I have a simple test program in C++ that prints out attributes of a circle

#include <iostream>
#include <stdlib.h>
#include "hidden_functions.h" // contains the Circle class

using namespace std;

void print_circle_attributes(float r) {
    Circle* c = new Circle(r);
    cout << "radius: " << c->get_radius() << endl;
    cout << "diameter: " << c->get_diameter() << endl;
    cout << "area: " << c->get_area() << endl;
    cout << "circumference: " << c->get_circumference() << endl;
    cout << endl;
    delete c;
}

int main(int argc, const char* argv[]) {
    float input = atof(argv[0]);
    print_circle_attributes(input);
    return 0;
}

when I run my program with the parameter 2.4 it outputs:

radius: 0.0
diameter: 0.0
area: 0.0
circumference: 0.0

I've previously tested the program without the parameter, but simply using static values, and it ran just fine; so I know there's nothing wrong with the class I made...

So what did I do wrong here?

Note: the header is called hidden_functions.h because it served to test out how it would work if I had functions not declared in the header