1
Arrays
2
Chapter 12 Topics
One-Dimensional Arrays
Using const in Function Prototypes
Using an Array of struct or class Objects
Using an enum Index Type for an Array
Special Kinds of Array Processing
Two-Dimensional Arrays
Passing Two-Dimensional Arrays as Arguments
Another Way of Defining Two-Dimensional
Arrays
Multidimensional Arrays
3
C++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
4
Structured Data Type
A structured data type is a type that
stores a collection of individual
components with one variable name
and allows individual components to
be stored and retrieved
5
Declare variables to
store and total 3 blood pressures
int bp1,bp2,bp3;
int total;
40024000 4004
bp2bp1 bp3
cin >> bp1 >> bp2 >> bp3;
total = bp1 + bp2 + bp3;
6
What if you wanted to store and total
1000 blood pressures?
int bp[ 1000 ] ;
// declares an array of 1000 int values
bp[0] bp[1] bp[2],,,,bp[999]
5000 5002 5004 5006
.,,,
7
One-Dimensional Array
Definition
An array is a structured collection of components
(called array elements),all of the same data type,
given a single name,and stored in adjacent
memory locations.
The individual components are accessed by using
the array name together with an integral valued
index in square brackets.
The index indicates the position of the component
within the collection.
8
Difference Between Array and
Struct or class
As array is a structure,an array differs from
struct or class in two fundamental was:
1,An array is a homogeneous data
structure,whereas structs and classes are
heterogeneous types.
2,A component of an array is accessed by its
position in the structure,whereas a
component of a struct or class is accessed by
an identifier.
9
Another Example
Declare an array called temps which will hold
up to 5 individual float values.
float temps[5]; // declaration allocates memory
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
number of elements in the array
indexes or subscripts
Base Address
10
Declaration of an Array
the index is also called the subscript
in C++,the first array element always has
subscript 0,The second array element has
subscript 1,etc.
the base address of an array is its beginning
address in memory
SYNTAX
DataType ArrayName [ConstIntExpression];
11
Yet Another Example
Declare an array called name which will hold up
to 10 individual char values.
char name[10]; // declaration allocates memory
number of elements in the array
name[0] name[1] name[2] name[3] name[4],,,,,name[9]
6000 6001 6002 6003 6004 6005 6006 6007 6008 6009
Base Address
12
Assigning Values to
Individual Array Elements
float temps[ 5 ] ; // allocates memory for array
int m = 4 ;
temps[ 2 ] = 98.6 ;
temps[ 3 ] = 101.2 ;
temps[ 0 ] = 99.4 ;
temps[ m ] = temps[ 3 ] / 2.0 ;
temps[ 1 ] = temps[ 3 ] - 1.2 ; // what value is assigned?
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
99.4? 98.6 101.2 50.6
13
What values are assigned?
float temps[ 5 ] ; // allocates memory for array
int m ;
for (m = 0; m < 5; m++)
{
temps[ m ] = 100.0 + m * 0.2 ;
}
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
14
Now what values are printed?
float temps[ 5 ] ; // allocates memory for array
int m ;
.,,,,
for (m = 4; m >= 0; m-- )
{
cout << temps[ m ] << endl ;
}
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
100.0 100.2 100.4 100.6 100.8
15
Variable Subscripts
float temps[ 5 ] ; // allocates memory for array
int m = 3 ;
.,,,,,
What is temps[ m + 1]?
What is temps[ m ] + 1?
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
100.0 100.2 100.4 100.6 100.8
16
A Closer Look at the Compiler
float temps[5]; // this declaration allocates memory
To the compiler,the value of the identifier temps
alone is the base address of the array,We say
temps is a pointer (because its value is an
address),It,points” to a memory location.
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
100.0 100.2 100.4 100.6 100.8
17
Out-of-Bounds Array Indexes
Out-of-Bounds array indexes,an
index value that,in C++,is either less
than 0 or greater than the array size
minus 1.
18
Initializing Array in a
Declaration
int ages[ 5 ] = { 40,13,20,19,36 } ;
for ( int m = 0; m < 5; m++ )
{
cout << ages[ m ] ;
}
ages[0] ages[1] ages[2] ages[3] ages[4]
6000 6002 6004 6006 6008
40 13 20 19 36
19
In C++,
No Aggregate Array Operations
the only thing you can do with an entire
array as a whole (aggregate) with any
type of component elements is to pass
it as an argument to a function
EXCEPTION,aggregate I/O is permitted
for C strings (special kinds of char
arrays)
20
Passing Arrays as Arguments
in C++,arrays are always passed by
reference
whenever an array is passed as an
argument,its base address- the memory
address of the first element of an array -
is sent to the called function
21
Using Arrays as
Arguments to Functions
Generally,functions that work with arrays
require 2 items of information as arguments:
the beginning memory address of the array
(base address)
the number of elements to process in the
array
22
Assertions About Arrays
In assertions written as comments,we often
need to refer to a range of array elements:
// Assert,alpha [i] through alpha [j] have been
printed
or,
// Assert,alpha [i]..alpha [j] have been printed
or,
// Assert,alpha [i..j] have been printed
23
Using Typedef with Arrays
We can use Typedef to give a name to
an array type.
