About base class in derived class initialization

Question

guys. I see several cases like:

class Derived:public Base{

public:
    Derived(...):Base(...){}
}

Is what situation or is there any principle

Answer 1

In case if we need to pass the arguments of derived constructor to the base constructor, it can be used.

class foo
{
    public:
        foo() {} 
        foo( int num ) {}
};

class bar : public foo
{
    public:
        bar(int barNum): foo(barNum) {}
};