Indexed Variables

1
Indexed Variables

• Indexed variables ( arrays ) allow us to use many
  instances of a particular variable.
• This means we can specify algorithms which use
  many occurrences of identical variables easily.
• Consider an algorithm to record the number of
  occupants in a car which pass the university
  gates each day.
• Question Can you specify beforehand the number
  of cars that will pass by ?

2
Indexed Variables

• To solve this problem we introduce the concept of
  an index.
• The index points to a particular instance of a
  variable which can have many occurrences and is
  enclosed in square brackets after the variable
  name e.g.
• car1, car2, car3
• Whenever we require a new instance of a variable
  we augment the variable index.
• With this concept algorithms can store unknown
  amounts of related data.

3
Indexed Variables

• Example
• Algorithm to record number of car occupants. 0
  to stop
• index 1 Always ensure index is
  initialised to 1
• READ carindex Get value for car 1
• WHILE ( carindex ! 0 )
• index index 1 Now get ready
  for next car
• PRINT Enter number of occupants
• READ carindex
• ENDWHILE