Blockchain technology has revolutionized the financial world, enabling decentralized applications (dApps) and smart contracts. This guide will walk you through developing smart contracts and creating a cryptocurrency wallet with full source code, explanations, key points, and best practices.

1. Developing Smart Contracts

A smart contract is a self-executing program stored on a blockchain that runs when predefined conditions are met.

Prerequisites

• Basic knowledge of Solidity (Ethereum’s smart contract language).
• Node.js and npm installed.
• Hardhat or Truffle for smart contract development.
• A crypto wallet like MetaMask for testing.
• Ganache (for local blockchain testing) or Remix IDE (web-based).

Step 1: Setting Up the Development Environment

1. Install Node.js and npm:

   node -v
   npm -v
   

   If not installed, download from Node.js official site.

2. Install Hardhat:

   npm install --save-dev hardhat
   

   Initialize a project:

   npx hardhat
   

Step 2: Writing a Smart Contract

Create a Solidity file SimpleToken.sol inside the contracts directory.

SimpleToken.sol (Basic ERC-20 Token)

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

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract SimpleToken is ERC20 {
    constructor(uint256 initialSupply) ERC20("SimpleToken", "STK") {
        _mint(msg.sender, initialSupply * (10 ** decimals()));
    }
}

Key Points

• @openzeppelin/contracts/token/ERC20/ERC20.sol provides a secure ERC-20 implementation.
• ERC20("SimpleToken", "STK") sets the token name and symbol.
• _mint(msg.sender, initialSupply * (10 ** decimals())) creates initial supply.

Step 3: Deploying the Smart Contract

1. Configure Hardhat (hardhat.config.js):

   require("@nomicfoundation/hardhat-toolbox");
   
   module.exports = {
       solidity: "0.8.0",
       networks: {
           hardhat: {},
           rinkeby: {
               url: "https://rinkeby.infura.io/v3/YOUR_INFURA_PROJECT_ID",
               accounts: ["YOUR_PRIVATE_KEY"]
           }
       }
   };
   

   Replace YOUR_INFURA_PROJECT_ID and YOUR_PRIVATE_KEY.

2. Create a deployment script (scripts/deploy.js):

   const hre = require("hardhat");
   
   async function main() {
       const Token = await hre.ethers.getContractFactory("SimpleToken");
       const token = await Token.deploy(1000000);
       await token.deployed();
       console.log("Token deployed to:", token.address);
   }
   
   main().catch((error) => {
       console.error(error);
       process.exit(1);
   });
   

3. Run the deployment:

   npx hardhat run scripts/deploy.js --network rinkeby
   

Key Points

• Infura API enables blockchain interactions.
• deploy() handles contract creation and deployment.
• Rinkeby testnet is used for testing before mainnet deployment.

2. Creating a Cryptocurrency Wallet

A cryptocurrency wallet allows users to send, receive, and manage digital assets.

Prerequisites

• React.js for frontend.
• ethers.js for Ethereum interactions.
• MetaMask for wallet integration.

Step 1: Setting Up the React Project

1. Install React:

   npx create-react-app crypto-wallet
   cd crypto-wallet
   

2. Install dependencies:

   npm install ethers web3 react-toastify
   

Step 2: Implementing Wallet Functions

Modify App.js:

import React, { useState } from "react";
import { ethers } from "ethers";

function App() {
    const [account, setAccount] = useState(null);
    const [balance, setBalance] = useState(null);

    const connectWallet = async () => {
        if (window.ethereum) {
            const provider = new ethers.providers.Web3Provider(window.ethereum);
            await window.ethereum.request({ method: "eth_requestAccounts" });
            const signer = provider.getSigner();
            const address = await signer.getAddress();
            const balance = await provider.getBalance(address);
            setAccount(address);
            setBalance(ethers.utils.formatEther(balance));
        } else {
            alert("MetaMask is required.");
        }
    };

    return (
        <div>
            <h1>Crypto Wallet</h1>
            <button onClick={connectWallet}>Connect Wallet</button>
            {account && (
                <div>
                    <p>Account: {account}</p>
                    <p>Balance: {balance} ETH</p>
                </div>
            )}
        </div>
    );
}

export default App;

Key Points

• window.ethereum.request({ method: "eth_requestAccounts" }) connects MetaMask.
• ethers.providers.Web3Provider fetches blockchain data.
• ethers.utils.formatEther(balance) converts Wei to Ether.

Step 3: Sending Transactions

Modify App.js:

const sendTransaction = async () => {
    if (!account) return alert("Connect your wallet first!");

    const provider = new ethers.providers.Web3Provider(window.ethereum);
    const signer = provider.getSigner();
    
    try {
        const tx = await signer.sendTransaction({
            to: "0xReceiverAddress", // Replace with recipient
            value: ethers.utils.parseEther("0.01") // Send 0.01 ETH
        });
        await tx.wait();
        alert(`Transaction successful: ${tx.hash}`);
    } catch (error) {
        alert("Transaction failed: " + error.message);
    }
};

Add a button:

<button onClick={sendTransaction}>Send 0.01 ETH</button>

Key Points

• signer.sendTransaction() sends ETH.
• tx.wait() confirms the transaction.
• Error handling ensures robustness.

Final Thoughts

Smart Contracts

✔ Secure and self-executing
✔ Used in DeFi, NFTs, DAOs
✔ Requires testing before deployment

Crypto Wallet

✔ Stores and transfers tokens
✔ Uses MetaMask & ethers.js
✔ Essential for dApp interactions

This guide gives you a solid foundation in smart contract development and wallet creation. Ready to explore DeFi, NFTs, or custom blockchain solutions?