The **`ilogb` function** is a C library function that returns the exponent of a *floating point* argument as an integer.

The floating point is an alternative way to represent binary numbers with a fractional part. 

Every floating point number has three parts:

* Mantissa, which is the actual number.

* Sign, which is the sign (+/-) of the mantissa.

* Exponent, which sets the position of the binary point.

The following illustration shows the parts of a floating point number: 

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

# Syntax 
The `ilogb` function takes a single argument and returns a single value. We declare it as follows: 

# Parameter
The `ilogb` function takes a single argument of the `double` type. 

# Return value 
The `ilogb` function returns the exponent of the argument as a signed `integer.` 

* If the argument is *zero*, the return value is the `FP_ILOGB0` macro. The value of `FP_ILOGB0` is either `INT_MIN` or `- INT_MAX`.

* If the argument is *`NaN` (not-a-number)*, the return value is `FP_ILOGBNAN` macro. The value of `FP_ILOGBNAN` is either `INT_MIN` or `INT_MAX`. 

* If the argument is *infinite*, then `INT_MAX` is returned. 

> The value of `INT_MAX` is +2147483647. The value of `INT_MIN` is -2147483648. 


# Syntax 
The code below shows the use of the `ilogb` function in C:

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

int main() {
  //Declare values 
  int exp = 0; 
  double x  = -1.67812345e300;

  //Call the function 
  exp = ilogb (x);

  //Display the result 
  printf ("The exponent is: %d\n", exp);
  return 0;
}

What is ilogb() in C?

Returns the exponent of a floating-point argument as an integer from the C math library.