State variables in Blockchain / Solidity - Mini Project: Build & Apply

Understanding State Variables in Solidity

📖 Scenario: You are creating a simple smart contract on the Ethereum blockchain to store and retrieve a number. This number should be saved permanently on the blockchain so that anyone can see it later.

🎯 Goal: Build a Solidity smart contract that uses a state variable to store a number and a function to read that number.

📋 What You'll Learn

Create a uint state variable named storedNumber.

Write a function named setNumber that takes a uint input and updates storedNumber.

Write a function named getNumber that returns the current value of storedNumber.

💡 Why This Matters

🌍 Real World

Smart contracts use state variables to keep track of balances, ownership, and other important data that must persist on the blockchain.

💼 Career

Understanding state variables is essential for blockchain developers to create secure and functional decentralized applications.

1

Create the state variable

Create a Solidity contract named SimpleStorage. Inside it, declare a uint state variable called storedNumber.

Blockchain / Solidity

contract SimpleStorage {
    // Declare the state variable storedNumber here
    
}

Need a hint?

State variables are declared inside the contract but outside any function.

2

Add a function to set the number

Inside the SimpleStorage contract, write a public function named setNumber that takes a uint parameter named num and assigns it to the state variable storedNumber.

Blockchain / Solidity

contract SimpleStorage {
    uint storedNumber;

    // Write the setNumber function here
}

Need a hint?

The function should be public so anyone can call it to update the number.

3

Add a function to get the number

Inside the SimpleStorage contract, write a public view function named getNumber that returns the current value of the storedNumber state variable.

Blockchain / Solidity

contract SimpleStorage {
    uint storedNumber;

    function setNumber(uint num) public {
        storedNumber = num;
    }

    // Write the getNumber function here
}

Need a hint?

The view keyword means the function does not change the state.

4

Test the contract output

Write a comment showing the expected output when setNumber(42) is called and then getNumber() is called.

Blockchain / Solidity

contract SimpleStorage {
    uint storedNumber;

    function setNumber(uint num) public {
        storedNumber = num;
    }

    function getNumber() public view returns (uint) {
        return storedNumber;
    }
}

// Your expected output comment here

Need a hint?

The comment should clearly show the stored number after setting it.