nextafter() and nexttoward() in C/C++

How would you solve below problems in C/C++?

• What is the smallest representable positive floating point number in C/C++?
• What is the largest representable negative floating point number in C/C++?
• Given a positive floating point number x, find the largest representable floating point value smaller than x?

nextafter(x, y) and nexttoward(x.y) In C and C++, both nextafter(x, y)  and nexttoward(x.y)  are similar functions defined in math.h or cmath header files. They both return next representable value after x in the direction of y. nexttoward() has more precise second parameter y. The following program demonstrates the concept : 

CPP

// C program to demonstrate use of nextafter() and
// nexttoward()
#include <math.h>
#include <stdio.h>
int main()
{
    // using nextafter
    printf("Smallest positive floating point number : %e\n",
           nextafter(0.0, 1.0));
    printf("Largest negative floating point number :%e\n",
           nextafter(0.0, -1.0));
    printf("Largest positive floating point number smaller "
           "than 0.5 : %e\n",
           nextafter(0.5, 0.0));

    // using nexttoward
    printf("Smallest positive floating point number : %e\n",
           nexttoward(0.0, 1.0));
    printf("Largest negative floating point number : %e\n",
           nexttoward(0.0, -1.0));
    printf("Largest positive floating point number smaller "
           "than 0.5 : %e\n",
           nexttoward(0.5, 0.0));
    return (0);
}

Output

Smallest positive floating point number : 4.940656e-324
Largest negative floating point number :-4.940656e-324
Largest positive floating point number smaller than 0.5 : 5.000000e-01
Smallest positive floating point number : 4.940656e-324
Largest negative floating point number : -4.940656e-324
Largest positive floating point number smaller than 0.5 : 5.000000e-01

Time Complexity: O(1)
Auxiliary Space: O(1)