C++: Practice: OOP Comprehensive

Q: Q: Why use pointers to store students?

A: To achieve polymorphism. Using vector would cause object slicing, so only base class methods could be called.

Q: Q: What about memory leaks?

A: Use smart pointers (unique_ptr) to automatically manage memory — no need for manual delete.

Last updated: 2026-08-26

In the previous 35 lessons, we've covered many aspects of C++.

Now, it's time to put it all together.

In this lesson, we'll build a complete student management system — from requirements analysis to code implementation, experiencing real software development.

1. Project Requirements Analysis

(1) 1.1 Functional Requirements

The student management system we're building has the following features:

Feature Module	Specific Functions
Student Management	Add, delete, modify, search students
Grade Management	Enter grades, calculate averages, ranking
Data Persistence	Save to file, load from file
User Interface	Menu-driven console interface

(2) 1.2 Class Design

Based on the requirements, we need to design the following classes:

TEXT 📖 Display only

Student (Base class)
 ↑ Inherits
UndergraduateStudent (Undergraduate)
GraduateStudent (Graduate student)

Course (Course class)
Grade (Grade class)

ManagementSystem (Management system class)
 - vector<Student*> students
 - vector<Course> courses

2. Basic Version Implementation

(1) 2.1 Student Class Design

Example: Student Class Basic Version (Difficulty ⭐⭐)

TEXT 📖 Display only

#include <iostream>
#include <string>
#include <vector>

// Student base class
class Student {
protected:
	std::string id; // Student ID
	std::string name; // Name
	int age; // Age
	std::string major; // Major

public:
	// Constructor
	Student(const std::string& id, const std::string& name, int age, const std::string& major)
	: id(id), name(name), age(age), major(major) {}
	
	// Virtual function: display info
	virtual void display() const {
		std::cout << "Student ID: " << id << std::endl;
		std::cout << "Name: " << name << std::endl;
		std::cout << "Age: " << age << std::endl;
		std::cout << "Major: " << major << std::endl;
	}
	
	// Virtual destructor
	virtual ~Student() {}
	
	// Getter
	std::string getId() const { return id; }
	std::string getName() const { return name; }
};

// Undergraduate class
class UndergraduateStudent : public Student {
private:
	int year; // Year (1-4)

public:
	UndergraduateStudent(const std::string& id, const std::string& name, 
					int age, const std::string& major, int year)
	: Student(id, name, age, major), year(year) {}
	
	void display() const override {
		Student::display();
		std::cout << "Year: " << year << std::endl;
		std::cout << "Type: Undergraduate" << std::endl;
	}
};

// Graduate student class
class GraduateStudent : public Student {
private:
	std::string advisor; // Advisor

public:
	GraduateStudent(const std::string& id, const std::string& name,
				int age, const std::string& major, const std::string& advisor)
	: Student(id, name, age, major), advisor(advisor) {}
	
	void display() const override {
		Student::display();
		std::cout << "Advisor: " << advisor << std::endl;
		std::cout << "Type: Graduate Student" << std::endl;
	}
};

(2) 2.2 Management System Class

Example: Management System Basic Version (Difficulty ⭐⭐⭐)

▶ Example 1: Using STL Containers (Difficulty ⭐)

CPP

class ManagementSystem {
private:
	std::vector<Student*> students; // Student list (polymorphism)

public:
	// Add student
	void addStudent(Student* student) {
		students.push_back(student);
		std::cout << "Added successfully!" << std::endl;
	}
	
	// Find student
	Student* findStudent(const std::string& id) {
		for (auto s : students) {
			if (s->getId() == id) {
				return s;
			}
		}
		return nullptr;
	}
	
	// Display all students
	void displayAll() const {
		if (students.empty()) {
			std::cout << "No student information available" << std::endl;
			return;
		}
		
		for (auto s : students) {
			s->display();
			std::cout << "-------------------" << std::endl;
		}
	}
	
	// Destructor: free memory
	~ManagementSystem() {
		for (auto s : students) {
			delete s;
		}
	}
};

// Test code
int main() {
	ManagementSystem sys;
	
	// Add undergraduate
	sys.addStudent(new UndergraduateStudent("001", "Zhang San", 20, "Computer Science", 3));
	sys.addStudent(new GraduateStudent("002", "Li Si", 24, "Software Engineering", "Prof. Wang"));
	
	// Display all students
	sys.displayAll();
	
	return 0;
}

▶ Try it Yourself

Output:

TEXT 📖 Display only

Added successfully!
No student information available
-------------------

Run result:

