Understanding Recursion in C++🤔🤔

Question

Please can somehow explain how the following recursive function works, and why it outputs 01234 when 5 is passed as argument?

void calc(int x){
if(x > 0){
calc(--x);
cout << x;

}else{
return;
}
}

int main() {

calc(5);

Thanks.

Answer 1

Well, both are true. But it's important to understand exactly why. Here's what the computer does:
calc(5):
x > 0, so --x and calc(4):
x> 0, so --x and calc(3):
x > 0, so --x and calc(2):
x > 0, so --x and calc(1):
x > 0, so --x and calc(0):
x !> 0, so return to calc(1);
cout x of calc(1), which is 0; done with calc(1)
cout x of calc(2), which is 1; done with calc(2)
cout x of calc(3), which is 2; done with calc(3)
cout x of calc(4), which is 3; done with calc(4)
cout x of calc(5), which is 4; done with calc(5)
done with main, exit

Answer 2

because the recursive call comes before the cout, it'll finish the next calc() in line before it goes on to the cout step.
So when it does get to x=0, the if check fails, cout(0) returns, and it goes back to finish calc(1), where it prints x (which is 0 because of the --), and then with calc(1) done it goes back to finish calc(2), and so on

Answer 3

Thanks Orin Cook for the answer, but I still don't get it😅, do you mean the recursive call is evaluated untill it is false, then the function starts printing the values from cout in a reversed order?

Answer 4

Thank you Orin👍