Fibonacci Sequence in C

Question

This is the expected output:

We are to make a C program that calculates for the Fabonacci Sequence. We're only allowed up to 3 variables and we're NOT allowed to use loops. And I don't know what to do and how to start.

I hope you guys can help me. :/

Answer 1

Use recursion:

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Version in C/C++ language:

int fib(int a)
{
    if (a == 0) return 0;
    if (a == 1) return 1;
    return fib(a - 1) + fib(a - 2);
}

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Apply suggestion from this answer comments:

Version in C language:

/*
 * -1 is a error handler
 */
int fib(int a)
{
    if (a < 0 || a > 47) return -1;
    if (a == 0) return 0;
    if (a == 1) return 1;
    return fib(a - 1) + fib(a - 2);
}

Version in C++ language:

int fib(int a)
{
    if (a < 0) throw new std::out_of_range("Fibonacci is not defined for negative sign values.");
    if (a > 47) throw new std::overflow_error("Fibonacci for this value was overflow the integer.");
    if (a == 0) return 0;
    if (a == 1) return 1;
    return fib(a - 1) + fib(a - 2);
}

Answer 2

I would suspect that if you can't use loops that your professor/teacher intended you to use recursion. Otherwise it's simply a matter of looking up the proper formula, which makes no sense in a programming class.

If recursion is allowed I highly recomend reading this tutorial (assuming you aren't familiar with it).

Answer 3

http://mathworld.wolfram.com/BinetsFibonacciNumberFormula.html

which you can copy here

http://cboard.cprogramming.com/cplusplus-programming/108426-binets-formula.html

long double f(short N) {
    double phi = (1+pow(5,0.5))/2;
    return ceil((pow(phi,N) - pow(1-phi,N))/pow(5,0.5));
}

of course, it's just math, but it does calculate fib(N) without recursion and loops.. you still need a way to print all the values for fib(1)..fib(n) though

what your teacher wants is probably recursion.

Answer 4

If loops and recursion are not allowed, pick up fibonacci sequence definition and do it by hand... it is ridicolously boring and uninteresting but it is the most straightforward solution in those restrictions.

a = 0; // 0
b = 1; // 1
a = a + b; // 1
b = a + b; // 2
a = a + b; // 3
b = a + b; // 5

and so on: b holds the n-th and a the (n-1)-th number. (Copy-paste a = a+b; b = a+b; how many times you need...) Copy-pasting fragments of code is allowed?

... (edit) ...

Of course this answer just shows how ridicolous stuffs can get if we put too much rescrictions. If you don't know recursion, you have to learn it, definitively. Or stick into fine mathematics (as other answer shows), but recursion is a powerful tool programmers should know anyway, and the recursive approach is more intuitive than using mathemathical "tricks".

Answer 5

Since loop and recursion aren't allowed,

int fib(int n) {
   int fk1 = 0, fk0 = 1;
main_sub3:
   fk1 += fk0;
   fk0 = fk1 - fk0;
   if (n > 0) {
     -- n;
     goto main_sub3;

*raptor*

Answer 6

On the assumption that you are using 32 bit unsigned integers, the 48th Fibonacci number will cause an integer overflow. That makes it perfectly feasible to use a lookup table with all the values precalculated (by hand).

Answer 7

Recursion must be the answer dear! even i am an ameature and i think that recursion is the only other way to do that.

Answer 8

use http://www.research.att.com/~njas/sequences/b000045.txt as a data file ;)