Array Basics (Cambridge International A-Level Computer Science)

Arrays

What is an array?

• An array is an ordered, static set of elements
• Can only store 1 data type
• The position of each element in an array is identified using the array's index
• The array's first element is the lower bound (LB)
• The array's last element is the upper bound (UB)
• The lower bound of an array is typically 0 or 1 depending on the language being used
• An array can be one-dimensional or multi-dimensional

One-dimensional (1D) arrays

• A 1D array is a linear array

• To declare a 1D array in pseudocode you must include the lower bound, upper bound and data types:

• In this example a 1D array of five elements each containing single character can be declared as:

• An example complete program could be:

• The array is declared with indices from 0 to 4

• Each element stores a single character using the CHAR data type

• The loop outputs each letter in order

Two-dimensional (2D) arrays

• A 2D array can be visualised as a table
• 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

• In 2D arrays the following must be declared:

  • Lower bound for rows (LBR) & upper bound for rows (UBR)
  • Lower bound for columns (LBC) & upper bound for columns (UBC)

• In this example a 2D array can be declared as:

• An example complete program could be:

• ARRAY[0:2, 0:4] creates 3 rows and 5 columns

• First index is the row, second is the column: Grid[Row, Column]

• All elements are of type CHAR

Worked Example A program reads data from a file and searches for specific data.

The main program needs to read 25 integer data items from the text file Data.txt into a local 1D array, DataArray

Write program code to declare the local array DataArray [1]

Final answer: Answer

• 1D array with name DataArray (with 25 elements of type Integer) [1 mark]

Java

public static Integer[] DataArray = new Integer[25];

VB.NET

Dim DataArray(24) As Integer

Python

DataArray = [] #25 elements Integer