#include <stdexcept>
#include <iostream>

class Fridge
{
public:

    Fridge(float capacity)
        : capacity {capacity}, used {}
    {
        if (capacity < 0)
        {
            throw std::logic_error{"Fridge cant have negative space"}; 
        }
    }

    void add_stuff(float amount)
    {
        if (used + amount > capacity)
        {
            throw std::logic_error{"Fridge full. Cant add more!"}; 
        }

        used += amount;
    }

private:
    float capacity;
    float used;
};

int main()
{
    try
    {
        Fridge f {-1};
    }
    catch (std::logic_error& e)
    {
        std::cout << e.what() << std::endl;
    }

    Fridge f {8};
    f.add_stuff(3);
    f.add_stuff(3);

    try
    {
        f.add_stuff(3);
    }
    catch (std::logic_error& e)
    {
        std::cout << e.what() << std::endl;
    }
}