gistfile1.txt

contract Billboard{

	uint minimumBid = 10;
	uint minimumBidDelta = 10;

	Slot[] slots; //an array of slots. Each slot is one period of time (for example one day)

	struct Slot{
		address winner; // winner of the slot
		uint bid;		// amount of wei the winner bid
	}

	function getMinimumBidForSlot(uint _slotIndex) constant returns(uint){

		if(slots[_slotIndex].bid == 0){
			return minimumBid;
		}else{
			return slots[_slotIndex].bid+minimumBidDelta;
	    }
	}

}

Create using https://chriseth.github.io/browser-solidity/ and then try and getMinimumBidForSlot(10), it always returns 0x