Conceptual doubt regarding function as a parameter inside the other function

So I was solving a challenge named by Maximum circular sum and came across the solution https://ide.codingblocks.com/s/266931?_ga=2.208000087.459899190.1604214690-902027912.1603313363 . Here as the maxcircularsum function is being called inside the main , why haven’t we passed the kadane function as the parameter inside maxcircularsum function as we are calling kadane in maxcircularsum .
I’m confused as to when will we be using comparator function if this code is correct .
Please clarify my doubt .