Arrays in Turing

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Arrays in Turing
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Need for Arrays - Why?

• Currently every variable can contain only one
  data item at a time
• Currently previous piece of information stored
  will be replaced
• This is called destructive input

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Destructive Input

• Example
• var name string name "Fred Flintstone
• put "The name is ", name, "."
• name "Barney Rubble"
• put "The contents of name is ", name, "."
• name "George Jetson"
• put "The contents of name is now ", name, "."

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Arrays

• Provide a mechanism so that all contents can be
  stored under one variable
• No more destructive input
• Each element is accessed by the name of the
  variable and number of the content (subscript)

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Arrays Ordering

• Use arrays to organize data in a specific order
  (e.g. alphabetical/numerical)
• Sorting requires the items to be available in
  memory simultaneously for comparison

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Declaration of an Array

• The following are sample declarations

• var names array 1..4 of string4 strings
  accessed as names(1), names(2), names(3),
  names(4)
• var nums array 0..3 of int4 integers accessed
  as nums(0), nums(1), nums(2), nums(3)
• var realnums array 11..14 of real4 reals
  accessed by realnums(11), realnums(12),
  realnums(13), realnums(14)
• var status array 1..4 of boolean4 booleans
  accessed by status(1), status(2), status(3),
  status(4)

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Declaration of Arrays (Contd)

• Storing or accessing information to or from an
  array must include assigning to the variable name
  along with the subscript.

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Example Program Using an Array

• The following program
• declares an array of 10 integers
• randomly generates numbers between 1 and 100
• stores them into the array
• displays the numbers in the order in which they
  were generated

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Continued...

• The Program also
• displays the numbers in the reverse order (last
  to first generated)
• then calculates and displays the average of the
  10 numbers.
• outputs the contents of the fifth element in the
  array.

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The Program

• declaring the array of 10 integers var nums
  array 1..10 of int randomize
• randomly generating 10 numbers between 1 and
  100 and storing them in the array
• for i 1..10
• randint (nums (i), 1, 100)
• end for

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...

• output the list from the first to tenth
  element. As i
• increases from 1 to 10, it serves as the
  subscript to
• identify which array element we want. On the
  first
• iteration of the counted loop, i has a value of
  1 so
• nums(i) is accessing the contents of num(1),
  etc.
• put "The list of numbers between 1 and 100 that
  has been ..
• put generated is
• for i 1..10
• put nums(i)
• end for