Creating a Smart Contract in Ethereum: Step-by-Step Guide

This guide walks you through writing, testing, and deploying a smart contract on Ethereum (or testnets like Sepolia/Goerli). We’ll use Solidity, Remix IDE, and MetaMask.

1. Prerequisites

Before you start, ensure you have:

MetaMask installed (Download here)
Testnet ETH (Get free ETH from Sepolia Faucet)
Basic understanding of Solidity (Ethereum’s smart contract language)

2. Writing the Smart Contract

We’ll create a simple “Hello World” contract that stores and retrieves a message.

Solidity Code

solidity

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

contract HelloWorld {
    string private message;

    // Constructor: Set initial message
    constructor(string memory _initialMessage) {
        message = _initialMessage;
    }

    // Function to update the message
    function setMessage(string memory _newMessage) public {
        message = _newMessage;
    }

    // Function to read the message
    function getMessage() public view returns (string memory) {
        return message;
    }
}

Key Components

pragma solidity ^0.8.0 → Specifies Solidity version.
string private message → State variable (stored on blockchain).
constructor() → Runs once at deployment.
setMessage() → Updates the stored message (costs gas).
getMessage() → Reads the message (free, no gas).

3. Compiling & Deploying

Using Remix IDE (Browser-Based)

Go to Remix IDE
Create a new file (HelloWorld.sol) and paste the code.
Compile:
- Go to the Solidity Compiler tab.
- Select compiler version 0.8.0+.
- Click Compile.
Deploy:
- Go to the Deploy & Run Transactions tab.
- Select Injected Provider – MetaMask (connect wallet).
- Choose Sepolia/Goerli testnet.
- Enter an initial message (e.g., "Hello, Ethereum!") in the constructor field.
- Click Deploy (confirm in MetaMask).

4. Interacting with the Contract

Once deployed:

Call getMessage() → Returns the stored message (no gas).
Call setMessage("New Message") → Updates the message (costs gas).

5. Verifying on Etherscan

Copy the contract address from Remix.
Go to Etherscan (or Sepolia Etherscan).
Search for your contract address.
Click “Verify & Publish” to make the code public.

6. Advanced: Deploying with Hardhat

For larger projects, use Hardhat (local development):

bash

npm install --save-dev hardhat
npx hardhat init

Edit scripts/deploy.js:

javascript

async function main() {
  const HelloWorld = await ethers.getContractFactory("HelloWorld");
  const hello = await HelloWorld.deploy("Hello, Hardhat!");
  await hello.deployed();
  console.log("Contract deployed to:", hello.address);
}

Run: