First Solidity Program

Writing your first Solidity program is a great way to get familiar with the syntax, structure, and workflow of smart contracts on Ethereum. We’ll create a simple contract that stores and retrieves a message.

1. Understanding the Contract

A Solidity contract is similar to a class in object-oriented programming. It contains state variables, functions, and visibility modifiers.

In this example, we will create a contract called HelloWorld that:

• Stores a string message.
• Allows reading and updating the message.

2. The Code

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

contract HelloWorld {
    // State variable to store the message
    string public message;

    // Constructor to initialize the message when deploying the contract
    constructor(string memory initMessage) {
        message = initMessage;
    }

    // Function to update the message
    function setMessage(string memory newMessage) public {
        message = newMessage;
    }

    // Function to read the current message
    function getMessage() public view returns (string memory) {
        return message;
    }
}

3. Code Explanation

• pragma solidity ^0.8.20;
  Specifies the Solidity compiler version. The ^ symbol ensures compatibility with versions 0.8.20 and above.
• contract HelloWorld { ... }
  Defines a smart contract named HelloWorld.
• State Variable:
  string public message;
  This variable stores the message and is publicly readable.
• Constructor:
  constructor(string memory initMessage) initializes the message when the contract is deployed.
• setMessage Function:
  Updates the stored message. Marked as public so anyone can call it.
• getMessage Function:
  Returns the current message. view means it doesn’t change blockchain state and doesn’t cost gas when called externally.

4. Deploying on Remix IDE

1. Open Remix IDE.
2. Create a new file named HelloWorld.sol.
3. Paste the code above into the editor.
4. Go to the Solidity Compiler tab and click Compile HelloWorld.sol.
5. Go to the Deploy & Run Transactions tab:
   • Select the HelloWorld contract.
   • Enter an initial message (e.g., "Hello, Ethereum!").
   • Click Deploy.
6. Interact with the contract:
   • Click getMessage to read the message.
   • Use setMessage to update it, then call getMessage again to see the change.

5. Key Takeaways

• Solidity contracts are structured with state variables, functions, and optional constructors.
• Public variables automatically generate a getter function.
• View functions read blockchain state without costing gas.
• Remix IDE allows you to compile, deploy, and test smart contracts quickly without setting up a local environment.