src/main/java/Main.java

@@ -70,7 +70,12 @@ public class Main {
         boolean success;
         switch (choice) {
             case 1:
-                //TODO
+                success = school.registerStudent(username, password);
+                if(success){
+                    System.out.println(" Student registered successfully!");
+                }else {
+                    System.out.println(" Username already exists!");
+                }
                 break;
             case 2:
                 success = school.registerTeacher(username, password);
@@ -103,7 +108,12 @@ public class Main {
 
         switch (choice) {
             case 1:
-                //TODO
+                Student student = school.loginStudent(username , password);
+                if(student != null){
+                    studentMenu(student);
+                }else{
+                    System.out.println(" Invalid username or password!");
+                }
                 break;
             case 2:
                 Teacher teacher = school.loginTeacher(username, password);
@@ -153,7 +163,19 @@ public class Main {
     }
 
     private static void enrollInCourse(Student student) {
-       //TODO
+        System.out.print(school.getAllCoursesDisplay());
+        System.out.print("\n Enter Course ID to enroll: ");
+        int courseId = getIntInput();
+        Course course = school.findCourseById(courseId);
+        if(course == null){
+            System.out.println(" Course not found! Please enter a valid ID.");
+            return;
+        }
+        if(student.enrolledCourses(course)){
+            System.out.println("Successfully enrolled in" + course.getName());
+        }else{
+            System.out.println(" You are already enrolled in this course!");
+        }
     }
 
     // ==================== TEACHER MENU ====================

src/main/java/models/Student.java

@@ -11,5 +11,28 @@ public class Student extends User {
         this.enrolledCourses = new ArrayList<>();
     }
 
-  //TODO
+    public boolean enrolledCourses(Course course){
+        if(enrolledCourses.contains(course)){
+            return false;
+        }
+        enrolledCourses.add(course);
+        course.addStudent(this);
+        return true;
+    }
+
+    public List <Course> getEnrolledCourses(){
+        return enrolledCourses;
+    }
+
+    public String getMyCoursesDisplay(){
+        if(enrolledCourses.isEmpty()){
+            return " You are not enrolled in any course yet.";
+        }else{
+            StringBuilder sb = new StringBuilder("\n My Course: \n");
+            for (int i = 0; i < enrolledCourses.size(); i++) {
+                sb.append(" ").append(i+1).append(". ").append(enrolledCourses.get(i)).append("\n");
+            }
+            return sb.toString();
+        }
+    }
 }

src/main/java/models/Teacher.java

@@ -32,22 +32,26 @@ public class Teacher extends User {
         return myCourses;
     }
 
-    public void showMyCourses() {
+    public String getMyCoursesDisplay() {
         if (myCourses.isEmpty()) {
-            System.out.println(" You don't teach any course yet.");
+            return " You don't teach any course yet.";
         } else {
-            System.out.println("\n My Courses:");
+            StringBuilder sb = new StringBuilder("\n My Courses:\n");
             for (int i = 0; i < myCourses.size(); i++) {
-                System.out.println("  " + (i+1) + ". " + myCourses.get(i));
+                sb.append("  ").append(i+1).append(". ").append(myCourses.get(i)).append("\n");
             }
+            return sb.toString();
         }
     }
 
-    public void showStudentsInCourse(Course course) {
-        if (!myCourses.contains(course)) {
-            System.out.println(" You don't teach this course!");
-            return;
+    public boolean checkCourseOwnership(Course course) {
+        return myCourses.contains(course);
     }
-        course.showStudents();
+
+    public String getStudentsDisplayForCourse(Course course) {
+        if (!myCourses.contains(course)) {
+            return "You don't teach this course!";
+        }
+        return course.getStudentsDisplay();
     }
 }

src/main/java/services/SchoolSystem.java

@@ -16,7 +16,28 @@ public class SchoolSystem {
     }
 
     // ========== Student Management ==========
-   //TODO
+    public boolean registerStudent(String username , String password){
+        if(findStudent(username) != null){
+            return false;
+        }
+        students.add(new Student(username , password));
+        return true;
+    }
+
+    public Student loginStudent(String username, String password) {
+        Student student  = findStudent(username);
+        if (student != null && student.checkPassword(password)) {
+            return student;
+        }
+        return null;
+    }
+
+    private Student findStudent(String username) {
+        for (Student s : students) {
+            if (s.getUsername().equals(username)) return s;
+        }
+        return null;
+    }
 
     // ========== Teacher Management ==========
     public boolean registerTeacher(String username, String password) {
@@ -44,12 +65,21 @@ public class SchoolSystem {
 
     // ========== Course Management ==========
     public boolean addCourseToSystem(String courseName) {
-        //TODO
+        for (Course c : allCourses){
+            if(c.getName().equals(courseName)){
+                return false;
+            }
+        }
+        allCourses.add(new Course(courseName));
         return true;
     }
 
     public Course findCourseById(int id) {
-       //TODO
+        for(Course c : allCourses){
+            if (c.getId() == id){
+                return c;
+            }
+        }
         return null;
     }