Ethereum Cookbook

Fallback function

Each contract can have one unnamed function called the fallback function. It is executed if no other function matches the given signature or plain Ether is sent to the contract:

1. Create a fallback function by declaring an unnamed function:

function() {    // fallback function}

2. In order to receive Ether, mark the fallback function as a payable function. An exception will be thrown by the contract if it does not have a fallback function declared as payable:

function() payable {    // fallback function which can receive Ether}

A contract without a payable fallback function can still receive Ether as a result of self-destruct or mining. Such Ether transfers cannot be rejected by a contract and it is not recommended to use the contract ...