Example,
typedef float FloatArr [100] ;
24
#include <iomanip>
#include <iostream>
void Obtain ( int [ ],int ) ; // prototypes here
void FindWarmest ( const int[ ],int,int & ) ;
void FindAverage ( const int[ ],int,int & ) ;
void Print ( const int [ ],int ) ;
using namespace std ;
int main ( )
{
int temp[31] ; // array to hold up to 31 temperatures
int numDays ;
int average ;
int hottest ;
int m ;
Example with Array Parameters
25
cout <<,How many daily temperatures?,;
cin >> numDays ;
Obtain( temp,numDays ) ; // call passes value of numDays and
// address of array temp to function
cout << numDays <<,temperatures,<< endl ;
Print ( temp,numDays ) ;
FindAverage ( temp,numDays,average ) ;
FindWarmest ( temp,numDays,hottest ) ;
cout << endl <<,Average was:,<< average << endl ;
cout <<,Highest was:,<< hottest << endl ;
return 0 ;
}
Example continued
26
Memory Allocated for Array
temp[0] temp[1] temp[2] temp[3] temp[4],,,,,temp[30]
6000
Base Address
50 65 70 62 68,,,,,,
int temp[31] ; // array to hold up to 31 temperatures
27
void Obtain ( /* out */ int temp [ ],
/* in */ int number )
// Has user enter number temperature values at keyboard
// Precondition:
// number is assigned && number > 0
// Postcondition:
// temp [ 0,,number -1 ] are assigned
{
int m;
for ( m = 0 ; m < number; m++ )
{
cout <<,Enter a temperature,,;
cin >> temp [m] ;
}
}
28
void Print ( /* in */ const int temp [ ],
/* in */ int number )
// Prints number temperature values to screen
// Precondition:
// number is assigned && number > 0
// temp [0,,number -1 ] are assigned
// Postcondition:
// temp [ 0,,number -1 ] have been printed 5 to a line
{
int m;
cout <<,You entered:,;
for ( m = 0 ; m < number; m++ )
{
if ( m % 5 == 0 )
cout << endl ;
cout << setw(7) << temp [m] ;
}
}
29
Use of const
because the identifier of an array holds the
base address of the array,an & is never
needed for an array in the parameter list
arrays are always passed by reference
to prevent elements of an array used as an
argument from being unintentionally
changed by the function,you place const
in the function heading and prototype
30
Use of const in prototypes
void Obtain ( int [ ],int ) ;
void FindWarmest ( const int [ ],int,int & ) ;
void FindAverage ( const int [ ],int,int & ) ;
void Print ( const int [ ],int ) ;
do not use const with outgoing array because
function is supposed to change array values
use const with incoming array values to
prevent unintentional changes by function
31
void FindAverage ( /* in */ const int temp [ ],
/* in */ int number,
/* out */ int & avg )
// Determines average of temp[0,,number-1]
// Precondition:
// number is assigned && number > 0
// temp [0,,number -1 ] are assigned
// Postcondition:
// avg == arithmetic average of temp[0,,number-1]
{
int m;
int total = 0;
for ( m = 0 ; m < number; m++ )
{
total = total + temp [m] ;
}
avg = int (float (total) / float (number) +,5) ;
}
32
void FindWarmest ( /* in */ const int temp [ ],
/* in */ int number,
/* out */ int & largest )
// Determines largest of temp[0,,number-1]
// Precondition:
// number is assigned && number > 0
// temp [0,,number -1 ] are assigned
// Postcondition:
// largest== largest value in temp[0,,number-1]
{
int m;
largest = temp[0] ; // initialize largest to first element
// then compare with other elements
for ( m = 0 ; m < number; m++ )
{
if ( temp [m] > largest )
largest = temp[m] ;
}
}
33
Using arrays for Counters
Write a program to count the number of
each alphabet letter in a text file.
letter ASCII
A? 65
B? 66
C? 67
D? 68
.,
.,
.,
Z? 90
This is my text file.
It contains many
things!
5 + 8 is not 14.
Is it?
A:\my.dat
34
const int SIZE 91;
int freqCount[SIZE];
freqCount [ 0 ] 0
freqCount [ 1] 0
.,
.,
.,
freqCount [ 65 ] 2
freqCount [ 66 ] 0
.,
.,
.,
freqCount [ 89] 1
freqCount [ 90 ] 0
unused
counts?A? and?a?
counts?B? and?b?
,
,
,
counts? Y? and?y?
counts?Z? and?z?
35
Main Module Pseudocode
Level 0
Open dataFile (and verify success)
Zero out freqCount
Read ch from dataFile
WHILE NOT EOF on dataFile
If ch is alphabetic character
If ch is lowercase alphabetic
Change ch to uppercase
Increment freqCount[ch] by 1
Read ch from dataFile
Print characters and frequencies
36
// Program counts frequency of each alphabetic character in text file.
#include < fstream >
#include < iostream >
#include < cctype >
const int SIZE 91;
void PrintOccurrences ( const int [ ] ) ; // prototype
using namespace std ;
Counting Frequency of
Alphabetic Characters
37
int main ( )
{
ifstream dataFile ;
int freqCount [SIZE ] ;
char ch ;
char index;
dataFile.open (,A:\\my.dat” ) ; // open and verify success
if ( ! dataFile )
{
cout <<,CAN?T OPEN INPUT FILE !,<< endl;
return 1;
}
for ( int m = 0; m < SIZE; m++ ) // zero out the array
freqCount [ m ] = 0 ;
38
// read file one character at a time
dataFile.get ( ch ) ; // priming read
while ( dataFile ) // while last read was successful
{
if (isalpha ( ch ) )
{
if ( islower ( ch ) )
ch = toupper ( ch ) ;
freqCount [ ch ] = freqCount [ ch ] + 1 ;
}
dataFile,get ( ch ) ; // get next character
}
PrintOccurrences ( freqCount ) ;
return 0;
}
39
void PrintOccurrences ( /* in */ const int freqCount [ ] )
// Prints each alphabet character and its frequency
// Precondition:
// freqCount [ ‘A’,,‘Z’ ] are assigned
// Postcondition:
// freqCount [ ‘A’,,‘Z’ ] have been printed
{ char index ;
cout <<,File contained,<< endl ;
cout <<,LETTER OCCURRENCES” << endl ;
for ( index =?A? ; index < =?Z? ; index ++ )
{
cout << setw ( 4 ) << index << setw ( 10 )
<< freqCount [ index ] << endl ;
}
}
40
More about Array Index
array index can be any integral type,This includes
char and enum types
it is programmer?s responsibility to make sure that
an array index does not go out of bounds,The index
must be within the range 0 through the declared
array size minus one
using an index value outside this range causes the
program to access memory locations outside the
array,The index value determines which memory
location is used
41
Array with enum Index Type
DECLARATION
enum Department { WOMENS,MENS,CHILDRENS,
LINENS,HOUSEWARES,ELECTRONICS };
float salesAmt [ 6 ] ;
Department which;
USE
for ( which = WOMENS ; which <= ELECTRONICS ;
which = Department ( which + 1 ) )
cout << salesAmt [ which ] << endl;
42
float salesAmt[6];
salesAmt [ WOMENS ] ( i,e,salesAmt [ 0 ] )
salesAmt [ MENS] ( i,e,salesAmt [ 1 ] )
salesAmt [ CHILDRENS ] ( i,e,salesAmt [ 2 ] )
salesAmt [ LINENS ] ( i,e,salesAmt [ 3 ] )
salesAmt [ HOUSEWARES ] ( i,e,salesAmt [ 4 ] )
salesAmt [ ELECTRONICS ] ( i,e,salesAmt [ 5 ] )
43
Parallel Arrays
DEFINITION
Parallel arrays are 2 or more arrays that have the same
index range,and whose elements contain related
information,possibly of different data types.
