## fib.cpp

 Up: Keywords
```/*
* fib.cpp
*
* Time how long it takes to calculate a Fibonacci number. See
* http://en.wikipedia.org/wiki/Fibonacci_number for information about the
* Fibonacci sequence. This application demonstrates the use of the cilk_spawn
* and cilk_sync keywords.
*
* This program takes a single parameter to specify the number of workers to
* be used in the calculation. If not specified, Intel Cilk Plus will query
* the operating system to determine the number of cores on the system and use
* that many workers.
*/

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <cilk/cilk.h>
#include <cilk/cilk_api.h>

int fib(int n)
{
if (n < 2)
return n;
int x = cilk_spawn fib(n-1);
int y = fib(n-2);
cilk_sync;
return x + y;
}

int main(int argc, char *argv[])
{
// Fibonacci number to be calculated.  39 is big enough to take a
// reasonable amount of time
int n = 39;

// If we've got a parameter, assume it's the number of workers to be used
if (argc > 1)
{
// Values less than 1, or parameters that aren't numbers aren't allowed
if (atoi(argv) < 1)
{
printf("Usage: fib [workers]\n");
return 1;
}

// Set the number of workers to be used
__cilkrts_set_param("nworkers", argv);
}

// Time how long it takes to calculate the nth Fibonacci number
clock_t start = clock();
int result = fib(n);
clock_t end = clock();

// Display our results
double duration = (double)(end - start) / CLOCKS_PER_SEC;
printf("Fibonacci number #%d is %d.\n", n, result);
printf("Calculated in %.3f seconds using %d workers.\n",
duration, __cilkrts_get_nworkers());

return 0;
}
```
 Up: Keywords