Why does it return 5?

Question

#include <iostream>
using namespace std;

int r(int a)
{
if (a)
return r(a + 1) + 1;
else
return 0;
}

void main()
{
int f = -5;
cout << r(f);
}

I would like to know why it returns 5.
I used the debugger to see how it works and once it reaches 0, automatically returns 5 and I don't understand why. Could someone explain it, please?
Thanks in advance!

Answer 1

Each iteration adds 1 to the result returned. So the last iteration of the function returns 0. The second returns r(a+1) + 1. r(a+1) is 0. So it returns 1. And so on.

Answer 2

Winter Soldier
the answer is in the 'r' function.
It is a recursive function that will receive an int.
If the int is equal to 0 (zero) it stops the recursion and return what it had until now + zero.
The next recursion will add 1 to the result and to the parameter.
Here is what is happening in each recursion: (imaginary result variable starts at zero)

a = -5 (result) +1
a = -4 (result) +1
a = -3 (result) +1
a = -2 (result) +1
a = -1 (result) +1
a = 0 (result) +0 recursion stops
------------------------------------
total (result )=5

Hope you understand my explanation.

Answer 3

I got it. Thanks a lot!