Campaign.sol

pragma solidity ^0.4.0;

contract Campaign {

    enum States 
    { 
        inprogress,
        success,
        fail
    }
    
    // get the current campaign stage
    function state() public constant returns (uint256)
    {
        return uint256(States.inprogress);
    }

    // if the current state does not equal the expected one, throw
    modifier atStage(States _expectedState) 
    {
        if (state() != uint256(_expectedState)) 
        {
            throw;
        }
        else 
        {
            // continue with state changing operations
            _;
        }
    }
  
    // must be at state inprogress
    function contribute() public atStage(States.inprogress) 
    {
        //put your code here
    }
    
    //todo genere other transitions function ...
}