Here are some theory-based questions in the C++ programming language: 1. What is the difference between C and C++? 2. Explain the object-oriented programming (OOP) concepts in C++. 3. What are the basic data types in C++? 4. Describe the difference between pass-by-value and pass-by-reference in C++. 5. What is the difference between a class and an object in C++? 6. Explain the concept of inheritance in C++. 7. What are constructors and destructors in C++? 8. What is the purpose of the 'this' pointer in C++? 9. What is the difference between function overloading and function overriding in C++? 10. Explain the concept of templates in C++.