EXAMPLE
const int SIZE 50 ;
int idNumber [ SIZE ] ;
float hourlyWage [ SIZE ] ; parallel arrays
44
const int SIZE 50 ;
int idNumber [ SIZE ] ; // parallel arrays hold
float hourlyWage [ SIZE ] ; // related information
idNumber [ 0 ] 4562 hourlyWage [ 0 ] 9.68
idNumber [ 1 ] 1235 hourlyWage [ 1 ] 45.75
idNumber [ 2 ] 6278 hourlyWage [ 2 ] 12.71
.,,,
.,,,
.,,,
idNumber [ 48 ] 8754 hourlyWage [ 48 ] 67.96
idNumber [ 49 ] 2460 hourlyWage [ 49 ] 8.97
45
Array of Structures
const int MAX_SIZE = 500 ;
enum HealthType { Poor,Fair,Good,Excellent } ;
struct AnimalType // declares struct data type
{
long id ;
string name ;
string genus ;
string species ;
string country ; // 8 struct members
int age ;
float weight ;
HealthType health ;
} ;
AnimalType bronxZoo [ MAX_SIZE ] ; // declares array
46
AnimalType bronxZoo[MAX_SIZE];
bronxZoo
[ 0 ]
[ 1 ]
.,
.,
.,
[ 498 ]
[ 499 ]
bronxZoo [ 0 ].id 3456219
bronxZoo [ 0 ].name,camel”
bronxZoo [ 0 ].genus,Camelus”
bronxZoo [ 0 ].species,dromedarius”
bronxZoo [ 0 ].country,India”
bronxZoo [ 0 ].age 10
bronxZoo [ 0 ].weight 992.8
bronxZoo [ 0 ].health Fair
47
AnimalType bronxZoo[MAX_SIZE];
.id,name,genus,species,country,age,weight,health
bronxZoo [ 0 ] 3456219,camel”,Camelus”“dromedarius”,India” 10 992.8 Fair
bronxZoo [ 1 ]
bronxZoo [ 2 ]
bronxZoo [ 3 ]
.,
.,
.,
bronxZoo[498]
bronxZoo[499]
48
Add 1 to the age member of each
element of the bronxZoo array
for ( j = 0 ; j < MAX_SIZE ; j++ )
bronxZoo[ j ].age = bronxZoo[ j ].age + 1 ;
OR,
for ( j = 0 ; j < MAX_SIZE ; j++ )
bronxZoo[ j ].age++ ;
49
Find total weight of all elements of
the bronxZoo array
float total = 0.0 ;
for ( j = 0 ; j < MAX_SIZE ; j++ )
total += bronxZoo[ j ].weight ;
50
Specification of TimeType
class TimeType // timetype.h
{
public,// 7 function members
void Set ( int hours,int minutes,int seconds ) ;
void Increment ( ) ;
void Write ( ) const ;
Boolean Equal ( TimeType otherTime ) const ;
Boolean LessThan ( TimeType otherTime ) const ;
TimeType ( int initHrs,int initMins,int initSecs ) ; // constructor
TimeType ( ) ; // default constructor
private,// 3 data members
int hrs ;
int mins ;
int secs ;
} ;
51
TimeType Class Instance Diagram
Private data:
hrs
mins
secs
Set
Increment
Write
Equal
LessThan
18
30
0
class TimeType
TimeType
TimeType
52
Arrays of Records
const int MAX_STUDENTS = 150 ;
enum Gradetype {A,B,C,D,F} ;
struct StudentRec
{
string stuName ;
float gpa;
int examScore [4] ;
GradeType courseGrade ;
}
StudentRec gradeBook [MAX_STUDENTS] ;
int count ;
Each component of gradeBook is a record of type
StudentRec.
53
Array of Class Objects
const int MAX_SIZE = 50 ;
// declare array of class objects
TimeType trainSchedule[ MAX_SIZE ] ;
The default constructor,if there is any constructor,
is invoked for each element of the array.
54
Special Kinds of Array
Processing
Subarray Processing,using only part of
the declared array.
Indexes with Semantic Content,using
index values that have specific meaning
within the problem.
55
Two-Dimensional Array
is a collection of components,all of the same type,
structured in two dimensions,(referred to as
rows and columns),Individual components are
accessed by a pair of indexes representing the
component?s position in each dimension.
