Arrays, Tuples and Records

• Data structure


  A way of organizing and storing data in a computer so that it can be used efficiently
• Elementary data types


  • integer
  • real
  • Boolean
  • char
• Structured data types


  • string
  • array
  • record
• Array


  A finite, ordered set of elements of the same type
• An array has a specific number of elements and the elements are ordered (first, second, third, etc.)
• Example array


  • myArray[51, 72, 35, 37, 0, 31]
• x = myArray[2] assigns 35 to x
• The RSPB organises a Big Garden Birdwatch to involve the public in counting the number of birds of different types they see in their gardens on a particular weekend
• During 30-31 January 2016, more than 8 million birds were counted and reported
• The scientists add all the sightings together, and once the data has been analysed they can discover trends and understand how different birds and other wildlife are faring
• Example array of bird names

  • birdName["robin", "blackbird", "pigeon", "magpie", "bluetit", "thrush", "wren", "starling"]
• birdName[2] = "pigeon"
• numSpecies = len(birdName) assigns 8 to numSpecies
• 1. dimensional arrays


  An array can have two or more dimensions. A two-dimension array is like a spreadsheet.
• 1. dimensional array


  • numbers
  • 3 rows, 4 columns
• Elements in the array

  Referred to by their row and column number, e.g. numbers[1,3]
• 1. dimensional array "numbers"


  • Row 0: 2, Column 1, Column 2, Column 3
  • Row 1: 5, 6
  • Row 2: 9, 10, 11, 12
• Value of numbers[2,3]


  12
• Pseudocode algorithm to print quarterly sales

  1. For each of 3 sales staff (Anna, Bob, Carol)

  2. Print staff name

  3. For each quarter (0 to 3)

  4. Print quarter number and sales figure

  5. Calculate annual sales
• The staff names are in a 1-dimensional array "staff"
• The quarterly sales figures are in a 2-dimensional array "quartersales"
• Arrays may have more than two dimensions. An n-dimensional array is a set of elements of the same type, indexed by n integers.
• 1. dimensional array


  • x[4,5,2]
• Tuple


  An ordered set of values, which could be elements of any type such as strings, integers or numbers, or even graphic images, sound files or arrays
• Tuple


  • Unlike arrays, the elements do not have to be of the same type
  • A tuple, like a string, is immutable, which means that its elements cannot be changed, and you cannot dynamically add elements to or delete elements from a tuple
• Tuple


  • pupil ("John", 78, "a")
• Referring to individual elements of a tuple

  name pupil(0)
• The statement pupil[0] is invalid
• Record


  A record contains a number of fields, each holding one item of data
• Record structure


  • ID
  • Firstname
  • Surname
  • DateOfBirth
  • Class
• User-defined data type


  • studentType
  • integer ID
  • string firstname
  • string surname
  • date dateOfBirth
  • string class
• Accessing fields in a record

  student.surname