Example of a simple smart contract

A smart contract is a self-executing agreement written in code, deployed on blockchain platforms like Ethereum to automate actions when conditions are met.

Jul 16, 2025 at 11:50 pm

Understanding Smart Contracts

A smart contract is a self-executing contract with the terms of the agreement directly written into code. It runs on blockchain technology and automatically executes actions when predefined conditions are met. The most popular platform for deploying smart contracts is Ethereum, which uses the Solidity programming language.

To understand how a simple smart contract works, consider a basic example: a contract that stores a value and allows it to be updated. This can be used as a foundation for more complex applications such as token transfers, decentralized finance (DeFi) protocols, or NFTs.

Smart contracts eliminate intermediaries by enforcing trust through code, ensuring transparency and reducing the need for manual oversight.

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Writing a Basic Smart Contract in Solidity

Let’s create a simple smart contract using Solidity, Ethereum's primary programming language. This contract will store an unsigned integer and allow anyone to update its value.

Here’s the basic structure:

pragma solidity ^0.8.0;
contract SimpleStorage {
uint storedData;

function set(uint x) public {
    storedData = x;
}

function get() public view returns (uint) {
    return storedData;
}
}

This contract has two functions:

• set(uint x) – updates the stored value.
• get() – retrieves the current value.

Each line of this code plays a crucial role in defining the behavior of the contract on the Ethereum Virtual Machine (EVM).

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Deploying the Smart Contract

To deploy this contract, you’ll need:

• A Solidity compiler (e.g., Remix IDE)
• An Ethereum wallet (e.g., MetaMask)
• Testnet ETH for gas fees

Steps:

• Open Remix IDE
• Create a new file named SimpleStorage.sol
• Paste the above code into the editor
• Select the appropriate compiler version under the Compiler tab
• Switch to the Deploy & Run Transactions tab
• Choose Injected Web3 and connect your MetaMask wallet
• Click Deploy

Once deployed, you’ll see the contract address and available functions in the interface.

Deployment costs gas fees, so ensure your wallet contains sufficient testnet ETH before proceeding.

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Interacting with the Deployed Contract

After deployment, you can interact with the contract using the functions provided in Remix. These include setting and retrieving values.

To update the stored value:

• Expand the set function
• Enter a number in the input field
• Click transact
• Confirm the transaction in MetaMask

To retrieve the value:

• Expand the get function
• Click call

These interactions demonstrate how users can engage with blockchain-based applications without needing backend servers.

Every interaction with a smart contract requires a transaction, which must be signed and confirmed via your wallet.

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Security Considerations for Smart Contracts

Even a simple smart contract like this one should be reviewed for security best practices. While this example doesn’t involve sensitive data or funds, real-world contracts often do. Common issues include:

• Reentrancy attacks
• Integer overflow/underflow
• Improper access control

For this contract, adding modifiers to restrict who can call set could enhance security. For instance:

address owner;
constructor() {
owner = msg.sender;
}
modifier onlyOwner {
require(msg.sender == owner, "Only owner can call this function");
_;
}

Apply the modifier to the set function:

function set(uint x) public onlyOwner {
storedData = x;
}

Security should never be an afterthought in smart contract development, even for seemingly harmless contracts.

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Frequently Asked Questions

What tools are required to write and deploy a smart contract?

You can use online platforms like Remix IDE to write and deploy smart contracts without installing any software. Additionally, you'll need a wallet like MetaMask and some testnet ETH for gas fees.

Can I modify a deployed smart contract?

No, once a smart contract is deployed on the blockchain, its code cannot be changed. You would need to deploy a new contract if modifications are necessary.

How much does it cost to deploy a smart contract?

The cost depends on the complexity of the contract and the current network congestion. Simpler contracts cost less in gas fees compared to more complex ones.

Is it possible to read data from a smart contract without paying gas?

Yes, reading data via a view function does not alter the state and therefore does not require gas. However, writing or changing data always incurs a fee.