Find the output.n=5

Question

int recur(int n)
{
return !n?0: recur(n-1)+1+recur(n-1);
}

Answer 1

n = 5
!n = false
Function returns recur(4) + 1 + recur(4)
Top level statement:
recur(4) + 1 + recur(4)
= 2 * recur(4) + 1

n = 4,
!n = false
Function returns recur(3) + 1 + recur(3)
Top level statement:
2 * (recur(3) + 1 + recur(3)) + 1
= 4* recur(3) + 3

n = 3
!n = false
Function returns recur(2) + 1 + recur(2)
Top level statement:
4* (recur(2)+1+recur(2)) + 3
= 8* (recur(2)) + 7

n = 2
!n = false
Function returns recur(1) + 1 + recur(1)
Top level statement:
8 * (recur(1)+1+recur(1)) + 7
= 16 * (recur(1)) + 15

n = 1
!n = false
Function returns recur(0) + 1 + recur(0)
Top level statement:
16 * (recur(0)+1+recur(0)) + 15
= 32 * (recur(0)) + 31

n = 0
!n = true
Function returns 0
Top level statement:
32 * (0) + 31
= 31

Ans : 31

Answer 2

would you explain once sirr

Answer 3

So for 0 the function returns 0.
otherwise it return 2*f(n-1) +1.
So you get:
0 -> 0
1 -> 1
2 -> 3
3 -> 7
4 -> 15
5 -> 31
Note​ the function will try work out the result in the reverse order and make recursive calls to get the answer. It will also make two calls​ for every level instead of doubling the number.

Answer 4

31. It's not too hard to work out by hand, or you can run it and see.