Variables & Data Types

Solidity has three types of variables: state variables (stored on blockchain, cost gas to modify), local variables (exist only during function execution), and global variables (provide blockchain info like msg.sender, block.timestamp). Basic types include: uint (unsigned integers of various sizes), int (signed integers), address (20-byte Ethereum address), bool, string, and bytes. The default uint is uint256. Address types have special members like .balance and .transfer().