How can I avoid re-initializing a variable when using recursion in c++?

Question

So I'm just starting to learn about recursion and I'm confused as to how avoid this problem. I will write a function that needs to store a variable, like a sum, but I have to declare the variable in the function so every time the recursive call is made the variable gets initialized again. How can I fix this? I think a helper function of some short but I'm not really sure.

int fib_tail(int n)
{    
    int fibResult = 0;
    int x = 0; // used for bottom-up approach
    if (n == 0) {
        return 0;
    }
    if (n == 1) {
        return 1;
    }
    if (n > 1 && x <= n) {
        fibResult += fib(x);
    }
    ++x;
    return fib_tail(n);
}

The variable accumulating the result is typically passed in as a parameter. — jdigital
– jdigital, Commented Oct 4, 2015 at 3:59
My bad for not providing an example. Here's an example of an attempt at making a tail recursive number for Fibonacci. — Matt
– Matt, Commented Oct 4, 2015 at 13:34

Dominique McDonnell · Accepted Answer · 2015-10-05 01:48:48Z

4

It would help if you provided your code. However usually you pass whatever you need in and return the result.

An example:

int Sum(Node* node)
{
    if (node == 0)
        return 0;
    return node->value + Sum(node->next);
}

Edit

Here is what I would do in your example:

int fib_tail(int n)
{    
    if (n <= 0) {
        return 0;
    }
    if (n == 1) {
        return 1;
    }
    return fib_tail(n-1) + fib_tail(n-2);
}

Ide one: http://ideone.com/hS2s38

edited Oct 5, 2015 at 1:48

answered Oct 4, 2015 at 4:00

Dominique McDonnell

2,52016 silver badges25 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

SkryptX Over a year ago

Why do you have a current-variable... this is not needed in any way... you even missed it yourself in your code while calling Sum :D

Dominique McDonnell Over a year ago

Haha, so easy to make simple errors when making an example. Thanks @SkryptX

Collectives™ on Stack Overflow

How can I avoid re-initializing a variable when using recursion in c++?

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related