Thread: Recursive Fibonacci, some help needed

Hey guys,

This is a hmwk problem of mine that I've been caught up in for a while now.... I need some suggestions to help me figure out what I'm missing, I'm sure it's a minor detail...

Just so I get everyone on the same page :

-This program needs to request from the user the 'x' number or Fibonacci numbers that need to be printed.

-Uses a recursive function to compute the fist 'x' fibonacci numbers

- Prints the first 'x' fibonacci numbers.

Here is what I have up to this point. (I HAVE looked at other examples on this site, but they differ from what I am trying to do... I do not like to blend other codes into mine, as it leads to confusion on my end, and I do want to know what the hell is going on. Any help would be great, thx guys.)

You will notice I have commented a while loop and index with question marks.... I really don't know if I need these or not, all I know it that i can't get my fibonacci functions to print out... (I am limiting the user to enter only the 1st 20 numbers)

I am pretty sure my function is correct, but my main function is screwy...

Code:

#include<stdio.h>

double fib(int num)
{
	if(num<0) {
		return 0;
	}
	else if(num==0) {
		return 1;
	}
	else if(num<=20) {
		return (fib(num-1)+fib(num-2));
	}
	else {
		printf("The integer you gave is too large\n");
		return 0;
	}
}

int main()
{
	double num;
	/* ?? int index=0; ?? */
	
	printf("Give an integer from 0 to 20:");
	scanf("%d", &num);

	/* ??? while(num>=0)
			index++; 	??? */
	
	printf("The first %d fibonacci numbers are:\n", num);
	printf("fibonacci(%d) = %1.01f\n", num, fib(num));
}

Your method is completely flawed conceptually seen. Fib number n is equal to fib numbers n-1 + fib number n-2, not the two numbers below it added together.

Difference?

First few fib numbers:

1 1 2 3 5 8

8 = 5 + 3

Not 7 + 6.

Wikipedia has some info on it. Look it up - If I'm not wrong, they might actually have a recursive example. If not, well, there are ........loads on the web anyway. It's a popular way to teach recursion.

Okay, I'm not the C programming master, but would somethng like this work

Code:

#include <stdio.h>

unsigned long fib(unsigned n)
{                             
  if (n > 2)
    return (fib(n - 1) + fib(n - 2));
  else
    return 1;
} 

int main(void)
{
  int i=0;
  int num;
  unsigned long val;

  printf("Give an integer from 0 to 20:");
  if((scanf("&#37;d", &num))!=1)
    printf("input error\n");
  if(num > 20){
    printf("outside of range\n");
    return 0;
  }
  for(i=1; i<num+1; i++) {
    val = fib(i);
    printf("The fibonacci numbers are:%u\n", val);
  }

  return 0;
}

Well, first of all I want to say "Hi" to all members at this community. Here is mine solution:

Code:

int F(int n) {
if (n <= 1)
return 1;
else
return F(n-2) + F(n-1);
}

F is function calculating fibonnaci number.

Thanks for the advise guys, I did get the program to run. I was not aware that I had a lot missing. Took me a couple hours of toying around with it, but it came out. Thanks again.

Originally Posted by IceDane

Your method is completely flawed conceptually seen. Fib number n is equal to fib numbers n-1 + fib number n-2, not the two numbers below it added together.

Which is not what the code is doing. The code, as far as computing Fibonacci numbers, is correct.