Flash loans in Blockchain / Solidity - Mini Project: Build & Apply

Flash Loans Basics

📖 Scenario: You are learning how flash loans work in blockchain smart contracts. Flash loans let you borrow tokens without collateral, but you must pay back the loan in the same transaction.We will create a simple smart contract that requests a flash loan, uses it, and repays it immediately.

🎯 Goal: Build a basic smart contract that requests a flash loan from a lending pool, performs a simple action, and repays the loan in the same transaction.

📋 What You'll Learn

Create a smart contract with a function to request a flash loan

Set up a variable to store the flash loan amount

Implement the callback function that executes after receiving the loan

Print/log the success message after repaying the loan

💡 Why This Matters

🌍 Real World

Flash loans are used in decentralized finance (DeFi) to perform arbitrage, refinancing, or collateral swaps without upfront capital.

💼 Career

Understanding flash loans is important for blockchain developers working on DeFi protocols, smart contract security, and financial applications.

1

Create the flash loan contract and amount variable

Create a smart contract named FlashLoanExample and declare a public variable loanAmount of type uint256 set to 1000 ether.

Blockchain / Solidity

contract FlashLoanExample {
    // Your code here
}

Need a hint?

Use contract FlashLoanExample {} to create the contract and declare uint256 public loanAmount = 1000 ether; inside it.

2

Add the flash loan request function

Inside the FlashLoanExample contract, add a public function requestFlashLoan() that will be used to start the flash loan process. For now, just add the function signature and an empty body.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FlashLoanExample {
    uint256 public loanAmount = 1000 ether;

    // Add the requestFlashLoan function below
    function requestFlashLoan() public {
        // Your code here
    }
}

Need a hint?

Define function requestFlashLoan() public {} inside the contract.

3

Implement the flash loan callback function

Add a function executeOperation() inside FlashLoanExample that takes parameters uint256 amount, uint256 fee, and returns bool. Inside it, write code to simulate using the loan and then returning true.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FlashLoanExample {
    uint256 public loanAmount = 1000 ether;

    function requestFlashLoan() public {
        // Flash loan request logic will go here
    }

    // Add executeOperation function below
    function executeOperation(uint256 amount, uint256 fee) public returns (bool) {
        // Your code here
    }
}

Need a hint?

Define executeOperation with the correct parameters and return true inside.

4

Print success message after loan repayment

Add a public function printSuccess() that prints the message "Flash loan repaid successfully!" using emit and an event named Success. Declare the event Success(string message) at the top of the contract. Then call printSuccess() at the end of executeOperation().

Blockchain / Solidity

pragma solidity ^0.8.0;

contract FlashLoanExample {
    uint256 public loanAmount = 1000 ether;

    // Declare Success event here

    function requestFlashLoan() public {
        // Flash loan request logic will go here
    }

    function executeOperation(uint256 amount, uint256 fee) public returns (bool) {
        // Simulate using the loan

        // Call printSuccess here

        // Return true to indicate success
        return true;
    }

    // Add printSuccess function here
}

Need a hint?

Declare event Success(string message); at the top. Use emit Success("Flash loan repaid successfully!"); inside printSuccess(). Call printSuccess() inside executeOperation().