adding student program

lectures/25_inheritance/README.md

@@ -133,7 +133,7 @@ If no access specifier is provided:
 
 private members of the base class are never accessible directly in the derived class, regardless of the inheritance type.
 
-### 25.5 Constructors and Destructors
+## 25.5 Constructors and Destructors
 
 - Constructor Invocation: When a derived class object is created, the base class constructor is invoked first, followed by the derived class constructor.
 
@@ -156,3 +156,19 @@ public:
     }
 };
 ```
+
+## 25.6 Example Programs:
+
+We develop this student_test.cpp program.
+
+### version 1
+
+[student_test1.cpp](student_test1.cpp) In this version, there is only one class: class Human
+
+### version 2
+
+[student_test2.cpp](student_test2.cpp) In this version, there is the base class - Human, and the child class - Student, but the child class doesn't have its own member variables, and its only member function is the constructor.
+
+### version 3
+
+[student_test3.cpp](student_test3.cpp) In this version, the child class has its own member functions introduce() and sleep(); and because these functions need to access the parent class's member variables, so we changed the member variables from private to protected.

lectures/25_inheritance/students/student_test1.cpp

@@ -0,0 +1,35 @@
+#include <iostream>
+#include <string>
+
+class Human {
+private:
+    std::string name;
+    int age;
+    int sleep_hours;
+
+public:
+    Human(std::string n, int a, int s) : name(n), age(a), sleep_hours(s) {}
+
+    void introduce() {
+        std::cout << "Hello, I am " << name << ", and I am " << age << " years old.\n";
+    }
+
+    void sleep() {
+        std::cout << name << " is " << age << " years old who sleeps " << sleep_hours << " hours a night.\n";
+    }
+};
+
+int main() {
+    // Creating instances of each class with member variables
+    Human h("Alice", 30, 8);
+
+    // Introducing Humans
+    std::cout << "--- Human introducing ---\n";
+    h.introduce();  // Output: Hello, I am Alice, and I am 30 years old.
+    
+    // Showing sleep behavior
+    std::cout << "--- Human sleep ---\n";
+    h.sleep();  // Output: Alice is 30 years old and sleeps 8 hours a night.
+
+    return 0;
+}

lectures/25_inheritance/students/student_test2.cpp

@@ -0,0 +1,48 @@
+#include <iostream>
+#include <string>
+
+class Human {
+private:
+    std::string name;
+    int age;
+    int sleep_hours;
+
+public:
+    Human(std::string n, int a, int s) : name(n), age(a), sleep_hours(s) {}
+
+    void introduce() {
+        std::cout << "Hello, I am " << name << ", and I am " << age << " years old.\n";
+    }
+
+    void sleep() {
+        std::cout << name << " is " << age << " years old who sleeps " << sleep_hours << " hours a night.\n";
+    }
+};
+
+class Student : public Human {
+public:
+    Student(std::string n, int a, int s) : Human(n, a, s) {}
+};
+
+int main() {
+    // Creating instances of each class with member variables
+    Human h("Alice", 30, 8);
+    Student s("Bob", 20, 5);
+
+    // Introducing Humans
+    std::cout << "--- Human introducing ---\n";
+    h.introduce();  // Output: Hello, I am Alice, and I am 30 years old.
+    
+    std::cout << "--- Student introducing ---\n";
+    s.introduce();  // Output: I am a student. My name is Bob, and I am 20 years old.
+
+    // Showing sleep behavior
+    std::cout << "--- Human sleep ---\n";
+    h.sleep();  // Output: Alice is 30 years old and sleeps 8 hours a night.
+
+    std::cout << "--- Student sleep ---\n";
+    s.sleep();  // Output: Bob is a student, and they sleep 5 hours a night.
+
+    return 0;
+}
+

lectures/25_inheritance/students/student_test3.cpp

@@ -0,0 +1,57 @@
+#include <iostream>
+#include <string>
+
+class Human {
+// change this to protect so that these variables can be accessed by the derived class.
+protected:
+    std::string name;
+    int age;
+    int sleep_hours;
+
+public:
+    Human(std::string n, int a, int s) : name(n), age(a), sleep_hours(s) {}
+
+    void introduce() {
+        std::cout << "Hello, I am " << name << ", and I am " << age << " years old.\n";
+    }
+
+    void sleep() {
+        std::cout << name << " is " << age << " years old who sleeps " << sleep_hours << " hours a night.\n";
+    }
+};
+
+class Student : public Human {
+public:
+    Student(std::string n, int a, int s) : Human(n, a, s) {}
+    
+    void introduce() {
+        std::cout << "Hello, I am " << name << ", and I am " << age << " years old. I’m majoring in 'How did I get here?' with a minor in 'It sounded easier when I signed up.'\n";
+    }
+
+    void sleep() {
+        std::cout << name << " is a college student who sleeps " << sleep_hours << " hours a night, and sleep 2 hours during boring lectures.\n";
+    }
+};
+
+int main() {
+    // Creating instances of each class with member variables
+    Human h("Alice", 30, 8);
+    Student s("Bob", 20, 5);
+
+    // Introducing Humans
+    std::cout << "--- Human introducing ---\n";
+    h.introduce();  // Output: Hello, I am Alice, and I am 30 years old.
+    
+    std::cout << "--- Student introducing ---\n";
+    s.introduce();  // Output: I am a student. My name is Bob, and I am 20 years old.
+
+    // Showing sleep behavior
+    std::cout << "--- Human sleep ---\n";
+    h.sleep();  // Output: Alice is 30 years old and sleeps 8 hours a night.
+
+    std::cout << "--- Student sleep ---\n";
+    s.sleep();  // Output: Bob is a student, and they sleep 5 hours a night.
+
+    return 0;
+}
+