Revise Data Types and Records for Cambridge 9618 (10.1)

Think of primitive data types as the atoms of information in your program. They are the simplest, most fundamental units provided by a programming language. Every piece of data, from a user's age to the price of an item, must be assigned a type so the computer knows how to store it and what operations are permissible.

Often, we need to handle data that is more complex than a single number or string. A 'student', for example, has a name, an ID number, and several grades. Instead of juggling many separate variables (StudentName, StudentID, StudentGrade), we can group them into a single, logical unit called a record. A record is a composite data type you define yourself.

TYPE TStudent = RECORD Name : STRING StudentID : INTEGER DateOfBirth : DATE IsFeePaid : BOOLEAN ENDRECORD

In this Cambridge-style pseudocode, we use the TYPE keyword to define a new data type called TStudent. This new type acts as a template, containing fields like Name and StudentID, each with its own primitive data type. The $T$ prefix is a common convention to denote a 'Type', which improves code readability.

Defining a record type with TYPE is like creating a blueprint. To actually store data, you need to build an object from that blueprint. This is done by declaring a variable of your new record type using the DECLARE keyword. Once you have a record variable, you can access its individual fields using dot notation (.).

// To declare a single record variable DECLARE MyBook : TBook

// To assign a value to a field MyBook.Title <- "The Pragmatic Programmer" MyBook.Price <- 25.50

// To access and output a field's value OUTPUT MyBook.Author