hi guys i want to do the following code but it wont work

Code:
if(history[0][1] == NULL)
   printf("this worked");
basically what i want it to do is if the array history[0][1] has nothing in it (which i thought meant null) then i want want to do something. the compiler keeps giving me an error that i can use binary operators on history[0][1].

p.s the history array is of type struct history_entry which i have defined my self.