SRL Archive - C/C++ Help and Tutorials

I'm supposed to 'Write a program that reads a positive integer n entered by the user and then computes and displays the corresponding Fibonacci number"

Here's what I have so far

/* This program displays the fibonacci number of the user's input*/ 

#include "stdafx.h"
#include "simpio.h"
#include "genlib.h"
#include <math.h>

int fibonacci(int num);
int main()
{
	int input, fibnum;
	printf("Input a positive integer to calculate the fibonacci of: ");
	input = GetInteger();
	fibnum=fibonacci(input);
	printf("f(%d) = %d\n", input, fibnum);
}
int fibonacci(int num)
{
	int num1, num2, fibnum, i;
	num1 = 0;
	num2 = 1;
	if (num  == 0)
	{
		return(0);
	}
	if (num == 1)
	{
		return(1);
	}
	i = 1;
	while (i != num)
	{
		fibnum = num1+num2;
		num1 = num1+num2;
		i+=1;
		while (i != num)
		{
			fibnum = num1+num2;
			num2=num1 + num2;
			i+=1;
		}

	}
	return(fibnum);
}

It works fine for up to 4, but then at 5 it starts messing up. I've been trying to get it to work for about an hour now (from scratch I mean) and my head hurts O_o Any hints or tips would be appreciated…

try this

int fibonacci(int index) {
    if(index == 0)
        return 0;
    int one = 1;
    int two = 1;
    for(int i = 0; i < index; i++) {
        int cache = two;
        two = two + one;
        one = cache;
    }
    return two;
}

havent actually tested

edit: just so i dont have to imagine it, heres the sequence
1 1 2 3 5 8 13 21

Tested it, doesn't work. It gives f(1) = 2, f(2) = 3, f(3) = 5. I'll see maybe there's some small bug causing it to mess up…

EDIT: Ah, using a third var gives me an idea, lets see if I can make it work…

EDIT: My idea didn't work :(

EDIT:

Redid it, can't figure out for the life of me why this won't work…

/* This program displays the fibonacci number of the user's input*/ 

#include "stdafx.h"
#include "simpio.h"
#include "genlib.h"
#include <math.h>

int fibonacci(int num);
int main()
{
	int input, fibnum;
	printf("Input a positive integer to calculate the fibonacci of: ");
	input = GetInteger();
	fibnum=fibonacci(input);
	printf("f(%d) = %d\n", input, fibnum);
}
int fibonacci(int num)
{
	int num1, num2, num3, fibnum, i;
	num1 = 0;
	num2 = 1;
	if (num  == 0)
	{
		return(0);
	}
	if (num == 1)
	{
		return(1);
	}
	i = 1;
	while (i != num)
	{
		fibnum = num1 + num2;
		num1 = num1 + num2;
		i+=1;

		while(i != num)
		{
			fibnum = num1 + num2;
			num2 = num1 + num2;
			i+=1;
		}
	}
	return(fibnum);
}

Ops, nvm that's the same thign as I had in first post -.-

Try this, it does work (tested it myself)

Then explain to your teacher why you dynamically allocated memory… :D

unsigned long int fib(unsigned int num)
{
   int i = 1;
   unsigned long int value = 0;
   unsigned long int* fibarray;
   fibarray = (unsigned long int*) calloc(num + 1, sizeof(unsigned long int)); // Potentially create a memory leak

   fibarray[0] = 0;
   fibarray[1] = 1;  // Prime the pump, so to speak

   while(i < num)
   {
      fibarray[i + 1] = fibarray[i] + fibarray[i - 1];
      ++i;
   }

   value = fibarray[num];
   free(fibarray); // Avoid a memory leak
   return value;
}

Here is another version that doesn't use an array. Probably better for this assignment.

unsigned long int fib(unsigned long int num)
{
  unsigned long int first = 0;
  unsigned long int second = 1;
  unsigned long int third = num;

  for(int i = 1; i < num; ++i)
  {
     third = second + first;
     first = second;
     second = third;
  }
  return third;
}

And here is the recursive solution *WARNING* WAY SLOW!

unsigned long int fib(unsigned long int num)
{
   if (num == 0)
      return 0;
   else if (num == 1)
      return 1;
   else
      return fib(num - 2) + fib(num - 1);
}

Hope that gives you a feel for how to do this.

Ops, forgot to post that I solved it :( Sorry you had to do that work :p I ended up doing something like your second method.