DataType ArrayName [ConstIntExpr] [ConstIntExpr],,,;
SYNTAX FOR ARRAY DECLARATION
56
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
66 64 72 78 85 90 99 105 98 90 88 80row 2,
col 7
might be
Arizona?s
high for
August
EXAMPLE -- To keep monthly high temperatures for
all 50 states in one array,
const int NUM_STATES = 50 ;
const int NUM_MONTHS = 12 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
[ 0 ]
[ 1 ]
[ 2 ]
.
,stateHighs [2] [7]
.
[ 48 ]
[ 49 ]
57
[JAN],,,[AUG],,[DEC]
66 64 72 78 85 90 99 105 98 90 88 80row 2,
col AUG
could be
Arizona?s
high for
August
enum MonthType { JAN,FEB,MAR,APR,MAY,JUN,
JUL,AUG,SEP,OCT,NOV,DEC } ;
const int NUM_MONTHS = 12 ;
const int NUM_STATES = 50 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
[ 0 ]
[ 1 ]
[ 2 ]
.
,stateHighs [2] [AUG]
.
[ 48 ]
[ 49 ]
58
enum StateType { AL,AK,AZ,AR,CA,CO,CT,DE,FL,GA,HI,ID,IL,IN,
IA,KS,KY,LA,ME,MD,MA,MI,MN,MS,MO,MT,NE,NV,NH,NJ,NM,
NY,NC,ND,OH,OK,OR,PA,RI,SC,SD,TN,TX,UT,VT,VA,WA,WV,
WI,WY };
enum MonthType { JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,
SEP,OCT,NOV,DEC } ;
const int NUM_MONTHS = 12 ;
const int NUM_STATES = 50 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
[ AL]
[ AK]
[ AZ]
.
,stateHighs [AZ] [AUG]
.
[ WI ]
[ WY]
[JAN],,,[AUG],,[DEC]
66 64 72 78 85 90 99 105 98 90 88 80row AZ,
col AUG
holds
Arizona?s
high for
August
59
Finding the average high
temperature for Arizona
int total = 0 ;
int month ; // WITHOUT ENUM TYPES
int average ;
for ( month = 0 ; month < NUM_MONTHS ; month ++ )
total = total + stateHighs [ 2 ] [ month ] ;
average = int ( total / 12.0 + 0.5 ) ;
average
85
60
Finding the Average High
Temperature for Arizona
int total = 0 ;
MonthType month ; // WITH ENUM TYPES DEFINED
int average ;
for ( month = JAN ; month <= DEC ; month = MonthType( month + 1) )
total = total + stateHighs [ AZ] [ month ] ;
average = int ( total / 12.0 + 0.5 ) ;
average
85
61
const int NUM_STATES = 50 ;
const int NUM_MONTHS = 12 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
In memory,C++ stores arrays in row order,The
first row is followed by the second row,etc.
Base Address
.,,
12 highs for state 0 12 highs for state 1 etc.
Alabama Alaska
first row second row
8000 8024 8048
STORAGE rows columns
62
Processing Two-Dimensional
Arrays
Processing data in a two-dimensional array
generally means accessing the array in one of four
patterns:randomly,along rows,along columns,or
throughout the entire array.Each of these may also
involve subarray processing,
Look at these patterns of access by considering
four common examples of array processing.
1.Sum the rows.
2.Sum the columns.
3.Initialize the array to all zeros (or some special
value),
4.Print the array.
63
Passing Two-Dimensional
Arrays as Arguments
just as with a one-dimensional array,when a
two- (or higher) dimensional array is passed as
an argument,the base address of the caller?s
array is sent to the function
the size of all dimensions except the first must
be included in the function heading and
prototype
the sizes of those dimensions in the function?s
parameter list must be exactly the same as
declared for the caller?s array
64
const int NUM_STATES = 50 ;
const int NUM_MONTHS = 12 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
int stateAverages [ NUM_STATES ] ;
[ 0 ]
62 [ 1 ]
85 [ 2 ]
.
.
.
[ 48 ]
[ 49 ]
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
43 42 50 55 60 78 80 85 81 72 63 40
66 64 72 78 85 90 99 105 98 90 88 80
Write a function using the two-dimensional stateHighs array to fill
a one-dimensional stateAverages array
Alaska
Arizona
65
void FindAverages( /* in */ const int stateHighs [ ] [ NUM_MONTHS],
/* out */ int stateAverages [ ] )
// PRE,stateHighs[ 0..NUM_STATES] [ 0..NUM_MONTHS] assigned
// POST,stateAverages[ 0..NUM_STATES] contains rounded average
// high temperature for each state
{
int state;
int month;
int total;
for ( state = 0 ; state < NUM_STATES; state++ )
{
total = 0 ;
for ( month = 0 ; month < NUM_MONTHS ; month++ )
total += stateHighs [ state ] [ month ] ;
stateAverages [ state ] = int ( total / 12.0 + 0.5 ) ;
}
}
66
Using typedef with Arrays
helps eliminate the chances of size mismatches between
function arguments and parameters,FOR EXAMPLE,
typedef int StateHighsType [ NUM_STATES ] [ NUM_MONTHS ] ;
typedef int StateAveragesType [ NUM_STATES ] ;
void FindAverages( /* in */ const StateHighsType stateHighs,
/* out */ StateAveragesType stateAverages )
{
.
.
.
}
67
Viewed another way,,,
stateHighs[ 0 ] [ 0 ]
stateHighs[ 0 ] [ 1 ]
stateHighs[ 0 ] [ 2 ]
stateHighs[ 0 ] [ 3 ]
stateHighs[ 0 ] [ 4 ]
stateHighs[ 0 ] [ 5 ]
stateHighs[ 0 ] [ 6 ]
stateHighs[ 0 ] [ 7 ]
stateHighs[ 0 ] [ 8 ]
stateHighs[ 0 ] [ 9 ]
stateHighs[ 0 ] [10 ]
stateHighs[ 0 ] [11 ]
stateHighs[ 1 ] [ 0 ]
stateHighs[ 1 ] [ 1 ]
stateHighs[ 1 ] [ 2 ]
stateHighs[ 1 ] [ 3 ]
.
