If you're having trouble with one test case, I know I did. The solution was to notice that the Calculate function returned a long long. This made me think that one test case was really large. I changed the private variables to long instead of ints and it worked. Hope this helps!

All test case passed!

class Box{
    private:
    int l, b, h;
    public:
    Box(){
        l = 0;
        b = 0;
        h = 0;
    }
    Box(int length, int breadth, int height){
        l = length;
        b = breadth;
        h = height;
    }
    Box(const Box& B){
        l = B.l;
        b = B.b;
        h = B.h;
    }
    
    int getLenght(){
        return l;
    }
    int getBreadth(){
        return b;
    }
    int getHeight(){
        return h;
    }
    long long CalculateVolume(){
        return (long long)l*b*h;
    }
    
    friend bool operator < ( Box&A,Box& B){
        if( (A.l < B.l) || ((A.b < B.b) && (A.l == B.l)) || ((A.h < B.h) && (A.l == B.l) && (A.b == B.b)) ){
            return true;
        }else{
            return false;
        }
    };
    
    friend ostream& operator<< (ostream& output, const Box& B){
        output << B.l << " " << B.b << " " << B.h;
        return output;
    }
};

I don't understand what this problem helped me learn. Bad code practice let you pass test cases.

This is a bad practice: ostream& operator<<(ostream& out, Box B) The second parameter should be const Box& B. Otherwise, you are invoking the copy constructor in a place where it is not necessary.

This is the reason some people get 4 instead of 7 for the sample test case.

Also, all those getXX() functions are missing the const qualifier at the end.

To overload operator <<, I use the following code

ostream& operator<<(ostream& out, const Box& B){ return out << B.l << " " << B.b << " " << B.h; }

But the system says "std::ostream& Box::operator<<(std::ostream&, const Box&)’ must take exactly one argument". Can anyone help me with this problem? Thanks in advance.