The **`signbit`** function in C determines whether a floating-point number is negative. 
>The signbit of a negative number is set as `1` 

This function checks if the given number's signbit is set. 
# Library
The `signbit` function can be accessed via the `math.h` library. 
```c
#include <math.h>
```
# Parameters
The `signbit` function only takes one parameter: the floating-point number that needs to be ascertained as negative. 
# Syntax
The syntax for the function call is:
```c
int returned_val = signbit(x);
```
# Return value
The function will return `0` if the floating-point parameter is non-negative (i.e., the signbit is not set). Otherwise, the number is negative and a non-zero number is returned. 
# Code


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

int main() {
  double num1 = 1.2;
  double num2 = -1.2;

  // signbit returns 0
  printf("num1 is %s\n", signbit(num1)? "negative" : "not negative");
  // signbit returns non-zero number
  printf("num2 is %s\n", signbit(num2)? "negative" : "not negative");

  return 0;
}

What is signbit in C?

Determines if a floating-point number is negative via math.h. Non-negative returns 0, negative returns non-zero.