.
.
To locate an element such as
stateHighs [ 2 ] [ 7]
the compiler needs to know
that there are 12 columns
in this two-dimensional array.
At what address will
stateHighs [ 2 ] [ 7 ] be found?
Assume 2 bytes for type int.
Base Address 8000
68
Declaring Multidimensional Arrays
EXAMPLE OF THREE-DIMENSIONAL ARRAY
const NUM_DEPTS = 5 ; // mens,womens,childrens,electronics,furniture
const NUM_MONTHS = 12 ;
const NUM_STORES = 3 ; // White Marsh,Owings Mills,Towson
int monthlySales [ NUM_DEPTS ] [ NUM_MONTHS ] [ NUM_STORES ] ;
rows columns sheets
OR USING TYPEDEF
typedef int MonthlySalesType [NUM_DEPTS] [NUM_MONTHS] [NUM_STORES] ;
MonthlySalesType monthlySales;
69
const NUM_DEPTS = 5 ; // mens,womens,childrens,electronics,furniture
const NUM_MONTHS = 12 ;
const NUM_STORES = 3 ; // White Marsh,Owings Mills,Towson
int monthlySales [ NUM_DEPTS ] [ NUM_MONTHS ] [ NUM_STORES ] ;
monthlySales[3][7][0]
sales for electronics in August at White Marsh
12 MONTHS columns
5 D
EPT
S
ro
ws
70
COMBINED SALES FOR January
DEPT # DEPT NAME SALES $
0 Mens 8345
1 Womens 9298
2 Childrens 7645
3 Electronics 14567
4 Furniture 21016
.,
.,
.,
COMBINED SALES FOR December
DEPT # DEPT NAME SALES $
0 Mens 12345
1 Womens 13200
2 Childrens 11176
3 Electronics 22567
4 Furniture 11230
Print sales for each month by department
71
const NUM_DEPTS = 5 ; // mens,womens,childrens,electronics,furniture
const NUM_MONTHS = 12 ;
const NUM_STORES = 3 ; // White Marsh,Owings Mills,Towson
int monthlySales [NUM_DEPTS] [NUM_MONTHS] [ NUM_STORES] ;
.,,,
for ( month = 0 ; month < NUM_MONTHS ; month++ )
{
cout <<,COMBINED SALES FOR,;
WriteOut(month) ; // function call to write the name of month
cout <<,DEPT # DEPT NAME SALES $” << endl;
for (dept = 0 ; dept < NUM_DEPTS ; dept++ )
{ totalSales = 0; // sum over all stores
for (store = 0 ; store < NUM_STORES ; store++ )
totalSales = totalSales + monthlySales [dept] [month] [store] ;
WriteDeptNameAndSales(dept,totalSales ) ; // function call
}
}
72
Adding a Fourth Dimension,,,
const NUM_DEPTS = 5 ; // mens,womens,childrens,electronics,furniture
const NUM_MONTHS = 12 ;
const NUM_STORES = 3 ; // White Marsh,Owings Mills,Towson
const NUM_YEARS = 2 ;
int moreSales [NUM_DEPTS] [NUM_MONTHS] [ NUM_STORES] [NUM_YEARS] ;
moreSales[3] [7] [0] [1]year 0 year 1
for electronics,August,White Marsh,one year after starting year
Arrays
2
Chapter 12 Topics
One-Dimensional Arrays
Using const in Function Prototypes
Using an Array of struct or class Objects
Using an enum Index Type for an Array
Special Kinds of Array Processing
Two-Dimensional Arrays
Passing Two-Dimensional Arrays as Arguments
Another Way of Defining Two-Dimensional
Arrays
Multidimensional Arrays
3
C++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
4
Structured Data Type
A structured data type is a type that
stores a collection of individual
components with one variable name
and allows individual components to
be stored and retrieved
5
Declare variables to
store and total 3 blood pressures
int bp1,bp2,bp3;
int total;
40024000 4004
bp2bp1 bp3
cin >> bp1 >> bp2 >> bp3;
total = bp1 + bp2 + bp3;
6
What if you wanted to store and total
1000 blood pressures?
int bp[ 1000 ] ;
// declares an array of 1000 int values
bp[0] bp[1] bp[2],,,,bp[999]
5000 5002 5004 5006
.,,,
7
One-Dimensional Array
Definition
An array is a structured collection of components
(called array elements),all of the same data type,
given a single name,and stored in adjacent
memory locations.
The individual components are accessed by using
the array name together with an integral valued
index in square brackets.
The index indicates the position of the component
within the collection.
8
Difference Between Array and
Struct or class
As array is a structure,an array differs from
struct or class in two fundamental was:
1,An array is a homogeneous data
structure,whereas structs and classes are
heterogeneous types.
2,A component of an array is accessed by its
position in the structure,whereas a
component of a struct or class is accessed by
an identifier.
9
Another Example
Declare an array called temps which will hold
up to 5 individual float values.
float temps[5]; // declaration allocates memory
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
number of elements in the array
indexes or subscripts
Base Address
10
Declaration of an Array
the index is also called the subscript
in C++,the first array element always has
subscript 0,The second array element has
subscript 1,etc.
the base address of an array is its beginning
address in memory
SYNTAX
DataType ArrayName [ConstIntExpression];
11
Yet Another Example
Declare an array called name which will hold up
to 10 individual char values.
char name[10]; // declaration allocates memory
number of elements in the array
name[0] name[1] name[2] name[3] name[4],,,,,name[9]
6000 6001 6002 6003 6004 6005 6006 6007 6008 6009
Base Address
12
Assigning Values to
Individual Array Elements
float temps[ 5 ] ; // allocates memory for array
int m = 4 ;
temps[ 2 ] = 98.6 ;
temps[ 3 ] = 101.2 ;
temps[ 0 ] = 99.4 ;
temps[ m ] = temps[ 3 ] / 2.0 ;
temps[ 1 ] = temps[ 3 ] - 1.2 ; // what value is assigned?
