_You can follow along with the video course from here._ ### Introduction In this lesson, we will learn how to track addresses that are funding the contract and the amounts they will send to it. ### Tracking Funders To track the addresses are sending money to the contract, we can create an array of addresses named `funders`: ```js address[] public funders; ``` Whenever someone sends money to the contract, we will add their address to the array with the `push` function: ```js funders.push(msg.sender); ``` The `msg.sender` global variable refers to the address that **initiates the transaction**. ### Mapping Users to Funds Sent We can also map each funder's address to the amount they have sent using **mappings**. Let's define a mapping in Solidity: ```js mapping(address => uint256) public addressToAmountFunded; ``` The `addressToAmountFunded` mapping associates each funder's address with the total amount they have contributed. When a new amount is sent, we can add it to the user's total contribution: ```js addressToAmountFunded[msg.sender] += msg.value; ``` ### Conclusion We have successfully implemented a system to track users who fund the `fundMe` contract. This mechanism records every address that is sending ETH to the contract, and maps the sender's address to the total amount they have contributed. ### 🧑‍💻 Test yourself 1. 📕 Explain why we need to use the mapping `addressToAmountFunded` inside the `fundMe` contract 2. 🧑‍💻 Implement a function `contributionCount` to monitor how many times a user calls the `fund` function to send money to the contract.