Arrays

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Arrays
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Objectives

• Understand how arrays are used
• Understand how arrays occupy computer memory
• Manipulate an array to replace nested decisions
• Declare and initialize an array
• Understand the difference between run-time and
  compile-time arrays
• Load array values from a file

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Objectives (cont)

• Search for an array for an exact match
• Use parallel arrays
• Force subscripts to remain within array bounds
• Improve search efficiency by using an early exit
• Search an array for a range match

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Understanding Arrays

• Arrayseries or list of variables in computer
  memory, all of which have the same name but are
  differentiated with special numbers called
  subscripts
• Subscriptsnumber that indicates the position of
  a particular item within an array

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How Array Occupy Computer Memory

• Elementeach separate array variable
• Size of the Arraynumber of elements an array
  will hold
• All array elements have the same group name, but
  each individual element also has a unique
  subscript indicating how far away it is from the
  first element

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Subscript

• Variable could be used as a subscript as long as
  it is
• Numeric with no decimal places
• Initialized by 1
• Incremented by 1 each time the logic passed
  through the loop

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Terms

• Initialization looploop structure that provides
  initial values for every element in any array
• Run-time array or execution-time arrayarray that
  receives its final values during an actual run,
  or execution, of a program
• Compile-time arraysone whose final desired
  values are fixed at the beginning of the program
• Hard codedexplicitly assigned to the array
  elements

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Using Parallel Arrays

• Parallel arrayseach element in one array is
  associated with the element in the same relative
  position in the other array

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Remaining Within Array Bounds

• Out of Boundsusing a subscript that is not
  within the range of acceptable subscripts
• Ordering a wrong item number is a frequent error

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Early Exit

• Leaving a loop as soon as a match is found
• Improves the programs efficiency
• The larger the array, the more beneficial it
  becomes to exit the searching loop as soon as you
  find what youre looking for

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Range Match

• Range of valuesany set of contiguous vales

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Summary

• An array is a series or list of variables in
  computer memory, all of which have the same name
  but are differentiated with special numbers
  called subscripts
• When you declare an array, you declare a
  programming structure that contains multiple
  elements
• You often can use a variable as a subscript to an
  array, replacing multiple nested decisions
• You can declare and initialize all of the
  elements in an array using a single statement
  that provides a type, a name, and a quantity of
  elements for the array
• An array whose values are determined during the
  execution of a program is a run-time array, or
  execution-time array
• You can load an array from a file

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Summary (cont)

• Searching through an array to find a value you
  need involves initializing a subscript, using a
  loop to test each array element, and setting a
  flag when a match if found
• In parallel arrays, each element in one array is
  associated with the element in the same relative
  position in the other array
• Your programs should ensure that subscript values
  do not go out of bounds, that is take on a value
  out of the range of legal subscripts
• When you need to compare a value to a range of
  values in an array, you can store either the
  low-or high-end value of each range for comparison