Smart Contracts

Definition

A smart contract is a program stored on a blockchain that automatically executes when predetermined conditions are met. It encodes the rules of an agreement and enforces them programmatically — no intermediary (bank, lawyer, notary) is needed.

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Core Ideas

Properties

• Deterministic — given the same inputs and state, always produces the same output
• Immutable — once deployed, code cannot be changed (upgradeable patterns exist as workarounds)
• Transparent — code is publicly visible on-chain
• Trustless — execution is enforced by the network, not a central party
• Permissionless — anyone can deploy or interact with a contract

Ethereum & Solidity

Ethereum is the primary platform for smart contract development in the source notes.

Solidity basics:

pragma solidity ^0.8.0;
 
contract SimpleStorage {
    uint256 private value;
 
    function set(uint256 _value) public {
        value = _value;
    }
 
    function get() public view returns (uint256) {
        return value;
    }
}

Key concepts:

• address type for Ethereum accounts and contracts
• mapping for key-value storage
• event for emitting logs (cheaper than storage)
• modifier for access control
• payable for receiving ETH

Token Standards

Standard	Type	Use Case
ERC-20	Fungible token	Cryptocurrencies, governance tokens
ERC-721	Non-fungible (NFT)	Digital art, collectibles, ownership
ERC-1155	Multi-token	Games (items that are both fungible and non-fungible)

Security

Critical vulnerabilities in source notes:

• Re-entrancy — attacker re-enters the contract before balance update; fix with checks-effects-interactions pattern or ReentrancyGuard
• Integer overflow/underflow — use Solidity 0.8+ (built-in checks) or SafeMath
• Access control — use OpenZeppelin Ownable or role-based access
• Front-running — MEV (Miner Extractable Value) and commit-reveal schemes

Development Tooling

• Hardhat — local development environment, testing, deployment
• Truffle — older alternative; Ganache for local chain
• OpenZeppelin — audited contract library (tokens, access, governance)
• Etherscan — block explorer; contract verification

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Relationships

• Blockchain & Web3 — broader Web3 ecosystem
• Entrepreneurship & SaaS — DeFi protocols and Web3 product opportunities

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References

• Solidity development tutorials and notes