为什么 OddSeq 和 SquareSeq 未定义？

问：

我是否需要使用 #include 来定义这些变量？我想知道为什么我收到一个错误，说它们未定义。除此之外，我相信该程序是按照我想要的方式推出的。

#include <iostream>
#include <string>


using namespace std;

class AbstractSeq {
public:
    virtual void test() = 0;

    int main() {

        OddSeq odd;
        SquareSeq sq;
        int k;
        int m;
        

        cout << "Enter the lower bound integer k: ";
        cin >> k;

        cout << "Enter the upper bound integer m: ";
        cin >> m;

        cout << "The terms of the odd numbers sequence are: " << endl;
        odd.printSeq(k, m);

        cout << "Their sum is: ";
        cout << odd.sumSeq(k, m);



        cout << "The terms of the square numbers sequence are: " << endl;
        odd.printSeq(k, m);

        cout << "Their sum is: ";
        cout << sq.sumSeq(k, m);
        return 0;
    }

};