Mappings in Blockchain / Solidity - Mini Project: Build & Apply

Understanding Mappings in Solidity

📖 Scenario: You are creating a simple blockchain contract to store and retrieve user balances. This contract uses a mapping to link each user's address to their balance.

🎯 Goal: Build a Solidity contract that uses a mapping to store balances for addresses, set a balance for one user, and then retrieve and display that balance.

📋 What You'll Learn

Create a mapping named balances that links address to uint

Create a uint variable named initialBalance and set it to 100

Write a function setBalance that sets the initialBalance for the sender's address in balances

Write a function getBalance that returns the balance of the sender's address

Print the balance of the sender after setting it

💡 Why This Matters

🌍 Real World

Mappings are used in blockchain contracts to store data linked to user addresses, like balances, permissions, or votes.

💼 Career

Understanding mappings is essential for blockchain developers to manage user data efficiently and securely in smart contracts.

1

Create the mapping to store balances

Create a mapping named balances that links address to uint inside a contract named BalanceTracker.

Blockchain / Solidity

contract BalanceTracker {
    // Your code here
}

Need a hint?

Think of mapping as a dictionary where each address has a number (uint) balance.

2

Add an initial balance variable

Inside the BalanceTracker contract, create a uint variable named initialBalance and set it to 100.

Blockchain / Solidity

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

Need a hint?

This variable will hold the starting balance for users.

3

Write a function to set the sender's balance

Add a public function named setBalance inside BalanceTracker that sets the sender's balance in balances to initialBalance.

Blockchain / Solidity

contract BalanceTracker {
    mapping(address => uint) public balances;
    uint initialBalance = 100;

    // Your code here
}

Need a hint?

Use msg.sender to get the address calling the function.

4

Write a function to get the sender's balance and print it

Add a public view function named getBalance inside BalanceTracker that returns the sender's balance from balances. Then, write a comment showing how to call setBalance and getBalance to print the balance.

Blockchain / Solidity

contract BalanceTracker {
    mapping(address => uint) public balances;
    uint initialBalance = 100;

    function setBalance() public {
        balances[msg.sender] = initialBalance;
    }

    // Your code here
}

Need a hint?

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