I cant understand this code!!

[Black cpp]

I download the tutorial in this site.I got a proplems in understanding this code

#include <iostream> // factorial calculator
using namespace std;
int add (int a) // proplems start here
{
    if (a>1)
    return a*add (a-1); //this is the big proplem
    else return 1;
} // end here
int main ()
{
int x;
cin >> x;
cout << add (x);
return 0;
}

i want someone to tell me how this code work.
please answer my question fast

[Computergeek01]

What do you want to know? It takes input from the user on line 12 and passes it to the add(...) function on line 13. From here the code executes Line 3 through Line 8. Do you have a specific question?

[Black cpp]

i mean in return a*add (a-1);
for ex
the user entered 5 the value return is 120 how???why???
i think it should return the value 20 <<5*4=20>>

[Kyon]

For 5, the function returns this:

5*add(5-1) = 5*add(4)

For 4, this function returns:
4*add(3)
3: 3*add(2)
2: 2*add(1)
1: 1

So 5 returns:

5*add(4) = 5*4*add(3) = 5*4*3*add(2) = 5*4*3*2*add(1) = 5*4*3*2*1 = 120

[blackcoder41]

Please take time to study this. I hope it helps. Try visualize smalls numbers like 1, 2 and 3 first.

add(5) = 5*add(4)
           add(4) = 4*add(3)
                      add(3)= 3*add(2)
                                add(2) = 2*add(1)
                                           =1
                                2      = 2*1
                      6     = 3*2
           24     = 4*6
120    = 5*24

[edit]
Too slow..

[Black cpp]

thanx.
but why stop in 1??
why it dosnt complete to 0 then -1
if its because (if) it should return 1 because

if (a>1).....
else return 1; 

[Zhuge]

It is returning 1. It's just then being multiplied by all the previous numbers you had been returning. blackcoder's chart can help you see that.