The **`nearbyintl` function** is a C library function that rounds the argument's value to the nearest integer value. 

To use the `nearbyintl` function, we need to include the `math.h` header file, as shown below:
```C
#include <math.h>
```

# Syntax 
The `nearbyintl` function takes a single argument and returns a single value. It is declared as follows:

# Parameters
The `nearbyintl` function takes a single argument of the `long double` type. 

# Return Value
The `nearbyintl` function returns the nearest integer in the `long double` type format.

# Example
The code below shows the use of the `nearbyintl` function in C:

#include <stdio.h>
#include <math.h>

int main() {
  
  //Declare x
  long double x = 3.6890;

  //Call nearbyintl function
  long double ans = nearbyintl(x);

  //Display the result 
  printf ("The nearest integer is: %Lf\n", ans);

  return 0;
}

What is nearbyintl in C?

Rounds a long double to the nearest integer value, requiring the `math.h` header file.