User-Defined Data Types (UDTs)

What is meant by a user-defined data type? [2 marks]

1. A data type that is not built-in/primitive to the language [1]

2. Created and defined by the programmer to suit a specific problem [1].

State the difference between a non-composite (primitive user-defined) and a composite data type. [2 marks]

Non-composite: Does not involve a reference to any other data type (e.g., Enumerated, Pointer) [1].

Composite: Is constructed from/refers to multiple other data types (e.g., Record, Set, Class) [1].

Write pseudocode to declare an enumerated data type. [2 marks]

TYPE <TypeName> = (<Value1>, <Value2>, <Value3>, ...)

Example: ⁠TYPE DayOfWeek = (Monday, Tuesday, Wednesday, Thursday, Friday)⁠ [2]

Identify two characteristics/features of an enumerated data type. [2 marks]

1. The values are user-defined identifiers (constants) [1].

2. The data type is ordered/sequential (each value has an ordinal position/index) [1].

3. It is a non-composite data type [1].

Write pseudocode to declare a composite data type (Record/Class) containing multiple fields of different types, including a previously declared enumerated type. [4–5 marks]

TYPE <RecordName>

DECLARE <Field1> : <DataType1>

DECLARE <Field2> : <EnumTypeName>

DECLARE <Field3> : ARRAY[1..N] OF <DataType3>

ENDTYPE

Write pseudocode to declare a pointer data type. [2 marks]

TYPE <PointerTypeName> = ^<BaseTypeName>

Example: ⁠TYPE PtrNode = ^Node⁠ [2]

State advantages of using user-defined data types in programming. [2–3 marks]

1. Improves readability and maintainability of the code [1].

2. Allows logical grouping of related data items [1].

3. Provides built-in type safety/validation (especially enumerated types restrict variables to legal values only) [1].

Define a non-composite data type and give two examples.

A user-defined data type that does not involve a reference to another data type.

Examples: Enumerated, Pointer.

Define a composite data type and give three examples.

A user-defined data type that refers to / is constructed from one or more other data types.

Examples: Record, Set, Class/Object.