unsigned int fibonacci_closed(unsigned int n) {
 double term_number = (double) n;
 double golden_ratio = (1 + sqrt(5)) / 2;
 double numerator = pow(golden_ratio, term_number);
 return round(numerator/sqrt(5));
}

1>ClCompile:
1>  fibonacci_closed.c
1>c:usersodpdocumentsvisual studio 2010projectsfibonaccifibonaccifibonacci_closed.c(7): warning C4013: 'round' undefined; assuming extern returning int
1>fibonacci_closed.obj : error LNK2019: unresolved external symbol _round referenced in function _fibonacci_closed

static inline double round(double val)
{
    return floor(val + 0.5);
}

double round_replace(double val) {
  if (val > 0.0) return floor(val + 0.5);
  if (val < 0.0) return ceil(val - 0.5);
  return val;
}

round_replace(inf) --> inf
round_replace(1.5) --> 2
round_replace(1.1) --> 1
round_replace(0.9) --> 1
round_replace(0.5) --> 1
round_replace(0.4) --> 0
round_replace(0.1) --> 0
round_replace(0) --> 0
round_replace(-0) --> -0
round_replace(-0.1) --> -0
round_replace(-0.4) --> -0
round_replace(-0.5) --> -1
round_replace(-0.9) --> -1
round_replace(-1.1) --> -1
round_replace(-1.5) --> -2
round_replace(-inf) --> -inf