Recursion in simple function

Question

I am having the following function:

void test(const char *nap){
if (*nap != 'D'){
    test(nap+1);
    std::cout << *nap;
}};

When I call the function with:

"ABCD"

Output, that I thought I would get was: ABC, however, in reality, its CBA. Can anyone explain to me where do I make mistake?

The stack unwinds and you're calling the recursion before printing. So, the first to print would be C, the stack unwinds one and prints B and so on. — ChiefTwoPencils
– ChiefTwoPencils, Commented Feb 3, 2016 at 20:02
@ChiefTwoPencils, oh, okay. I am C++ beginner, and had no idea that it works that way. — uksz
– uksz, Commented Feb 3, 2016 at 20:03
It's helpful to draw out on paper what's happening with the recursion when facing problems with its behavior. — ChiefTwoPencils
– ChiefTwoPencils, Commented Feb 3, 2016 at 20:03
@uksz - This video explains how recursion works youtube.com/watch?v=ygK0YON10sQ — vk239
– vk239, Commented Feb 3, 2016 at 20:04

anotherdev · Accepted Answer · 2016-02-03 20:03:02Z

4

You call it in the wrong order. Revert that:

test(nap+1);
std::cout << *nap;

like this

std::cout << *nap;
test(nap+1);

answered Feb 3, 2016 at 20:03

anotherdev

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Comments

Richard Chambers · Accepted Answer · 2016-02-03 20:03:27Z

Your recursion is to go to the end of the text string and to then go backwards printing each character.

In other words your function keeps calling itself until it reaches end of string. At that point it returns to where it called itself and the next step is to print the current character.

Then you return to where it called itself again and the next step is to print the current character.

The result is that you traverse the string until the end of string by the recursive calls. Once you reach the end of string you start unwinding the series of recursive calls. At each return you print the current character.

Try the following which will print the current character and then call itself to print the next character instead. When it reaches the end of the string it will unwind the recursive calls.

void test(const char *nap) {
    if (*nap != 'D'){
        std::cout << *nap;
        test(nap+1);
    }
};

Jay Kumar R · Accepted Answer · 2016-02-03 20:03:55Z

0

because the std::cout is after calling the recursion ( )..

test(nap+1);
std::cout << *nap;

That is parent feeds children before eating.

The below will get what you want:

 std::cout << *nap;
 test(nap+1);

answered Feb 3, 2016 at 20:03

Jay Kumar R

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