Ethereum Cookbook

How to do it…

1. Create a mapping variable to store the address as a key and whitelisting status as the value. Marking the mapping as a public variable will create a getter function that can be used to verify the whitelist status:

mapping(address => bool) public whitelist;

2. Create a function to add users to the whitelisting contract. This function should be restricted to the owner or admin:

function addToWhitelist(address _investor) external     onlyOwner {     whitelist[_investor] = true; }

3. For easy whitelisting, you can have another function that accepts an array of addresses:

function addMultipleToWhitelist(address[] _investors)     external onlyOwner {         for (uint256 i = 0; i < _investors.length; i++) {             whitelist[_investors[i]] = true;         }}