Tutorial

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;


contract Example {


    // This is the owner of the contract
    address owner;


    // This is our counter struct. It will hold necessary information about the counter which are
    // number and description
    struct Counter {
        uint number;
        string description;
    }


    // Here we create an instance of our Counter.
    // It is empty for now, but we will initialize it in the constructor.
    Counter counter;


    // We will use this modidifer with our execute functions.
    // This modifiers make sure that the caller of the function is the owner of the contract.
    modifier onlyOwner() {
        require(msg.sender == owner, "Only the owner can increment or decrement the counter");
        _;
    }


    // This is our constructor function. It only runs once when we deploy the contract.
    // Since it takes two parameters, initial_value and description, they should be provided
    // when we deploy our contract.
    constructor(uint initial_value, string memory description) {
        owner = msg.sender;
        counter = Counter(initial_value, description);
      
    }


    // Below, we have two execute functions, increment_counter and decrement_counter
    // Since they modify data on chain, they require gas fee.
    // They are external functions, meaning they can only be called outside of the contract.
    // They also have the onlyOwner modifier which we created above. This make sure that
    // only the owner of this contract can call these functions.


    // This function gets the number field from the counter struct and increases it by one.
    function increment_counter() external onlyOwner {
        counter.number += 1;
        counter.description = " Increased by 1";
    }


    // This function is similar the one above, but instead of increasing we deacrease the number by one.
    function decrement_counter() external onlyOwner {
        counter.number -= 1;
       counter.description = "Decreased by 1";
    }


    // The function below is a query function.
    // It does not change any data on the chain. It just rerieves data.
    // We use the keyword view to indicate it retrieves data but does not change any.
    // Since we are not modifying any data, we do not pay any gas fee.


    // This function returns the number field of our counter struct.
    // Returning the current state of our counter.
    function get_counter_value() external view returns(uint) {
        return counter.number;
    }

    // This function returns the description of the counter
    function get_counter_description() external view returns(string memory)
        {return counter.description;
        }
    
    

    
}