Calculating Fibonacci Numbers Recursively in C

Question

I\'m trying to learn C by writing a simple program to output Fibonacci numbers. It isn\'t working.

fibonacci.h

unsigned int fibonacc         


        

Answer 1

Well, I preface that recursive function is not an efficient method to calculate Fibonacci and it may be used for dev training/demonstrations purposes only, because every recursion is stored in stack, and it may also overflow for large fibonacci numbers. It is rather worth the effort to write down a more efficient Fibonacci function that uses a loop, like following code:

#include 

#define MAX_ITERS 20


int fibonacci(int);

int main(int argc, char *argv[])
{
    unsigned int iters;

    if(argc>1) {
        iters=atoi(argv[1]);
    } else
        iters=MAX_ITERS;

    fibonacci(iters);

    return 0;
}

int fibonacci(int iterations)
{
   unsigned register int i;
   double first=0.0, second = 1.0, lastsum;
   printf("First %d iterations of Fibonacci series are :\n",iterations);

   for ( i = 0 ; i < iterations ; i++ )
   {
      if ( i <= 1 )
         lastsum = (double)i;
      else
      {
         lastsum = first + second;
         first = second;
         second = lastsum;
      }
      printf("%.0f\n",lastsum);
   }

}

Try to compare by your own, running ./fibonacci 50 with this method, for instance on a low cost processor (eg. on a Raspberry PI), and the one with the recursive functions and 50 first numbers as well, and see the difference! ,-)