# Universal Router Exercises In this exercise, you'll learn how to use the [`UniversalRouter`](https://github.com/Uniswap/universal-router/blob/main/contracts/UniversalRouter.sol) contract. The starter code for this exercise is provided in [`foundry/src/exercises/UniversalRouter.sol`](https://github.com/Cyfrin/defi-uniswap-v4/blob/main/foundry/src/exercises/UniversalRouter.sol) Solution is in [`foundry/src/solutions/UniversalRouter.sol`](https://github.com/Cyfrin/defi-uniswap-v4/blob/main/foundry/src/solutions/UniversalRouter.sol) ## Task 1 - Swap ```solidity function swap( PoolKey calldata key, uint128 amountIn, uint128 amountOutMin, bool zeroForOne ) external payable { // Write your code here } ``` Call `UniversalRouter` to swap currencies on Uniswap V4 pool. - Transfer currency to swap from `msg.sender` into this contract. - Grant `Permit2` approvals to `UniversalRouter`. - Prepare the inputs to call `UniversalRouter.execute`. - The command to execute is `Commands.V4_SWAP`. - The input for this command encodes `actions` and `params`. - `actions` are `Actions.SWAP_EXACT_IN_SINGLE`, `Actions.SETTLE_ALL` and `Actions.TAKE_ALL`. - `params` are inputs corresponding to each action. See [`_handleAction`](https://github.com/Uniswap/v4-periphery/blob/60cd93803ac2b7fa65fd6cd351fd5fd4cc8c9db5/src/V4Router.sol#L32-L80) for the correct inputs. - Call `UniverswalRouter.execute` - Withdraw both currency 0 and 1 to `msg.sender`. ## Test ```shell forge test --fork-url $FORK_URL --match-path test/UniversalRouter.test.sol -vvv ```