Solidity Fundamentals

Solidity is the most widely used programming language for writing smart contracts on Ethereum and EVM-compatible blockchains. It is a statically typed, object-oriented language influenced by JavaScript, Python, and C++.

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Setting Up a Solidity Development Environment

Tool	Purpose
Remix IDE	Browser-based IDE for quick prototyping (remix.ethereum.org)
Hardhat	JavaScript/TypeScript development framework for testing and deployment
Foundry	Rust-based toolkit with fast compilation and testing (forge, cast, anvil)
OpenZeppelin	Library of audited, reusable smart contract components
Slither	Static analysis tool for finding vulnerabilities

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Basic Contract Structure

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract SimpleStorage {
    // State variable (stored on-chain)
    uint256 private storedValue;

    // Event emitted when value changes
    event ValueChanged(uint256 newValue);

    // Function to set the value
    function set(uint256 _value) public {
        storedValue = _value;
        emit ValueChanged(_value);
    }

    // Function to get the value (view = no state modification)
    function get() public view returns (uint256) {
        return storedValue;
    }
}

Key Elements

Element	Description
pragma	Specifies the compiler version
contract	Similar to a class in other languages
State variables	Stored permanently on the blockchain
Functions	Executable units of code
Events	Log entries that external applications can listen to

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Data Types

Value Types

Type	Description	Example
bool	Boolean (true/false)	bool isActive = true;
uint256	Unsigned 256-bit integer	uint256 balance = 1000;
int256	Signed 256-bit integer	int256 temperature = -10;
address	20-byte Ethereum address	address owner = msg.sender;
bytes32	Fixed-size byte array	bytes32 hash = keccak256("data");
enum	User-defined enumeration	enum Status { Active, Paused }

Reference Types

Type	Description	Example
string	Dynamic-size UTF-8 string	string name = "Token";
bytes	Dynamic-size byte array	bytes data = hex"0123";
array	Fixed or dynamic size	uint256[] values;
mapping	Key-value store	mapping(address => uint256) balances;
struct	Custom data structure	struct User { string name; uint age; }

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Visibility and Access Control

Visibility	Description
public	Accessible from anywhere (external, internal, derived contracts)
private	Only accessible within the contract that defines it
internal	Accessible within the contract and derived contracts
external	Only callable from outside the contract (not internally without this)

Function Modifiers