an object-oriented approach to programming logic and design chapter 7 arrays

An Object-Oriented Approach to An Object-Oriented Approach to

Programming Logic and DesignProgramming Logic and Design

Chapter 7Arrays

An Object-Oriented Approach to Programming Logic and Design 2

ObjectivesObjectives

• Understand arrays and how they occupy computer memory

• Manipulate an array to replace nested decisions

• Declare and initialize an array• Understand the difference between initialized

and uninitialized arrays• Load array values from a file


Objectives (continued)Objectives (continued)

• Search an array for an exact match• Use a constant to store an array size• Search an array for a range match


Understanding Arrays Understanding Arrays and How They Occupy Memoryand How They Occupy Memory

• Array: a series or list of variables in memory that have the same name and type but different subscripts (or indexes)

• Subscript (or index): a number that indicates the position of an item within the array

Example: mailboxes in an apartment building – all have the same street address (name), but each has a different apartment number (subscript)


How Arrays Occupy How Arrays Occupy Computer MemoryComputer Memory

• Element: one item in the array; has a common name and a unique subscript, and stores a value

• Size of the array: the number of elements in the array

• Subscripts start at 0 • An array’s elements are stored contiguously in

memory


How Arrays Occupy How Arrays Occupy Computer Memory (continued)Computer Memory (continued)


Manipulating an Array to Replace Manipulating an Array to Replace Nested DecisionsNested Decisions


Manipulating an Array to Replace Manipulating an Array to Replace Nested Decisions (continued)Nested Decisions (continued)



• Using an array can greatly reduce the amount of code required

• Subscript can be represented by a constant or a variable

• Using a variable for the subscript allows the use of a loop to cycle through all elements in an array



• Because the action taken was the same for each element of the array, the code can be significantly shortened

• Using a variable for the subscript replaces the need for decision structures in this example



• Subscript – Can have any legal name

– Must be numeric with no decimal places

– Must be initialized to 0

– Must be incremented by 1 each time the logic passes through a loop

• Arrays make code easier to read


Array Declaration and InitializationArray Declaration and Initialization

• Declaring an array requires the type, the name, and the number of elements

Example: numeric count[20]• Individual array elements must be initialized• If elements will contain different values, initialize

each element separately• Some languages allow declaration and initialization

in a single statement

Example: numeric count[0] = 5


Array Declaration and Initialization Array Declaration and Initialization (continued(continued))

• If all elements in an array will have the same initial value, use a loop

• Providing values for an array is called populating the array


Initialized and Uninitialized ArraysInitialized and Uninitialized Arrays

• Uninitialized array: does not receive values for the elements until run time

• Initialized array: values for the elements are “hard-coded” by the programmer

• An array can be thought of as a table


Initialized and Uninitialized Arrays Initialized and Uninitialized Arrays (continued)(continued)


Loading an Array from a FileLoading an Array from a File

• Hard-coded values are inconvenient – only the programmer can change them

• Initializing an array by reading values from a file makes the program more flexible


Loading an Array from a File Loading an Array from a File (continued)(continued)


Searching an Array for an Exact MatchSearching an Array for an Exact Match

• Use a loop to search through an array, element by element

• The loop control variable can be used as the array subscript variable

• Flag: a variable used to indicate if an event has occurred

• Start with flag = “No”; set it to “Yes” if you find the desired value in an array element


Searching an Array for an Exact Match Searching an Array for an Exact Match (continued)(continued)


Using Parallel ArraysUsing Parallel Arrays

• Parallel arrays: two arrays in which each element in one array is associated with the element in the same relative position in the other array

Example: one array holds product numbers, the other holds the prices for each product


Using Parallel Arrays (continued)Using Parallel Arrays (continued)


Improving Search Efficiency Improving Search Efficiency Using an Early ExitUsing an Early Exit

• When using a loop to search an array, exit the loop if the item is found in an array element

• Early Exit: leaving a loop when a match is found


Improving Search Efficiency Improving Search Efficiency Using an Early Exit (continued)Using an Early Exit (continued)


Using a Constant Using a Constant to Store an Array Sizeto Store an Array Size

• Instead of hard-coding the array size, use a named constant or variable

• Advantage: only the variable or constant needs to be changed to change the array size

• Named constant identifiers should be written in all caps

Example: NUM_PRODUCTS


Using a Constant Using a Constant to Store an Array Size (continued)to Store an Array Size (continued)


Searching an Array for a Range MatchSearching an Array for a Range Match

• Range match: finding a value within a contiguous range of values

Example: range is 0 through 8


Searching an Array Searching an Array for a Range Match (continued)for a Range Match (continued)


SummarySummary

• Array: a series of variables in memory which all have the same name but different subscripts

• Each array element has a unique subscript to identify it from other array elements

• Subscript (or index): a number indicating the position of the element within the array

• Use a variable for the subscript to allow more programmatic control of the array


Summary (continued)Summary (continued)

• Array element values can be hard-coded, or assigned at run time

• Array element values can be loaded from a file• Searching an array involves examining each

element– Loop through all elements– Use a flag to indicate when the matching value

is found• Flag: a variable that indicates if an event has

occurred


Summary (continued)Summary (continued)

• Parallel arrays are two arrays in which each element of one array is related to the element in the same subscript position in the other array

• When comparing a range of values, use either the low-end or high-end values of each range

an object-oriented approach to programming logic and design chapter 7 arrays

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