These are 2 slightly different versions of a recursive program for factorial :-
Code:int fact(int x) { if(x == 1) return 1; else return x * fact(x--); }The first one results in a stack overflow with the recursive calls being :-Code:int fact(int x) { if(x == 1) return 1; else return x * fact(--x); }
(for say, x = 5)
rec(5)
rec(4)
rec(4)
rec(4)...
The second one gives an output neglecting the starting value of x.
Can anyone shed some light please ? Thanks.
Postfix decrement returns the x before the subtraction, prefix decrement does not.
I still don't get itOriginally Posted by whiteflags
AS whiteflags said, there is a difference between pre and post decrement.
Because of that difference, your first is (roughly) functionally equivalent to
which is infinitely recursive (and decrementing of x is never executed). The second is functionally equivalent toCode:int fact(int x) { if(x == 1) return 1; else { return x * fact(x); --x; } }
which, because it decrements x BEFORE calling fact() recursively, is not infinitely recursive.Code:int fact(int x) { if(x == 1) return 1; else { --x; return x * fact(x); } }
Note that your second version will also be infinitely recursive if supplied with a negative argument.
Got it...Thanks a lot guys !
