A number of students have struggled with the data structures for this project, so this page will give a few hints.

Figure 11.23 in the book shows a cross-reference tree. Here is a corrected version of that figure:

The registration data will look similar--each student is a node in the tree; that student's courses are contained in a singly-linked list. The student node's data field will be a record with the following fields:

• student ID (positive, range 1111..9999) -- the student key
• student name (10-character fixed-length string, e.g., "Mary Smith")
• header block for a linked list that will store the courses for which this student has registered

Suppose student 1234, Lara Croft, is registered for two courses, 22 and 54. Lara's tree node will look like this:
 

Here are possible declarations of some of the data structures:

SUBTYPE CRNRange IS Positive RANGE 11..99;
PACKAGE RegistrationLists IS NEW Singly_Linked_Lists_Generic(...);

SUBTYPE StudentIDRange IS Positive RANGE 1111..9999;
SUBTYPE StudentName IS String(1..10);

TYPE StudentInfo IS RECORD
  ID: StudentIDRange := 1111;
  Name: StudentName := "zzzzzzzzzz";
  Courses: RegistrationLists.List;
END RECORD;

TYPE TreeNode;
TYPE Tree IS ACCESS TreeNode;
TYPE TreeNode IS RECORD
  Info: StudentInfo;
  Left: Tree;
  Right: Tree;
END RECORD;