Why functions define contract behavior in Blockchain / Solidity - See It in Action

Why Functions Define Contract Behavior

📖 Scenario: Imagine you are creating a simple blockchain contract that manages a digital wallet. This wallet can receive and send tokens. To control how tokens move, you use functions. Each function defines a specific behavior of the contract, like depositing or withdrawing tokens.

🎯 Goal: Build a basic Solidity contract with functions that define how tokens are deposited and withdrawn. Learn how functions shape the contract's behavior.

📋 What You'll Learn

Create a Solidity contract named SimpleWallet

Add a state variable balance of type uint to store tokens

Write a function deposit that increases the balance by a given amount

Write a function withdraw that decreases the balance by a given amount if enough tokens exist

Print the balance after transactions

💡 Why This Matters

🌍 Real World

Blockchain contracts control digital assets and define rules for transactions. Functions are the building blocks that let users interact with these assets safely.

💼 Career

Understanding how functions define contract behavior is essential for blockchain developers creating secure and reliable smart contracts.

1

Create the contract and state variable

Write a Solidity contract named SimpleWallet and inside it declare a public uint variable called balance initialized to 0.

Blockchain / Solidity

contract SimpleWallet {
    // Declare public uint variable balance initialized to 0
    // Your code here
}

Need a hint?

Use contract SimpleWallet {} to start and inside declare uint public balance = 0;

2

Add the deposit function

Inside the SimpleWallet contract, write a public function named deposit that takes a uint parameter called amount and adds it to balance.

Blockchain / Solidity

contract SimpleWallet {
    uint public balance = 0;

    // Write public function deposit(uint amount) that adds amount to balance
    // Your code here
}

Need a hint?

Define function deposit(uint amount) public and inside add amount to balance.

3

Add the withdraw function with check

Inside the SimpleWallet contract, write a public function named withdraw that takes a uint parameter called amount. It should subtract amount from balance only if balance is greater than or equal to amount.

Blockchain / Solidity

contract SimpleWallet {
    uint public balance = 0;

    function deposit(uint amount) public {
        balance += amount;
    }

    // Write public function withdraw(uint amount) that subtracts amount from balance if balance >= amount
    // Your code here
}

Need a hint?

Use an if statement to check balance >= amount before subtracting.

4

Test the contract behavior

Add a public view function named getBalance that returns the current balance. Then, simulate calling deposit(100) and withdraw(40) and print the result of getBalance().

Blockchain / Solidity

contract SimpleWallet {
    uint public balance = 0;

    function deposit(uint amount) public {
        balance += amount;
    }

    function withdraw(uint amount) public {
        if (balance >= amount) {
            balance -= amount;
        }
    }

    // Add public view function getBalance() that returns balance
    // Your code here
}

// Simulate calls and print balance
// Your code here

Need a hint?

Define getBalance() to return balance. Simulate calls by comments or test framework.