Chapter 13.1: User-Defined Data Types

Answer:

• Example: Enumerated or Pointer
• A built-in data type has a pre-defined range of possible values
• Built-in types are used by any program universally
• User-defined types: the programmer defines a specific range unique to that program
• User-defined types are tailored to the specific requirements of the program

Additional points for deeper understanding: User-defined types improve code readability and make programs easier to debug by restricting values to meaningful options.

Answer:

• A record is a composite data type
• It contains a fixed number of components/fields
• Components can be of different data types
• It groups related data together in one structure
• Each field has a name and specific data type

Answer:

• Related data can be referenced with one construct
• Very flexible because different types allowed for the components
• A value for a component can be accessed individually using dot notation
• Makes code easier to read and maintain
• Can create arrays of records for multiple items

Answer:

TYPE Animal
    DECLARE AnimalName : STRING
    DECLARE AnimalAge : INTEGER
    DECLARE NumberInZoo : INTEGER
    DECLARE LocationInZoo : STRING
ENDTYPE

Additional notes: Type name should start with T convention (e.g., TAnimal), and field names should be descriptive. Each field must have an appropriate data type.

Answer:

TYPE TDirection = (North, East, South, West)

DECLARE CurrentDirection : TDirection
CurrentDirection ← North

// Can also use ordinal operations
CurrentDirection ← CurrentDirection + 1  // Now East

Additional points: Values are ordinal, so you can use +1, -1 operations. Values are NOT strings and do not use quotation marks.

Answer:

• A pointer is a non-composite data type that stores a memory address
• It references a memory location where data is stored
• Dereferencing means accessing the value at the memory address
• Use ^ symbol to dereference (e.g., MyPointer^)

TYPE TIntPointer = ^INTEGER
DECLARE ptr : TIntPointer
DECLARE num : INTEGER
num ← 100
ptr ← @num        // ptr now holds address of num
OUTPUT ptr^       // Dereference: outputs 100

Answer:

• Non-composite: Defined without referencing another data type; contains only one data item
• Examples: Enumerated types, Pointer types
• Composite: References other data types in its definition; contains multiple data items
• Examples: Records, Sets, Classes

Key distinction: A record is composite because it references STRING, INTEGER, etc. in its definition. An enumerated type is non-composite because it only defines a list of values, not referencing any other type.

Answer:

• Sets contain unordered elements
• No duplicate values are allowed
• Supports mathematical operations: union, intersection, difference
• Can test for membership (ISIN)
• Example use: Storing vowels, colours, user IDs where uniqueness is required

TYPE SVowel = SET OF CHAR
DEFINE vowels ('a', 'e', 'i', 'o', 'u') : SVowel
IF 'e' ISIN vowels THEN
    OUTPUT "It's a vowel"
ENDIF

Answer:

TYPE TStudent
    DECLARE Name : STRING
    DECLARE Age : INTEGER
    DECLARE Grade : STRING
ENDTYPE

DECLARE Students : ARRAY[1:50] OF TStudent

// Assign values to first student
Students[1].Name ← "Alice"
Students[1].Age ← 17
Students[1].Grade ← "A"

// Output first student's name
OUTPUT Students[1].Name

Key points: Use dot notation with array index to access fields. The record type groups related data together efficiently.

Answer:

• No suitable built-in type exists: When data requires a unique structure (e.g., a 'Student' type with multiple attributes)
• Specific behaviors needed: For operations not available in standard types (e.g., restricting input to predefined values using enumerated types)
• Real-world modeling: To represent real-world entities accurately (e.g., Employee record with name, salary, department)
• Code organization: Makes programs easier to code, read, and debug
• Reusability: Once defined, the type can be used throughout the program

Answer:

• Both are composite data types that group related data
• Records contain only data fields
• Classes contain data fields AND methods (procedures/functions)
• Classes define a blueprint for creating objects with behavior
• Records are simpler structures just for organizing data

Example: A Student record has Name, Age, Grade. A Student CLASS would also have methods like CalculateGPA() or Promote().