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
99.4? 98.6 101.2 50.6
13
What values are assigned?
float temps[ 5 ] ; // allocates memory for array
int m ;
for (m = 0; m < 5; m++)
{
temps[ m ] = 100.0 + m * 0.2 ;
}
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
14
Now what values are printed?
float temps[ 5 ] ; // allocates memory for array
int m ;
.,,,,
for (m = 4; m >= 0; m-- )
{
cout << temps[ m ] << endl ;
}
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
100.0 100.2 100.4 100.6 100.8
15
Variable Subscripts
float temps[ 5 ] ; // allocates memory for array
int m = 3 ;
.,,,,,
What is temps[ m + 1]?
What is temps[ m ] + 1?
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
100.0 100.2 100.4 100.6 100.8
16
A Closer Look at the Compiler
float temps[5]; // this declaration allocates memory
To the compiler,the value of the identifier temps
alone is the base address of the array,We say
temps is a pointer (because its value is an
address),It,points” to a memory location.
temps[0] temps[1] temps[2] temps[3] temps[4]
7000 7004 7008 7012 7016
100.0 100.2 100.4 100.6 100.8
17
Out-of-Bounds Array Indexes
Out-of-Bounds array indexes,an
index value that,in C++,is either less
than 0 or greater than the array size
minus 1.
18
Initializing Array in a
Declaration
int ages[ 5 ] = { 40,13,20,19,36 } ;
for ( int m = 0; m < 5; m++ )
{
cout << ages[ m ] ;
}
ages[0] ages[1] ages[2] ages[3] ages[4]
6000 6002 6004 6006 6008
40 13 20 19 36
19
In C++,
No Aggregate Array Operations
the only thing you can do with an entire
array as a whole (aggregate) with any
type of component elements is to pass
it as an argument to a function
EXCEPTION,aggregate I/O is permitted
for C strings (special kinds of char
arrays)
20
Passing Arrays as Arguments
in C++,arrays are always passed by
reference
whenever an array is passed as an
argument,its base address- the memory
address of the first element of an array -
is sent to the called function
21
Using Arrays as
Arguments to Functions
Generally,functions that work with arrays
require 2 items of information as arguments:
the beginning memory address of the array
(base address)
the number of elements to process in the
array
22
Assertions About Arrays
In assertions written as comments,we often
need to refer to a range of array elements:
// Assert,alpha [i] through alpha [j] have been
printed
or,
// Assert,alpha [i]..alpha [j] have been printed
or,
// Assert,alpha [i..j] have been printed
23
Using Typedef with Arrays
We can use Typedef to give a name to
an array type.
Example,
typedef float FloatArr [100] ;
24
#include <iomanip>
#include <iostream>
void Obtain ( int [ ],int ) ; // prototypes here
void FindWarmest ( const int[ ],int,int & ) ;
void FindAverage ( const int[ ],int,int & ) ;
void Print ( const int [ ],int ) ;
using namespace std ;
int main ( )
{
int temp[31] ; // array to hold up to 31 temperatures
int numDays ;
int average ;
int hottest ;
int m ;
Example with Array Parameters
25
cout <<,How many daily temperatures?,;
cin >> numDays ;
Obtain( temp,numDays ) ; // call passes value of numDays and
// address of array temp to function
cout << numDays <<,temperatures,<< endl ;
Print ( temp,numDays ) ;
FindAverage ( temp,numDays,average ) ;
FindWarmest ( temp,numDays,hottest ) ;
cout << endl <<,Average was:,<< average << endl ;
cout <<,Highest was:,<< hottest << endl ;
return 0 ;
}
Example continued
26
Memory Allocated for Array
temp[0] temp[1] temp[2] temp[3] temp[4],,,,,temp[30]
6000
Base Address
50 65 70 62 68,,,,,,
int temp[31] ; // array to hold up to 31 temperatures
27
void Obtain ( /* out */ int temp [ ],
/* in */ int number )
// Has user enter number temperature values at keyboard
// Precondition:
// number is assigned && number > 0
// Postcondition:
// temp [ 0,,number -1 ] are assigned
{
int m;
for ( m = 0 ; m < number; m++ )
{
cout <<,Enter a temperature,,;
cin >> temp [m] ;
}
}
28
void Print ( /* in */ const int temp [ ],
/* in */ int number )
// Prints number temperature values to screen
// Precondition:
// number is assigned && number > 0
// temp [0,,number -1 ] are assigned
// Postcondition:
// temp [ 0,,number -1 ] have been printed 5 to a line
{
int m;
cout <<,You entered:,;
for ( m = 0 ; m < number; m++ )
{
if ( m % 5 == 0 )
cout << endl ;
cout << setw(7) << temp [m] ;
}
}
29
Use of const
because the identifier of an array holds the
base address of the array,an & is never
needed for an array in the parameter list
arrays are always passed by reference
to prevent elements of an array used as an
argument from being unintentionally
changed by the function,you place const
in the function heading and prototype
30
Use of const in prototypes
void Obtain ( int [ ],int ) ;
void FindWarmest ( const int [ ],int,int & ) ;
void FindAverage ( const int [ ],int,int & ) ;
void Print ( const int [ ],int ) ;
do not use const with outgoing array because
function is supposed to change array values
use const with incoming array values to
prevent unintentional changes by function
31
void FindAverage ( /* in */ const int temp [ ],
/* in */ int number,
/* out */ int & avg )
// Determines average of temp[0,,number-1]
// Precondition:
// number is assigned && number > 0
// temp [0,,number -1 ] are assigned
// Postcondition:
// avg == arithmetic average of temp[0,,number-1]
{
int m;
int total = 0;
for ( m = 0 ; m < number; m++ )
{
total = total + temp [m] ;
}
avg = int (float (total) / float (number) +,5) ;
}
32
void FindWarmest ( /* in */ const int temp [ ],
/* in */ int number,
/* out */ int & largest )
// Determines largest of temp[0,,number-1]
// Precondition:
// number is assigned && number > 0
// temp [0,,number -1 ] are assigned
// Postcondition:
// largest== largest value in temp[0,,number-1]
{
int m;
largest = temp[0] ; // initialize largest to first element
// then compare with other elements
for ( m = 0 ; m < number; m++ )
{
if ( temp [m] > largest )
largest = temp[m] ;
}
}
33
Using arrays for Counters
Write a program to count the number of
each alphabet letter in a text file.
