Basic Contract

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract SimpleStorage {
    uint256 private storedData;
    
    event ValueChanged(uint256 newValue);
    
    function set(uint256 x) public {
        storedData = x;
        emit ValueChanged(x);
    }
    
    function get() public view returns (uint256) {
        return storedData;
    }
}

Data Types

Function Modifiers

contract Owned {
    address public owner;
    
    constructor() {
        owner = msg.sender;
    }
    
    modifier onlyOwner() {
        require(msg.sender == owner, "Not owner");
        _;
    }
    
    function changeOwner(address newOwner) public onlyOwner {
        owner = newOwner;
    }
}

Common Patterns

• require(): Input validation and error handling
• payable: Functions that receive Ether
• msg.sender: Address calling the function
• msg.value: Amount of Ether sent
• address.transfer(): Send Ether safely
• Events: Log important state changes