Im getting the error as Undefined Reference when I included the #include in main.cpp

Question

Cube.cpp

#include "Cube.h"

double Cube :: getVolume() {

    return length_ * length_ * length_;

}

double Cube :: getSurfaceArea() {

    return 6 * length_ * length_;

}

void Cube :: setLength(double length) {

    length_ = length;

}

Cube.h

#pragma once

class Cube {

    public :
        double getVolume();
        double getSurfaceArea();
        void setLength(double length);

    private :
        double length_;

};

main.cpp

#include<iostream>
#include "Cube.h"

int main() {
    Cube c;

    c.setLength(3.48);
    double volume = c.getVolume();
    std::cout << "Volume: " << volume << std::endl;

    return 0;

}