letter ASCII
A? 65
B? 66
C? 67
D? 68
.,
.,
.,
Z? 90
This is my text file.
It contains many
things!
5 + 8 is not 14.
Is it?
A:\my.dat
34
const int SIZE 91;
int freqCount[SIZE];
freqCount [ 0 ] 0
freqCount [ 1] 0
.,
.,
.,
freqCount [ 65 ] 2
freqCount [ 66 ] 0
.,
.,
.,
freqCount [ 89] 1
freqCount [ 90 ] 0
unused
counts?A? and?a?
counts?B? and?b?
,
,
,
counts? Y? and?y?
counts?Z? and?z?
35
Main Module Pseudocode
Level 0
Open dataFile (and verify success)
Zero out freqCount
Read ch from dataFile
WHILE NOT EOF on dataFile
If ch is alphabetic character
If ch is lowercase alphabetic
Change ch to uppercase
Increment freqCount[ch] by 1
Read ch from dataFile
Print characters and frequencies
36
// Program counts frequency of each alphabetic character in text file.
#include < fstream >
#include < iostream >
#include < cctype >
const int SIZE 91;
void PrintOccurrences ( const int [ ] ) ; // prototype
using namespace std ;
Counting Frequency of
Alphabetic Characters
37
int main ( )
{
ifstream dataFile ;
int freqCount [SIZE ] ;
char ch ;
char index;
dataFile.open (,A:\\my.dat” ) ; // open and verify success
if ( ! dataFile )
{
cout <<,CAN?T OPEN INPUT FILE !,<< endl;
return 1;
}
for ( int m = 0; m < SIZE; m++ ) // zero out the array
freqCount [ m ] = 0 ;
38
// read file one character at a time
dataFile.get ( ch ) ; // priming read
while ( dataFile ) // while last read was successful
{
if (isalpha ( ch ) )
{
if ( islower ( ch ) )
ch = toupper ( ch ) ;
freqCount [ ch ] = freqCount [ ch ] + 1 ;
}
dataFile,get ( ch ) ; // get next character
}
PrintOccurrences ( freqCount ) ;
return 0;
}
39
void PrintOccurrences ( /* in */ const int freqCount [ ] )
// Prints each alphabet character and its frequency
// Precondition:
// freqCount [ ‘A’,,‘Z’ ] are assigned
// Postcondition:
// freqCount [ ‘A’,,‘Z’ ] have been printed
{ char index ;
cout <<,File contained,<< endl ;
cout <<,LETTER OCCURRENCES” << endl ;
for ( index =?A? ; index < =?Z? ; index ++ )
{
cout << setw ( 4 ) << index << setw ( 10 )
<< freqCount [ index ] << endl ;
}
}
40
More about Array Index
array index can be any integral type,This includes
char and enum types
it is programmer?s responsibility to make sure that
an array index does not go out of bounds,The index
must be within the range 0 through the declared
array size minus one
using an index value outside this range causes the
program to access memory locations outside the
array,The index value determines which memory
location is used
41
Array with enum Index Type
DECLARATION
enum Department { WOMENS,MENS,CHILDRENS,
LINENS,HOUSEWARES,ELECTRONICS };
float salesAmt [ 6 ] ;
Department which;
USE
for ( which = WOMENS ; which <= ELECTRONICS ;
which = Department ( which + 1 ) )
cout << salesAmt [ which ] << endl;
42
float salesAmt[6];
salesAmt [ WOMENS ] ( i,e,salesAmt [ 0 ] )
salesAmt [ MENS] ( i,e,salesAmt [ 1 ] )
salesAmt [ CHILDRENS ] ( i,e,salesAmt [ 2 ] )
salesAmt [ LINENS ] ( i,e,salesAmt [ 3 ] )
salesAmt [ HOUSEWARES ] ( i,e,salesAmt [ 4 ] )
salesAmt [ ELECTRONICS ] ( i,e,salesAmt [ 5 ] )
43
Parallel Arrays
DEFINITION
Parallel arrays are 2 or more arrays that have the same
index range,and whose elements contain related
information,possibly of different data types.
