Demystifying Solidity: A Step-by-Step Guide Using Walkthrough.sol

In this tutorial, we'll explore the structure and functionality of a simple Solidity smart contract named "Walkthrough". This walkthrough is designed for beginners to understand how smart contracts operate on the Ethereum blockchain.

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📜 The Walkthrough Contract — Full Source

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

contract Walkthrough {
    string public password;
    uint8 public infoNum = 42;
    string public theMethodName = "The method name is method7123949.";
    bool private cleared = false;

    // constructor
    constructor(string memory _password) {
        password = _password;
    }

    function info() public pure returns (string memory) {
        return "You will find what you need in info1().";
    }

    function info1() public pure returns (string memory) {
        return 'Try info2(), but with "hello" as a parameter.';
    }

    function info2(string memory param) public pure returns (string memory) {
        if (keccak256(abi.encodePacked(param)) == keccak256(abi.encodePacked("hello"))) {
            return "The property infoNum holds the number of the next info method to call.";
        }
        return "Wrong parameter.";
    }

    function info42() public pure returns (string memory) {
        return "theMethodName is the name of the next method.";
    }

    function method7123949() public pure returns (string memory) {
        return "If you know the password, submit it to authenticate().";
    }

    function authenticate(string memory passkey) public {
        if (keccak256(abi.encodePacked(passkey)) == keccak256(abi.encodePacked(password))) {
            cleared = true;
        }
    }

    function getCleared() public view returns (bool) {
        return cleared;
    }
}

Here’s the logical flow a user should follow when interacting with the contract:

1. Call info() → directs to info1()
2. Call info1() → suggests info2("hello")
3. Call info2("hello") → reveals infoNum
4. Call infoNum() → reveals 42
5. Call info42() → provides theMethodName
6. Call theMethodName() → provides method7123949
7. Call method7123949() → instructs to use authenticate()
8. Call authenticate(password) → sets cleared to true
9. Call getCleared() → confirms authentication

⏱️ Estimated time:

• 5 minutes to read
• 15–20 minutes if you follow along step-by-step in Remix

🛠️ How to Deploy This Contract Using Remix

• Go to Remix IDE

  • 👉 https://remix.ethereum.org

• Create a New File

  • In the left sidebar, click the “File explorer” icon, you can find "FILE EXPLORER" panel
  • Click the “Create new file” icon in the "FILE EXPLORER" panel to create a new file
  • Name it Walkthrough.sol
  • Paste the Contract into the main editor

• Compile the Contract

  • Click the “Solidity compiler” tab (third from top) on the left sidebar
  • Confirm that the compiler version matches (0.8.x)
  • Click the “Compile Walkthrough.sol” button

• Deploy the Contract

  • Click the ‘Deploy & Run Transactions’ tab (fourth icon: Ethereum logo) to open the ‘DEPLOY & RUN TRANSACTIONS’ panel
  • At the top of the 'DEPLOY & RUN TRANSACTIONS' panel, set the Environment to 'Remix VM (Cancun)'
  • Provide Constructor Argument such as "some_password" (including the quotes!), and click "Deploy" button
  • Alternatively, click the down arrow to reveal a field labeled string _password, and provide "some_password" (including the quotes!) and click "transact" button

• Run/Interact with the contract

  • Scroll down in the panel to see the deployed contract instance
  • Expand the Contract by clicking the little arrow beside the deployed contract to view its functions
  • Run the methods info(), info1(), info2("hello"), and so on.
  • If you run the method getCleared() and receive true, you’ve successfully completed the walkthrough.

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🔗 Reference

This walkthrough is based on a smart contract challenge from Ethernaut, a Web3 security game created by OpenZeppelin.

You can view the original level here:

👉 The ethernaut - Hello Ethernaut

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✍️ Written by Yuanyan Wu — software engineer learning smart contract security, one contract at a time. If you'd like to see more Solidity walkthroughs like this — or want a deeper dive into smart contract vulnerabilities — let me know in the comments.