Why events communicate contract activity in Blockchain / Solidity - See It in Action

Why Events Communicate Contract Activity

📖 Scenario: Imagine you have a smart contract on the blockchain that tracks simple transactions. You want to know when someone sends money or performs an action without constantly checking the contract's state. Events help by sending messages that something happened.

🎯 Goal: You will create a simple Solidity contract that uses an event to announce when a user sends money. This shows how events communicate contract activity clearly and efficiently.

📋 What You'll Learn

Create a Solidity contract named SimpleBank

Declare an event named DepositMade with parameters address account and uint amount

Create a deposit function that accepts Ether and emits the DepositMade event

Add a public mapping balances to track user balances

Emit the event inside the deposit function after updating the balance

💡 Why This Matters

🌍 Real World

Events are used in blockchain apps to notify wallets, user interfaces, and other contracts about changes without expensive data reads.

💼 Career

Understanding events is essential for blockchain developers to build interactive and efficient decentralized applications.

1

Create the contract and balances mapping

Write a Solidity contract named SimpleBank and inside it declare a public mapping called balances that maps address to uint.

Blockchain / Solidity

contract SimpleBank {
    // Your code here
}

Need a hint?

Start by writing contract SimpleBank { } and inside it add mapping(address => uint) public balances;

2

Declare the DepositMade event

Inside the SimpleBank contract, declare an event named DepositMade that has two parameters: address account and uint amount.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleBank {
    mapping(address => uint) public balances;
    // Your code here
}

Need a hint?

Use the keyword event followed by the event name and parameters inside parentheses.

3

Create the deposit function and emit the event

Add a public payable function named deposit inside SimpleBank. Inside it, increase the sender's balance in balances by msg.value and then emit the DepositMade event with msg.sender and msg.value.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleBank {
    mapping(address => uint) public balances;
    event DepositMade(address account, uint amount);

    // Your code here
}

Need a hint?

Remember to mark the function as payable to accept Ether. Use emit to send the event.

4

Test the contract by calling deposit and observe event

Write a comment line that explains that when deposit is called, the DepositMade event will notify listeners about the deposit.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleBank {
    mapping(address => uint) public balances;
    event DepositMade(address account, uint amount);

    function deposit() public payable {
        balances[msg.sender] += msg.value;
        emit DepositMade(msg.sender, msg.value);
    }
}

// Your explanation here

Need a hint?

Write a comment starting with // explaining the event's purpose.