Code

 Header...
// static demonstration

 double addup(double k){
   ... 

»  static int called;
»  static double sum;

»  sum+=k;
»  printf("k is %g new sum is %f\n", k, sum);
»  printf("The function has been called %d times\n", ++called);
  
»  return sum;
}

 int main(){
   ... 

»  int i, max=5;
»  double mysum;
  
»  for (i=1; i<=max; ++i) 
    mysum=addup(sqrt(i));
  
»  printf("The sum of the square roots of 1 to %d is %g\n", 
   max, mysum);
»  return 0;
}