complete the RegistrationSystem file

.idea/misc.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
-  <component name="ProjectRootManager" version="2" project-jdk-name="25" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" project-jdk-name="21" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
   </component>
 </project>

src/CourseRegistrationStarter/RegistrationSystem.java

@@ -9,16 +9,21 @@ public class RegistrationSystem {
     }
 
     public void addCourseToSystem(Course c) {
-        // TODO: Add the course to the system
+        courses.add(c);
     }
 
     public Course findCourseByCode(String code) {
-        // TODO: Search for a course by course code
-        // Return the matching course if found, otherwise return null
+        for (Course c : courses) {
+            if (c.getCourseCode().equals(code)) {
+                return c;
+            }
+        }
         return null;
     }
 
     public void showAllCourses() {
-        // TODO: Print all courses in the system
+        for (Course c : courses) {
+            System.out.println(c);
+        }
     }
 }