Function declaration and syntax in Blockchain / Solidity - Mini Project: Build & Apply

Function Declaration and Syntax in Blockchain Smart Contracts

📖 Scenario: You are creating a simple blockchain smart contract to store and retrieve a favorite number. This contract will help you understand how to declare and use functions in Solidity, the language used for Ethereum smart contracts.

🎯 Goal: Build a smart contract with a function to set a favorite number and another function to get that number.

📋 What You'll Learn

Create a state variable to store a number

Declare a function called setFavoriteNumber that takes a number as input and stores it

Declare a function called getFavoriteNumber that returns the stored number

Use correct Solidity function syntax including visibility and return types

💡 Why This Matters

🌍 Real World

Smart contracts on blockchains store and manage data securely. Functions let users interact with this data.

💼 Career

Understanding function declaration and syntax is essential for blockchain developers writing smart contracts.

1

Create a state variable

Create a public state variable called favoriteNumber of type uint to store the number.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FavoriteNumber {
    // Declare a public uint variable named favoriteNumber
    
    // Your code here
}

Need a hint?

Use uint public favoriteNumber; inside the contract to create the variable.

2

Declare the setter function

Add a public function called setFavoriteNumber that takes a uint parameter named _number and sets favoriteNumber to this value.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FavoriteNumber {
    uint public favoriteNumber;

    // Declare setFavoriteNumber function here
    
    // Your code here
}

Need a hint?

Define the function with function setFavoriteNumber(uint _number) public and assign favoriteNumber = _number;.

3

Declare the getter function

Add a public view function called getFavoriteNumber that returns a uint and returns the value of favoriteNumber.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FavoriteNumber {
    uint public favoriteNumber;

    function setFavoriteNumber(uint _number) public {
        favoriteNumber = _number;
    }

    // Declare getFavoriteNumber function here
    
    // Your code here
}

Need a hint?

Use function getFavoriteNumber() public view returns (uint) and return the variable.

4

Test the contract output

Print the value returned by getFavoriteNumber() after setting it to 42 using setFavoriteNumber(42). Use comments to show the expected output.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FavoriteNumber {
    uint public favoriteNumber;

    function setFavoriteNumber(uint _number) public {
        favoriteNumber = _number;
    }

    function getFavoriteNumber() public view returns (uint) {
        return favoriteNumber;
    }
}

// Simulate setting and getting the favorite number
// Your code here

Need a hint?

In Solidity, you cannot print directly. Use comments to show calling setFavoriteNumber(42) then getFavoriteNumber() returns 42.