TEXT 📖 Display only

Added successfully!
Added successfully!
Student ID: 001
Name: Zhang San
Age: 20
Major: Computer Science
Year: 3
Type: Undergraduate
-------------------
Student ID: 002
Name: Li Si
Age: 24
Major: Software Engineering
Advisor: Prof. Wang
Type: Graduate Student
-------------------

3. Complete Version Implementation

(1) 3.1 Adding More Features

Now, let's add more features to the system:

Feature	Implementation
Delete student	Delete by student ID
Modify info	Find by student ID, then modify
Grade management	Add a Grade class
Save to file	Use `ofstream` to write file
Load from file	Use `ifstream` to read file

(2) 3.2 Grade Class Design

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// Grade class
### ▶ Example 2: Object-Oriented Programming Demo (Difficulty ⭐)

class Grade {
private:
	std::string courseId; // Course ID
	std::string courseName; // Course name
	double score; // Score

public:
	Grade(const std::string& courseId, const std::string& courseName, double score)
	: courseId(courseId), courseName(courseName), score(score) {}
	
	void display() const {
		std::cout << courseName << ": " << score << " points" << std::endl;
	}
	
	double getScore() const { return score; }
};

// Add grade-related methods to the Student class
class Student {
	// ... other members ...
	std::vector<Grade> grades; // Grade list

public:
	void addGrade(const Grade& grade) {
		grades.push_back(grade);
	}
	
	void displayGrades() const {
		if (grades.empty()) {
			std::cout << "No grades available" << std::endl;
			return;
		}
		
		std::cout << name << "'s grades:" << std::endl;
		for (const auto& g : grades) {
			g.display();
		}
	}
	
	double getAverage() const {
		if (grades.empty()) return 0.0;
		
		double sum = 0;
		for (const auto& g : grades) {
			sum += g.getScore();
		}
		return sum / grades.size();
	}
};

(3) 3.3 File Operations

Save student information to file:

CPP

void saveToFile(const std::string& filename) {
	std::ofstream file(filename);
	if (!file) {
		std::cout << "Cannot open file" << std::endl;
		return;
	}
	
	for (auto s : students) {
		file << s->getId() << ","
			<< s->getName() << ","
			<< s->getAge() << std::endl;
	}
	
	file.close();
	std::cout << "Saved successfully!" << std::endl;
}

Load from file:

TEXT 📖 Display only

void loadFromFile(const std::string& filename) {
	std::ifstream file(filename);
	if (!file) {
		std::cout << "Cannot open file" << std::endl;
		return;
	}
	
	std::string id, name, ageStr;
	while (std::getline(file, id, ',')) {
		std::getline(file, name, ',');
		std::getline(file, ageStr);
		int age = std::stoi(ageStr);
		
		// Create student object (simplified; should distinguish undergraduate/graduate)
		students.push_back(new UndergraduateStudent(id, name, age, "Unknown", 1));
	}
	
	file.close();
	std::cout << "Loaded successfully!" << std::endl;
}

CPP

void showMenu() {
	std::cout << "\n===== Student Management System =====" << std::endl;
	std::cout << "1. Add student" << std::endl;
	std::cout << "2. Find student" << std::endl;
	std::cout << "3. Display all students" << std::endl;
	std::cout << "4. Enter grades" << std::endl;
	std::cout << "5. Save data" << std::endl;
	std::cout << "6. Load data" << std::endl;
	std::cout << "0. Exit" << std::endl;
	std::cout << "=====================================" << std::endl;
	std::cout << "Choose: ";
}

int main() {
	ManagementSystem sys;
	int choice;
	
	do {
		showMenu();
		std::cin >> choice;
		
		switch (choice) {
		case 1:
			// Add student
			break;
		case 2:
			// Find student
			break;
		case 3:
			sys.displayAll();
			break;
		case 0:
			std::cout << "Goodbye!" << std::endl;
			break;
		default:
			std::cout << "Invalid choice" << std::endl;
		}
	} while (choice != 0);
	
	return 0;
}

5. Project Extension Suggestions

(1) 5.1 Feature Extensions

Feature	Difficulty	Description
Grade Statistics	⭐⭐	Calculate averages, rankings
Data Validation	⭐⭐	Check input validity
Exception Handling	⭐⭐⭐	Use `try-catch` for errors
GUI	⭐⭐⭐⭐	Use Qt or wxWidgets
Database	⭐⭐⭐⭐	Use SQLite or MySQL

