1 one dimensional arrays chapter 11 2 "all students to receive arrays!" reports dr....
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1
One Dimensional Arrays
Chapter 11
2"All students to receive arrays!" reports Dr. Austin.
Declaring arrays
scores : 85 79 92 57 68 80 . . . scores : 85 79 92 57 68 80 . . . 0 1 2 3 4 5 98 99
Inspecting arrays
Passing arrays as parameters
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Design Problem
Consider a program to calculate class average
Why??Why??
?
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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 workDescribe why this will or will NOT work
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Enter in the scores again Use 100 separate variables
» and cout and cin commands Read (then re-read) from a file The real answer …
Possible Solutions
Use arrays!!
6Simple vs Structured Data Types
Simple data type => data element contains a single value
Structured data type => a data element contains a collection of data values
x : 15x : 15 avg : 84.35avg : 84.35 ch : ‘A’ch : ‘A’
scores : 85 79 92 57 68 80scores : 85 79 92 57 68 80
name : ‘C’ ‘L’ ‘Y’ ‘D’ ‘E’name : ‘C’ ‘L’ ‘Y’ ‘D’ ‘E’
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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 80scores : 85 79 92 57 68 800 1 2 3 4 5
cout << scores[2];scores[0] = 100;cout << scores[2];scores[0] = 100;
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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
9Use of Array for Our Problem
Store elements in array as read in Go back and access for deviations
Note declarationNote declaration
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Declaring Arrays
Syntax: Data_type Array_name [constant];
Note declaration from our example
Tells how many elements set asideTells how many elements set aside
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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 . . . scores : 85 79 92 57 68 80 . . . 0 1 2 3 4 5 98 99
12Accessing Individual Components
Use the name of the array Followed by an integer expression
inside the square brackets [ ]
scores : 85 79 92 57 68 80 . . . scores : 85 79 92 57 68 80 . . . 0 1 2 3 4 5 98 99
max = scores[0];for (x = 0; x < 100; x++) if (scores[x] > max) max = scores[x];
max = scores[0];for (x = 0; x < 100; x++) if (scores[x] > max) max = scores[x];
Index can be:- constant- variable- expressionMUST be an integer
Index can be:- constant- variable- expressionMUST be an integer
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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;
float f_list [50];
f_list [100] = 123.456;
14Initializing 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 }int results [5] = {14, 6, 23, 8, 12 }
float prices [ ] = { 2.41, 85.06, 19.95, 3.91 }float prices [ ] = { 2.41, 85.06, 19.95, 3.91 }
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Aggregate Operations
Defn => 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
16Lack 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
17How 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 don’t 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
part # descrip qty price
A100 xxx 5 1.23
B25 yyy 23 8.95
0
1
2
24Testing 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
25Testing and Debugging Hints
Omitting array size in declaration» when array declared formal parameter» when array initialized at declaration
Don’t 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