Recursive calls in void function

Question

I run this C++ code and it prints "ABACABA" on the screen.Can someone give me a detailed explanation of how recursive calls work in this example? I can`t understand why i get that output.

#include <iostream>
using namespace std;

void f( char c)
{
    if (c > 'A') f(c-1);

    cout << c;

    if (c > 'A') f(c-1);

}

int main()
{
    f('C');
}

Do you have a debugger you could step through it in? Or indeed drawing in a notebook? — Jon Hanna, Jul 23 '18 at 15:24
What does `f('A')`? Same question for `f('B')`, and finally `f('C')`. — Jarod42, Jul 23 '18 at 15:25
I don`t understand what that line after the cout does.I mean what is the order functions get called? — user9163287, Jul 23 '18 at 15:28
Possible duplicate of [Understanding how recursive functions work](https://stackoverflow.com/questions/25676961/understanding-how-recursive-functions-work) — Killzone Kid, Jul 23 '18 at 15:31
I've enriched your code a bit: [Demo on coliru](http://coliru.stacked-crooked.com/a/b7071f880d5acff6). Does this help? — Scheff's Cat, Jul 23 '18 at 15:31
The order in which they get called is f('C') f('B') f('A') f('A') f('B') f('A') f('A') — Beta, Jul 23 '18 at 15:34
Translate it to a "mathematical" function: `f(C) = f(B) C f(B) = f(A) B f(A) C f( A ) B f( A ) = 0 A 0 B 0 A 0 C 0 A 0 B 0 A 0 = ABACABA` — zdf, Jul 23 '18 at 17:03

schorsch312 · Answer 1 · 2018-07-23T16:58:34.350

2

The ansi char "C" decremented is "B". C-- == B
The ansi char "B" decremented is "A". B-- == A

For the comparison:

B>A
C>A
C>B

I think you can follow the logic better, if you introduce a second std::cout as

#include <iostream>

void f(char c) {
    std::cout << " start " << c << "\n";
    if (c > 'A')
        f(c - 1);
    std::cout << c;
    if (c > 'A')
        f(c - 1);
}

int main() {
    f('C');
    return 0;
}

The output than reads as:

 start C
 start B
 start A
AB start A
AC start B
 start A
AB start A
A

I also suggest, that you use a debugger to do tasks like that.

edited Jul 23 '18 at 16:58

answered Jul 23 '18 at 15:37

schorsch312

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Pedantically `'A' + 1` is not guarantied to be `'B'`. (true for ansi and also for EBCDIC). – Jarod42 Jul 23 '18 at 16:22

Recursive calls in void function

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