(2) 5.2 Code Optimization

Optimization	Description
Smart Pointers	Use `unique_ptr` for memory management
Const Correctness	Use `const` wherever possible
Exception Handling	Use `try-catch` for file errors
Operator Overloading	Overload `<<` for output

▶ Example 3: Simple Class Inheritance Hierarchy (Difficulty ⭐)

CPP

#include <iostream>
#include <string>

class Animal {
public:
    std::string name;
    Animal(const std::string& n) : name(n) {}
    virtual void speak() const = 0;
    virtual ~Animal() {}
};

class Dog : public Animal {
public:
    Dog(const std::string& n) : Animal(n) {}
    void speak() const override {
        std::cout << name << ": Woof!" << std::endl;
    }
};

class Cat : public Animal {
public:
    Cat(const std::string& n) : Animal(n) {}
    void speak() const override {
        std::cout << name << ": Meow!" << std::endl;
    }
};

int main() {
    Dog dog("Wangcai");
    Cat cat("Mimi");
    dog.speak();
    cat.speak();
    return 0;
}

▶ Try it Yourself

Output:

TEXT 📖 Display only

: Woof!
: Meow!

❓ FAQ

Q: Why use pointers to store students? A: To achieve polymorphism. Using vector<Student> would cause object slicing, so only base class methods could be called.

Q: What about memory leaks? A: Use smart pointers (unique_ptr) to automatically manage memory — no need for manual delete.

Q: How should I design the file format? A: You can use: - CSV format: simple, but limited functionality - JSON format: powerful, requires third-party library - Binary format: efficient, but not human-readable

Q How to handle Chinese characters?

A C++ has limited Chinese support. Suggestions: - Use wstring + wcout - Or use a third-party library (e.g., iconv) - Or only store pinyin/English

📖 Summary

Knowledge Point	Key Takeaway
Class Design	Base class + derived class, reflecting inheritance
Polymorphism	Use pointers/references to call virtual functions
File Operations	`ofstream` for writing, `ifstream` for reading
Memory Management	Destructor frees memory (or use smart pointers)
Menu Interface	`do-while` + `switch`

Study suggestions:

This project is a comprehensive exercise — make sure to type it out yourself
Implement basic features first, then gradually extend
When encountering problems, search for solutions first — develop problem-solving skills

📝 Exercises

Basic (Difficulty ⭐): Define a Book class (title, author, price), create 3 objects and output their properties.
Intermediate (Difficulty ⭐⭐): Implement an inheritance hierarchy: Shape (base class, pure virtual function area()) → Circle and Rectangle derived classes. Call area() polymorphically.
Challenge (Difficulty ⭐⭐⭐): Implement an "Observer pattern": Subject class maintains an Observer list, Observer is an abstract base class. When Subject state changes, notify all Observers.

This section covered the core concepts of OOP practice
With mastery, you can write related C++ programs

Phase 5 complete! Next: Phase 6 (Advanced STL)

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C++: Practice: OOP Comprehensive

1. Project Requirements Analysis

(1) 1.1 Functional Requirements

(2) 1.2 Class Design

2. Basic Version Implementation

(1) 2.1 Student Class Design

(2) 2.2 Management System Class

▶ Example 1: Using STL Containers (Difficulty ⭐)

3. Complete Version Implementation

(1) 3.1 Adding More Features

(2) 3.2 Grade Class Design

(3) 3.3 File Operations

4. Menu Interface Implementation

(1) 4.1 Main Menu

5. Project Extension Suggestions

(1) 5.1 Feature Extensions

(2) 5.2 Code Optimization

▶ Example 3: Simple Class Inheritance Hierarchy (Difficulty ⭐)

❓ FAQ

📖 Summary

📝 Exercises

C++: Practice: OOP Comprehensive

1. Project Requirements Analysis

(1) 1.1 Functional Requirements

(2) 1.2 Class Design

2. Basic Version Implementation

(1) 2.1 Student Class Design

(2) 2.2 Management System Class

▶ Example 1: Using STL Containers (Difficulty ⭐)

3. Complete Version Implementation

(1) 3.1 Adding More Features

(2) 3.2 Grade Class Design

(3) 3.3 File Operations

4. Menu Interface Implementation

(1) 4.1 Main Menu

5. Project Extension Suggestions

(1) 5.1 Feature Extensions

(2) 5.2 Code Optimization

▶ Example 3: Simple Class Inheritance Hierarchy (Difficulty ⭐)

❓ FAQ

📖 Summary

📝 Exercises

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