Using return; in recursion functions

Question

#include <stdio>
using std::cout;
void CountDown(int N) {
  if(N == 0) {
    return;
  }
  cout << N;
  CountDown(N-1);  
  //return;
}

In the code the output I get when return is commented is same as when not commented.

What I want to ask is whether it makes a difference if I use a return; statement at the end of the function (since it would implicitly return to the function, which called it, at the end of the braces)?

Another question: What if had a function with a return type instead of void here. I tried it with a function. The value was wrong.But there was no compiler error. So using simply a return; makes no difference right? Except when I want to prematurely end the function right?

It makes no difference whether you put return; at the end of a function returning void. This has nothing to do with recursion, it is always true. — Jonathan Wakely
– Jonathan Wakely, Commented Sep 2, 2015 at 14:17
Mmm. In that code, the last return; is never reached, isn't it? But in any case, that sentence is no necessary in void functions. — Tarod
– Tarod, Commented Sep 2, 2015 at 14:18
Re updated question, falling off the end of a value returning function is undefined behavior see this question ... because it is undefined behavior no diagnostic is required. — Shafik Yaghmour
– Shafik Yaghmour, Commented Sep 2, 2015 at 14:34
@ShafikYaghmour I didn't get it.What does undefined behaviour mean.And how does it affect the program? I mean its not a compiler error right? — user2546419
– user2546419, Commented Sep 2, 2015 at 14:41

Mr. Llama · Accepted Answer · 2015-09-02 14:17:21Z

4

For void return functions, no it doesn't make a difference. However, if the function is expected to return anything but void, then you'll need to include a valid return for all code paths.

answered Sep 2, 2015 at 14:17

Mr. Llama

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4 Comments

463035818_is_not_an_ai Over a year ago

There is no code path that would reach beyond the call to CountDown(N-1)

463035818_is_not_an_ai Over a year ago

well, your answer is of course still correct, I just thought one might misunderstand it

user2546419 Over a year ago

@tobi303 why not? I mean when (n==0) case would be done and that function will return to the function CountDown(1) then the return; statement would be executed right?After the calling CountDown(0) part.

463035818_is_not_an_ai Over a year ago

hm yes you are right. I faster in writing than thinking, my mistake

NathanOliver · Accepted Answer · 2015-09-02 14:18:21Z

2

At the end of a void function control is automatically returned to the calling function so you do not need a return; at the end. return in a void function is used to exit the function before it normally would like in your if statement.

If you have a function that is supposed to return a value and does not then that is undefined behavior.

answered Sep 2, 2015 at 14:18

NathanOliver

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