Ethereum Cookbook

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Cap restrictions can be added to each individual also, and this allows the owner to have more control. To do this, create a mapping that stores the address as the key and cap as the value. Creating a mapping for contributions is also required:

mapping(address => uint256) public contributions; mapping(address => uint256) public caps;

Verify the individual cap for every token purchase to restrict users:

require(contributions[_beneficiary].add(_weiAmount) <= caps[_beneficiary]);

Create read-only methods for reading both the contributions and caps of an individual user:

function getUserCap(address _beneficiary) public     view returns (uint256) {     return caps[_beneficiary]; }function getUserContribution(address _beneficiary) public ...