error: no matching function for call to

Question

Heres my error...

"In constructor 'NumGame::NumGame(int&)': error: no matching function for call to 'Category::Category()'"

Ive looked at a few similar questions here but cant seem to find an answer. I have a base class Category and NumGame is inherited from it but wont compile.

class Category {

public:
    void virtual selection(int&);
    Category(int&);
    virtual ~Category(){};
private:
    int myRandNum;
};

Category::Category(int& a){
    myRandNum = a;
}

void Category::selection(int& a){
    cout << "I am NumGame version number... " << a << endl;
    cout << "Now Im playing... " << myRandNum << endl;
}

class NumGame : public Category {

public:
    void selection(int&);
    NumGame(int&);
    ~NumGame(){};
private:
    int myRandNum;
};

NumGame::NumGame(int& b){
    myRandNum = b;
}

void NumGame::selection(int& b) {

}

Answer 1

Reason for the error:

When you create an instance of derived class NumGame the Base class Category no argument constructor is called to create the Categorypart of the object. Your class doesn't have one and the compiler complains about it.

Why the compiler did not synthesize the default constructor?

Once you provide any constructor for your class the compiler does not synthesize the constructor which does not take any argument for you, You have to provide that yourself if your code uses one.

Solutions:

There are two ways to avoid the error:

Call the appropriate available constructor in Base class Catoegory subobject through Member Initializer list. This removes the scenario where your code uses a no argument constructor.

NumGame::NumGame(int& b) : Category(b)
{

}

OR

You need to provide a no argument constrcutor for Category class yourself:

Category::Category()
{

}

Answer 2

Category does not have a default constructor, so you need to supply arguments when constructing the Category base object of NumGame:

NumGame::NumGame(int& b) :
    Category(b)
{
    myRandNum = b;
}