Chapter 9 OneDimensional Numeric Arrays

1
Chapter 9 One-Dimensional Numeric Arrays
2
Array

• Data structure
• Grouping of like-type data
• Indicated with brackets containing positive
  integer constant or expression following
  identifier
• Subscript or index
• Loops commonly used for manipulation

Lesson 9.1
3
One-Dimensional Arrays

• Declaration indicates name and reserves space for
  all elements
• Values assigned to array elements using
  assignment statements
• Array names classified as identifiers
• Programmer sets size of array explicitly

Lesson 9.1
4
Array Length

• Determined by expression or value enclosed in
  brackets in declaration
• General form for declaration type
  namevalue
• Value in brackets can be constant variable,
  expression, or literal

const int N 26 double bN
int a25 int b52
Lesson 9.1
5
Array Length

• Must be integer constant greater than 0
• Only integer type variables (with modifiers)
• int, char
• signed, unsigned, short, long
• Always within brackets following identifier
• Examples int c32
  int c-25, b43.5

Valid
Lesson 9.1
6
Array Subscripts

• First index or subscript is 0
• int a2
• Data type of elements is int
• Name of array is a
• Number of elements is 2
• Valid subscripts are 0 and 1
• Address as a0 and a1

Lesson 9.1
7
Printing Array Elements

• Use cout
• Treat like single variable
• Print one element at a time
• Example cout ltlt "a0 " ltlt a0 ltlt endl

Lesson 9.1
8
Initialization

• In declarations enclosed in curly braces

int a5 11,22
Declares array a and initializes first two
elements and all remaining set to zero
int b 1,2,8,9,5
Declares array b and initializes all elementsand
sets the length of the array to 5
Lesson 9.2
9
Working With Arrays

• Remember subscripts must calculate to an integral
  value
• Normally use loop to control array processing
• Common loop is for loop
• Start at zero
• Continue while loop control variable lt N
• N is the size of the array

Lesson 9.2
10
Using An Array

• Declare int test3
• sets aside 3 storage locations
• use index to reference the variables
• test0 86
• test1 92
• test2 90

86
92
90
Lesson 9.2
11
Example

• Declare and fill an array which will hold 5
  double numbers double
  num5 for (int a 0 a lt 5 a) cin
  gtgt numa

Initialize by readingfrom the keyboard
Lesson 9.2
12
Input/Output

• Typically use files
• Reading from file, number of elements ?
• Guard against reading past end of file
• Use function eof( ) which returns 1 when end
• Reading from file, number of elements known

Lesson 9.3
13
Loop to Read Data Into an Array
Number of elements unknown!
for (j 0 !infile1.eof ( ) j)
infile1 gtgt aj
Example of for loop
Lesson 9.3
14
Loop to Read Data Into an Array
Number of elements unknown!
length 0 infile gtgt data while ((length lt
max_array_size) ! infile.eof ( ))
alength data length infile gtgt
data
Example of while loop
Lesson 9.3
15
File Input with Known Number of Elements
infile1 gtgt num_elem for (j 0 j lt num_elem
j) infile1 gtgt aj
First line of file contains number of array
elements.
16
File Input Sentinel Value

• Particular predefined value contained in file
  that indicates end of data group
• Loop and read data value by value until sentinel
  is read

for (j 0 aj ! -1 j)
infile1 gtgt aj
17
Loop to Print Data From Array(scores is array of
20 test scores)
for (int j 0 j lt 20 j)
cout ltlt scores j ltlt endl
Lesson 9.3
18
Arrays and Functions

• Pass address of array to function instead of
  element values
• Function declaration
• Data type and empty brackets int
• Function call
• Array name with no brackets x
• Function header
• Data type, name, and empty brackets int x

Lesson 9.4
19
Passing Array Information

• Three pieces of information
• Size of single array element
• Indicated by data type
• Address of array
• Indicated by array name in function call
• Location to store array address
• Indicated by identifier followed by brackets in
  function header

Lesson 9.4
20
General Form
rtype function (type , int) function (array,
num) rtype function (type b , int num_elem)
Declaration
Call
Header
Lesson 9.4
21
Classes with Array Data Members

• Automatically made accessible to public class
  member functions
• Use enumeration to size data member arrays
• Comma-separated list of identifiers
• Identifier automatically assigned constant
  integer value
• Value assigned depends on order in enumeration
  list

Lesson 9.5
22
Enumeration

• Keyword enum
• Makes code more readable
• Example enum sun 1, mon, tues, wed, thur,
  fri, sat
• Assigns integer constant 1 to sun, 2 to mon, etc.
• Example of usage int day
  day wed

Same as day 4
Lesson 9.5
23
Find Smallest Value in Array
small scores 0 for (int j 1 j lt 20 j)
if (scores j lt small)
small scores j
Lesson 9.5
24
Arrays of Objects

• Declared using class name, object name, and
  brackets enclosing integer constant
  Vehicle truck3
• Three objects (truck0, truck1, truck2 of
  class Vehicle
• Call member function
• object, dot operator, and function name
• truck0.set_data (50, 2, 3)

Lesson 9.6
25
Arrays of Objects

• Good when multiple pieces of information are
  linked
• Use assignment statement to copy one object array
  element to another
• truck1 truck0

Lesson 9.6
26
Summary
Learned how to

• Create and manipulate arrays
• Trace and debug loops that manipulate arrays
• Reserve memory during program execution
• Use arrays to solve problems