Data Structures & Arrays (Edexcel GCSE Computer Science)

What is a data structure?

• A data structure is a way of storing and organising data under one identifier so that it can be accessed and used efficiently

• There are a wide range of data structures in Computer Science, however, the exam only requires knowledge of:

  • Strings

  • Arrays

  • Records

Strings

What is a string?

• A string is a sequence of characters

• Speech marks can often identify something as a string

• Examples of strings include:

  • "Hello worlds"

  • "ABC"

  • "@#!%"

• It is important to choose the correct data type for a given situation to ensure accuracy and efficiency in the program

• Data types can be changed within a program, this is called casting

Records

What is a database?

• A Database is an organised collection of data

• It allows easy storage, retrieval, and management of information

• A database is useful when working with large amounts of data, databases are stored on secondary storage

• A database is often stored on remote servers so multiple users can access it at the same time, useful for online systems

• Data can be sorted and searched efficiently, making use of more advanced structures

• They are more secure than text files

• A database uses fields and records to organise how it stores data

What are fields & records?

• A field is one piece of information relating to one person, item or object

• A field is represented in a database by a column,

• A record is a collection of fields relating to one person, item or object

• A record is represented in a database by a row

Text files

• A text file is useful when working with small amounts of data, text files are stored on secondary storage and 'read' in to a program when being used

• They are used to store information when the application is closed

• Each entry is stored on a new line or separated with a special identifier, for example a comma (',')

• It can be difficult in text files to know where a record begins and ends

Arrays

• An array is useful when working with small amounts of data, arrays are stored in main memory (RAM)

• They are used to store information when the application is in use

• Can be more efficient and much faster to search than working with text files

1-Dimensional Arrays

What is an array?

• An array is an ordered, static set of elements in a fixed-size memory location

• An array can only store 1 data type

• A 1D array is a linear array

• Indexes start at 0, known as zero-indexed

Example in Python

Creating a one-dimensional array called ‘array’ which contains 5 integers.

• Create the array with the following syntax:
  array = [1, 2, 3, 4, 5]

• Access the individual elements of the array by using the following syntax:
  array[index]

• Modify the individual elements by assigning new values to specific indexes using the following syntax:
  array[index] = newValue

• Use the len function to determine the length of the array by using the following syntax:
  len(array)

• In the example the array has been iterated through to output each element within the array. A for loop has been used for this

2-Dimensional Arrays

What is a 2-dimensional array?

• A 2D array extends the concept on a 1D array by adding another dimension

• A 2D array can be visualised as a table with rows and columns

• When navigating through a 2D array you first have to go down the rows and then across the columns to find a position within the array

Example in Python