Understanding Solidity's Data Types: A Beginner's Guide

🧱 Why Data Types Matter

Solidity is a statically-typed language, meaning you must declare variable types explicitly. This:

  • 🧠 Helps prevent errors
  • ⛽ Optimizes gas costs
  • 🔒 Enhances security

📦 Basic Value Types

1. Integers

int8 public temperature = -25;   // Signed (-128 to 127)
uint256 public balance = 1000;   // Unsigned (0 to 2²⁵⁶-1)
Type Range
int8/int16/.../int256 -2^(n-1) to 2^(n-1)-1
uint8/uint16/.../uint256 0 to 2^n-1

Best Practice: Use uint256 unless you need smaller sizes

2. Address Type

address public user = 0x742d35Cc6634C0532925a3b844Bc454e4438f44e;
address payable public recipient = payable(user);
  • Regular address: 20-byte Ethereum address
  • Payable address: Can receive ETH

🧩 Reference Types

1. Arrays

uint256[5] public fixedArray;           // Fixed size
uint256[] public dynamicArray;          // Dynamic size
string[] public names = ["Alice", "Bob"];

Memory Arrays

function createArray() pure public {
    uint256[] memory temp = new uint256[](3);
}

Storage Arrays

uint256[] public storedArray;

function addElement(uint256 value) public {
    storedArray.push(value);
}

2. Structs

struct User {
    address wallet;
    uint256 balance;
    bool isActive;
}

User public newUser = User(msg.sender, 100, true);

🔍 Special Types

1. Mappings

mapping(address => uint256) public balances;

function updateBalance(uint256 amount) public {
    balances[msg.sender] = amount;
}

Note: No iteration support - use with external libraries

2. Bytes & Strings

bytes32 public hash = keccak256(abi.encode("Hello"));
string public greeting = "Welcome!";
Type Best For
bytes1-bytes32 Fixed-size binary data
bytes Dynamic binary data
string UTF-8 text

💡 Pro Tips for Beginners

  1. Always initialize variables explicitly
  2. Use memory for temporary reference types
  3. Prefer bytes32 over string for fixed data
  4. Validate addresses with address(0) checks

🧪 Practice Challenge

Create a UserRegistry contract that:

  1. Stores user addresses in an array
  2. Tracks balances with a mapping
  3. Uses a struct to store user details
  4. Implements basic CRUD operations
// Starter code
contract UserRegistry {
    struct User {
        address wallet;
        uint256 balance;
        bool active;
    }
    
    // Add your implementation here
}

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