is deposited in the pool - (3% as fee to the owner) (to fund winners)... but any way to make genrate a random number? I have no funds at all so I can't afford chainlink VRF to generate. So is there any other secure way for this? plus I am pritty new to solidity so I made this code with help of chat gpt but I don't it works....can anyone help to make the code better? code-

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract CoinFlip {
    address public owner;
    uint256 public contractBalance;
    
    event BetPlaced(address indexed player, uint256 amount, bool choice);
    event BetResult(address indexed player, uint256 amount, bool won);
    
    constructor() {
        owner = msg.sender;
    }
    
    function placeBet(bool choice) external payable {
        require(msg.value > 0, "Bet amount must be greater than 0");
        
        bool outcome = (block.timestamp % 2 == 0); // Simple pseudo-random outcome
        if (outcome == choice) {
            uint256 winAmount = (msg.value * 2 * 95) / 100;
            require(address(this).balance >= winAmount, "Insufficient contract balance");
            payable(msg.sender).transfer(winAmount);
            emit BetResult(msg.sender, winAmount, true);
        } else {
            uint256 lostAmount = (msg.value * 97) / 100;
            contractBalance += lostAmount;
            emit BetResult(msg.sender, msg.value, false);
        }
        emit BetPlaced(msg.sender, msg.value, choice);
    }
    
    function depositFunds() external payable {
        require(msg.sender == owner, "Only owner can deposit funds");
        contractBalance += msg.value;
    }
    
    function withdrawFunds(uint256 amount) external {
        require(msg.sender == owner, "Only owner can withdraw funds");
        require(amount <= address(this).balance, "Insufficient contract balance");
        payable(owner).transfer(amount);
        contractBalance -= amount;
    }
}
  • Smart Contract
  • Solidity
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0x67fc...27ac.
Mar 31 2025, 13:26

"but any way to make genrate a random number?" - not really, most blockchains and EVM in particular are deterministic by design. Code that you've generated is using block's timestamp for randomness but it can be manipulated with enough effort.

Some services like chainlink are posting random stuff on blockchain for other contracts to use, basically acting like a 3rd party with some math guarantees. There are chainlink alternatives but they are using very similar approaches and much less popular. So, if you want a good source of randomness on-chain then chainlink is likely your best bet as of now. In case you 're just learning solidity without worrying about security you might try the approach with the timestamp like in the generated snippet.

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