Hello World in Solidity

The simplest possible Solidity smart contract that demonstrates basic structure and a simple function.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
 
contract HelloWorld {
    // State variable to store the greeting
    string private greeting = "Hello World!";
    
    // Event emitted when greeting is changed
    event GreetingChanged(string newGreeting);
    
    // Returns the current greeting
    function getGreeting() public view returns (string memory) {
        return greeting;
    }
    
    // Changes the greeting
    function setGreeting(string memory _newGreeting) public {
        greeting = _newGreeting;
        emit GreetingChanged(_newGreeting);
    }
}

What’s happening here?

1. First line specifies the license (required for all Solidity files)
2. pragma solidity ^0.8.0 indicates which Solidity version to use
3. contract HelloWorld defines a new contract named HelloWorld
4. We store a greeting in a private state variable
5. An event is defined to track greeting changes
6. Two functions are provided:
   • getGreeting() to read the current greeting
   • setGreeting() to change the greeting

This simple example demonstrates:

• State variables
• Functions (both view and state-changing)
• Events
• Basic string handling
• Public/private visibility

Try it yourself in the Remix IDE: Open in Remix