Arrays (fixed and dynamic) in Blockchain / Solidity - Mini Project: Build & Apply

Working with Fixed and Dynamic Arrays in Solidity

📖 Scenario: You are building a simple smart contract to manage a list of favorite numbers. Some numbers are fixed and cannot be changed, while others can be added dynamically by users.

🎯 Goal: Create a Solidity contract that uses both fixed-size and dynamic arrays to store numbers. You will initialize a fixed array, set a limit for adding numbers dynamically, add numbers to the dynamic array, and finally display all stored numbers.

📋 What You'll Learn

Create a fixed-size array called fixedNumbers with exactly 3 numbers: 10, 20, and 30

Create a dynamic array called dynamicNumbers to store unsigned integers

Create a variable called maxDynamicNumbers set to 5 to limit additions to the dynamic array

Write a function addNumber(uint number) that adds a number to dynamicNumbers only if it has less than maxDynamicNumbers elements

Write a function getAllNumbers() that returns both arrays combined as a single array

💡 Why This Matters

🌍 Real World

Smart contracts often need to store fixed and changing lists of data, like token balances or user inputs.

💼 Career

Understanding arrays in Solidity is essential for blockchain developers building decentralized applications.

1

Create a fixed-size array with 3 numbers

Create a fixed-size array called fixedNumbers of type uint[3] and initialize it with the numbers 10, 20, and 30 inside the contract.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FavoriteNumbers {
    // Create fixed-size array fixedNumbers with 10, 20, 30
    // Your code here
}

Need a hint?

Use uint[3] fixedNumbers = [10, 20, 30]; inside the contract to create the fixed array.

2

Add a dynamic array and a max limit variable

Add a dynamic array called dynamicNumbers of type uint[] and a variable called maxDynamicNumbers set to 5 inside the contract.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FavoriteNumbers {
    uint[3] fixedNumbers = [10, 20, 30];
    // Add dynamic array dynamicNumbers and maxDynamicNumbers = 5
    // Your code here
}

Need a hint?

Use uint[] dynamicNumbers; for the dynamic array and uint maxDynamicNumbers = 5; for the limit.

3

Write a function to add numbers to the dynamic array with a limit

Write a public function called addNumber that takes a uint number as input. Inside the function, add the number to dynamicNumbers only if the length of dynamicNumbers is less than maxDynamicNumbers.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FavoriteNumbers {
    uint[3] fixedNumbers = [10, 20, 30];
    uint[] dynamicNumbers;
    uint maxDynamicNumbers = 5;

    // Write addNumber function to add number if dynamicNumbers length < maxDynamicNumbers
    // Your code here
}

Need a hint?

Use dynamicNumbers.length to check the size and dynamicNumbers.push(number); to add.

4

Create a function to return all numbers combined

Write a public view function called getAllNumbers that returns a uint[] memory array containing all numbers from fixedNumbers followed by all numbers from dynamicNumbers. Combine both arrays inside the function.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FavoriteNumbers {
    uint[3] fixedNumbers = [10, 20, 30];
    uint[] dynamicNumbers;
    uint maxDynamicNumbers = 5;

    function addNumber(uint number) public {
        if(dynamicNumbers.length < maxDynamicNumbers) {
            dynamicNumbers.push(number);
        }
    }

    // Write getAllNumbers function to return combined fixedNumbers and dynamicNumbers
    // Your code here
}

Need a hint?

Create a new array with size equal to the sum of both arrays, copy elements from each, then return it.