[SOLVED] Problem in understanding fibonacci series using recursion in "C"

bikal · 06-15-2016, 08:53 PM

Can anyone tell me what is going on in this program that makes it display the fibonacci series.

Code:

#include <stdio.h>
int fibo(int a);
int main (void)
{
    int i;
    for(i=1;i<=5;i++)
    {
        printf("%d ",fibo(i));
    }
}
int fibo(int a)
{
    if(a==0)
        return 0;
    else if(a==1)
        return 1;
    else
        return (fibo(a-1)+fibo(a-2));
}

grail · 06-15-2016, 11:53 PM

Do you not understand what the fibonacci sequence is or you do not understand recursive functions?? Either can be found with a simple search.

As far as the code goes, there are no complicated commands or functions, so if you really do not follow it you may need to take a course in C programming

sundialsvcs · 06-16-2016, 07:00 AM

Notice, in particular, how the fibo function calls itself.

A common, common-sense description of this number series is "naturally recursive," and the fibo function is a direct implementation of that definition. The definition of the first two numbers is fixed. The definition of any and every subsequent number in the series is defined as the sum of the numbers that preceded it. (The series can be calculated recursively, or as a simple loop.)

"Towers of Hanoi" is another commonly-used textbook demonstration of recursion.

bikal · 06-16-2016, 07:57 PM

Sorry but I think that wasn't a helpful reply. The problem is I cannot understand the recursive nature of this program

Ser Olmy · 06-16-2016, 08:20 PM

Quote:

Originally Posted by bikal

Sorry but I think that wasn't a helpful reply. The problem is I cannot understand the recursive nature of this program

I think the reply was pretty helpful. Assuming you know that each digit in the Fibonacci sequence is the sum of the two previous digits, it should be pretty clear how it works.

The "fibo" function simply returns the number corresponding to a given position in the sequence by finding the sum of the two previous digits, and it does so by means of recursion, except for positions 0 and 1 which are treated as special cases:

fibo(0) and fibo(1) will return 0 or 1 respectively
fibo(2) will return the sum of fibo(1) and fibo(0)
fibo(3) will return the sum of fibo(2) and fibo(1)

...and so on.

This is a classic example of recursion, and you can do this with pretty much any problem that can be split into two parts, where one part ends up being just a smaller version of the original problem. For instance, a digit sum can be described as the value of the first digit plus the digit sum of the remaining digits.

NevemTeve · 06-16-2016, 11:27 PM

> The problem is I cannot understand the recursive nature of this program.

That's sad. And what could be done to remedy this situation?

sundialsvcs · 06-17-2016, 09:28 AM

What's there to "understand?" Recursion is defined as: "a function calls itself."