One Dimensional Arrays

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One Dimensional Arrays

• Chapter 11

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"All students to receive arrays!" reports Dr.
Austin.
scores 85 79 92 57 68 80 . . .
0 1 2 3 4 5 98 99
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Design Problem

• Consider a program to calculate class average

?
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Add to Design Problem

• Now your client says, I need to ALSO calculate
  and display deviations from the average

Describe why this will or will NOT work
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Possible Solutions
?

• Enter in the scores again
• Use 100 separate variables
• and cout and cin commands
• Read (then re-read) from a file
• The real answer

?
?
Use arrays!!
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Simple vs Structured Data Types

• Simple data type gt data element contains a
  single value
• Structured data type gt a data element contains a
  collection of data values

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Arrays

• Arrays are Structured Data Types
• They have a means of accessing individual
  components
• Values can be retrieved from and stored in the
  structure

scores 85 79 92 57 68 80
0 1 2 3 4 5
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One Dimensional Array

• Structured collection of components
• All of the same type
• Structure given a single name
• Individual elements accessed by index indicating
  relative position in collection
• Type of elements stored in an array can be just
  about anything
• Index of an array must be an integer

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Use of Array for Our Problem

• Store elements in array as read in
• Go back and access for deviations

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Declaring Arrays

• Syntax Data_type Array_name constant
• Note declaration from our example

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Declaring Arrays

• Example specifies an array
• each element is an integer
• there is space for 100 elements
• the are numbered 0 through 99

scores 85 79 92 57 68 80 . . .
0 1 2 3 4 5 98 99
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Accessing Individual Components

• Use the name of the array
• Followed by an integer expression inside the
  square brackets

scores 85 79 92 57 68 80 . . .
0 1 2 3 4 5 98 99
Index can be- constant- variable-
expressionMUST be an integer
max scores0for (x 0 x lt 100 x) if
(scoresx gt max) max scoresx
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Out of Bounds Index

• What happens if
• C does NOT check for index out of range
• Possible to walk off into far reaches of memory
  -- clobbers ...
• other variable locations
• .exe code
• the operating system (??)

float f_list 50 f_list 100 123.456
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Initializing Arrays in Declarations

• Possible to declare the size initialize
• Possible to omit size at declaration
• Compiler figures out size of array

int results 5 14, 6, 23, 8, 12
float prices 2.41, 85.06, 19.95, 3.91
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Aggregate Operations

• Defn gt an operation on the data structure as a
  whole
• as opposed to operation on a SINGLE element
  within the structure
• Example
• would be nice to read in a WHOLE array

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Lack of Aggregate Operations

• Would be nice but . . . C does NOT have . .
  .
• Assignment operator for whole array
• Arithmetic operations for whole array (think
  matrix)
• Comparisons for arrays (not even )
• Return of an array type by a function

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How to Accomplish Aggregate Operations?

• Most such tasks (assignment, read, write) can be
  performed some other way
• CS II course will write classes to provide
  these functions
• Otherwise
• these operations must be performed by the
  programmer
• element by element in a loop

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Arrays as Parameters

• This is one task that CAN be done to the WHOLE
  array
• C always passes arrays by reference

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Arrays as Parameters

• The name of the array is a pointer constant
• The address of the array is passed to the
  function
• Size of thearray alsopassed tocontrol loop

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Arrays as Parameters

• Note the empty brackets in parameter list
• A number can be placed here but it will beignored

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Sub-array Processing

• Note we specified an array size of 100
• but we dont anticipate that many scores
• Array always declared larger than needed
• Must keep track of how many have been used
• this is our limit when doing other things to the
  array

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Design Problem

• Consider the task of keeping track of data about
  parts for manufacture
• part number, description, qty needed, unit price

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Design Problem

• Use Parallel arrays
• One array each for part num, descrip, qty, price
• nth item in any one of the arrays associated with
  same nth item of all the arrays

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Testing and Debugging Hints

• Range of legal index values is 0 to array_size -
  1
• Individual elements of the array are of the
  component type
• No aggregate operations in arrays
• you must write the code to do this
• If array parameter is incoming, specify formal
  parameter as const
• prevents function from modifying

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Testing and Debugging Hints

• Omitting array size in declaration
• when array declared formal parameter
• when array initialized at declaration
• Dont pass component when function expects entire
  array
• Declare array size as max ever needed
• process only part of array which is used
• Pass array name and length to functions which
  process array or sub array