## Introduction to Curve.fi on Ethereum In this lesson, we'll learn how to swap DAI for USDC on Curve.fi. ### The Swap Function We will call the `exchange()` function in the `IStableSwap3Pool` interface to perform the swap. ### The `exchange()` function The `exchange()` function takes in the following parameters: * `i`: The index for the token in. * `j`: The index for the token out. * `dx`: The amount of token in that you're going to put in. * `min_dy`: The minimum amount of token out that you expect to get back. ### Let's get started To call the `exchange()` function to swap DAI for USDC, we can navigate to the `IStableSwap3Pool.sol` file under the "interfaces/curve" directory. ```bash cd interfaces/curve ``` The file contains the `exchange()` function that we will use. ```javascript function exchange(int128 i, int128 j, uint256 dx, uint256 min_dy) external; ``` The `exchange()` function is part of the `IStableSwap3Pool` interface. The `IStableSwap3Pool` interface is defined in the `IStableSwap3Pool.sol` file. We can import the `IStableSwap3Pool` interface into our test file so that we can use the `exchange()` function. ```javascript import "./src/interfaces/curve/IStableSwap3Pool.sol"; ``` We will import the `DAI`, `USDC`, and `USDT` constants from the `constants.sol` file. ```javascript import (DAI, USDC, USDT, CURVE_3POOL) from "./src/constants.sol"; ``` We can call the `exchange()` function from our test file to perform a swap. ```javascript pool.exchange(DAI, USDC, dx, min_dy); ``` We will cover calling the `exchange()` function in a later lesson.