Can someone explain how the output is what it is?

[TinnyMintz]

So I have the this code:

#include<iostream>​
using namespace std;​

void fun(int x) {​

  if(x > 1) {​

    cout << --x << " ";​

    fun(--x);​

    cout << x << " ";​

  }​
}​

 ​

int main() {​

  int a = 5;​

  fun(a);​

  return 0;​
}

Which gives me an output of 4 2 1 3, but I am not sure why, its the correct answer but Im trying to understand how its getting those numbers from just 5, can someone explain it to me if possible?

[jonnin]

well, you call it with 5, it is -- to 4 and printed. Then you call it with --4, which is 3.
fun called with 3 is > 1, so --3 is 2, print 2, .... can you follow how that happens and continue from here?

maybe a better question is, can you follow a more normal recursion function through? Do you understand how the inefficient recursive factorial works?

[TinnyMintz]

Oh okay I understand that but how do you get 3 in the end? Is it from when you get --4 and it just saves it or something?

[jonnin]

Add print statements and you will see it.

#include<iostream>
using namespace std;

void fun(int x) {

  if(x > 1) {

    cout << "printing x-1 "<< --x << " " << endl;
    cout <<"calling fun " << x-1 << endl;
    fun(--x);

    cout <<"printing x " << x << endl;

  }
}

 

int main() {

  int a = 5;

  fun(a);

  return 0;
}