the aim being to simplify access and processing of the data.
When designing data structures for particular problems it is important to carefully consider the nature of the processing that will be required.
Well-designed data structures can significantly reduce the complexity of the processing required.
Conversely poor or inappropriate data structures can greatly increase the processing required and reduce the software’s performance.
In the preliminary course we introduce three data structures: arrays, records and files.
These three structures can be combined in various ways to suit the data and processing requirements of individual problems.
One-dimensional array
Arrays are used to store multiple data items where each data item is of the same data type.
Each element within the array has a unique index that is used to access the data contained within the element.
Structures similar to arrays are used extensively in non-computing applications.
For example, post office boxes (PO boxes).
PO boxes are numbered sequentially within each post office.
These numbers are used as indexes when locating a particular PO box.
Each PO box is a storage container for mail.
The mail (data items) will change within a particular storage container but the container and its index remain constant.
The ordered and sequential nature of the PO box numbers together with the boxes physical arrangement simplifies the sorting and distribution of mail.
In the case of PO boxes there is a single index, the PO box number.
In the HSC course we examine arrays that use multiple indexes, called multidimensional arrays. At this stage we restrict our discussion to arrays with single indexes, one-dimensional arrays.
Simple One Dimensional Array
Record
A data structure containing data items that are related but not necessarily of the same data type is called a record.
Records are used extensively for database applications.
Generally individual records contain all the information about a particular entity (or individual) within the database.
For example, an address book contains details of individual people. Each person is an entity within the address book and has their own record.
Before a record structure can be used as a data type, its fields must be named and each assigned a data type. The record structure then becomes a user-defined data type that can be used in the same way as the predefined included data types.
Sequential files
Files are used to permanently store data on secondary storage devices.
Data can be written to a file or read from a file.
Different types of access to files suit different requirements.
Sequential files can only be accessed from start to finish.
That is, to read or write to the middle of a sequential file requires accessing all the data prior to that position in the file.
It is not possible to jump directly to a particular data item.
Sequential files are continuous streams of data (usually characters).
The structure of the data is not coded as part of the file.
If the data within the file has some structure then the software must understand this structure; the file itself does not contain this information.
This structure can be defined using a RECORD datatype.
Many languages contain statements that allow data to be written and read a single character at a time, a data item at a time, record at a time or a line at a time.
Separators are inserted by the programming language to separate data items e.g. commas or tabs.
Carriage returns and/or line feed characters are added after each line.
