What is llround() function in C++?

#include <iostream>
#include<math.h>  
using namespace std;
int main() {
  double number = 380.555;
  cout <<"The number is :" << number << endl;
  cout << "The llround() is :"<< llround(number) << endl;
  return 0;
}

#include <iostream>
#include<math.h>  
using namespace std;
int main() {
  float number = 10.5;
  cout <<"The number is :" << number << endl;
  cout << "The llround() is :"<< llround(number) << endl;
  return 0;
}

#include <iostream>
#include<math.h>  
using namespace std;
int main() {
  long double number = 340.333333;
  cout <<"The number is :" << number << endl;
  cout << "The llround() is :"<< llround(number) << endl;
  return 0;
}