EXAMPLE
const int SIZE 50 ;
int idNumber [ SIZE ] ;
float hourlyWage [ SIZE ] ; parallel arrays
44
const int SIZE 50 ;
int idNumber [ SIZE ] ; // parallel arrays hold
float hourlyWage [ SIZE ] ; // related information
idNumber [ 0 ] 4562 hourlyWage [ 0 ] 9.68
idNumber [ 1 ] 1235 hourlyWage [ 1 ] 45.75
idNumber [ 2 ] 6278 hourlyWage [ 2 ] 12.71
.,,,
.,,,
.,,,
idNumber [ 48 ] 8754 hourlyWage [ 48 ] 67.96
idNumber [ 49 ] 2460 hourlyWage [ 49 ] 8.97
45
Array of Structures
const int MAX_SIZE = 500 ;
enum HealthType { Poor,Fair,Good,Excellent } ;
struct AnimalType // declares struct data type
{
long id ;
string name ;
string genus ;
string species ;
string country ; // 8 struct members
int age ;
float weight ;
HealthType health ;
} ;
AnimalType bronxZoo [ MAX_SIZE ] ; // declares array
46
AnimalType bronxZoo[MAX_SIZE];
bronxZoo
[ 0 ]
[ 1 ]
.,
.,
.,
[ 498 ]
[ 499 ]
bronxZoo [ 0 ].id 3456219
bronxZoo [ 0 ].name,camel”
bronxZoo [ 0 ].genus,Camelus”
bronxZoo [ 0 ].species,dromedarius”
bronxZoo [ 0 ].country,India”
bronxZoo [ 0 ].age 10
bronxZoo [ 0 ].weight 992.8
bronxZoo [ 0 ].health Fair
47
AnimalType bronxZoo[MAX_SIZE];
.id,name,genus,species,country,age,weight,health
bronxZoo [ 0 ] 3456219,camel”,Camelus”“dromedarius”,India” 10 992.8 Fair
bronxZoo [ 1 ]
bronxZoo [ 2 ]
bronxZoo [ 3 ]
.,
.,
.,
bronxZoo[498]
bronxZoo[499]
48
Add 1 to the age member of each
element of the bronxZoo array
for ( j = 0 ; j < MAX_SIZE ; j++ )
bronxZoo[ j ].age = bronxZoo[ j ].age + 1 ;
OR,
for ( j = 0 ; j < MAX_SIZE ; j++ )
bronxZoo[ j ].age++ ;
49
Find total weight of all elements of
the bronxZoo array
float total = 0.0 ;
for ( j = 0 ; j < MAX_SIZE ; j++ )
total += bronxZoo[ j ].weight ;
50
Specification of TimeType
class TimeType // timetype.h
{
public,// 7 function members
void Set ( int hours,int minutes,int seconds ) ;
void Increment ( ) ;
void Write ( ) const ;
Boolean Equal ( TimeType otherTime ) const ;
Boolean LessThan ( TimeType otherTime ) const ;
TimeType ( int initHrs,int initMins,int initSecs ) ; // constructor
TimeType ( ) ; // default constructor
private,// 3 data members
int hrs ;
int mins ;
int secs ;
} ;
51
TimeType Class Instance Diagram
Private data:
hrs
mins
secs
Set
Increment
Write
Equal
LessThan
18
30
0
class TimeType
TimeType
TimeType
52
Arrays of Records
const int MAX_STUDENTS = 150 ;
enum Gradetype {A,B,C,D,F} ;
struct StudentRec
{
string stuName ;
float gpa;
int examScore [4] ;
GradeType courseGrade ;
}
StudentRec gradeBook [MAX_STUDENTS] ;
int count ;
Each component of gradeBook is a record of type
StudentRec.
53
Array of Class Objects
const int MAX_SIZE = 50 ;
// declare array of class objects
TimeType trainSchedule[ MAX_SIZE ] ;
The default constructor,if there is any constructor,
is invoked for each element of the array.
54
Special Kinds of Array
Processing
Subarray Processing,using only part of
the declared array.
Indexes with Semantic Content,using
index values that have specific meaning
within the problem.
55
Two-Dimensional Array
is a collection of components,all of the same type,
structured in two dimensions,(referred to as
rows and columns),Individual components are
accessed by a pair of indexes representing the
component?s position in each dimension.
DataType ArrayName [ConstIntExpr] [ConstIntExpr],,,;
SYNTAX FOR ARRAY DECLARATION
56
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
66 64 72 78 85 90 99 105 98 90 88 80row 2,
col 7
might be
Arizona?s
high for
August
EXAMPLE -- To keep monthly high temperatures for
all 50 states in one array,
const int NUM_STATES = 50 ;
const int NUM_MONTHS = 12 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
[ 0 ]
[ 1 ]
[ 2 ]
.
,stateHighs [2] [7]
.
[ 48 ]
[ 49 ]
57
[JAN],,,[AUG],,[DEC]
66 64 72 78 85 90 99 105 98 90 88 80row 2,
col AUG
could be
Arizona?s
high for
August
enum MonthType { JAN,FEB,MAR,APR,MAY,JUN,
JUL,AUG,SEP,OCT,NOV,DEC } ;
const int NUM_MONTHS = 12 ;
const int NUM_STATES = 50 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
[ 0 ]
[ 1 ]
[ 2 ]
.
,stateHighs [2] [AUG]
.
[ 48 ]
[ 49 ]
58
enum StateType { AL,AK,AZ,AR,CA,CO,CT,DE,FL,GA,HI,ID,IL,IN,
IA,KS,KY,LA,ME,MD,MA,MI,MN,MS,MO,MT,NE,NV,NH,NJ,NM,
NY,NC,ND,OH,OK,OR,PA,RI,SC,SD,TN,TX,UT,VT,VA,WA,WV,
WI,WY };
enum MonthType { JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,
SEP,OCT,NOV,DEC } ;
const int NUM_MONTHS = 12 ;
const int NUM_STATES = 50 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
[ AL]
[ AK]
[ AZ]
.
,stateHighs [AZ] [AUG]
.
[ WI ]
[ WY]
[JAN],,,[AUG],,[DEC]
66 64 72 78 85 90 99 105 98 90 88 80row AZ,
col AUG
holds
Arizona?s
high for
August
59
Finding the average high
temperature for Arizona
int total = 0 ;
int month ; // WITHOUT ENUM TYPES
int average ;
for ( month = 0 ; month < NUM_MONTHS ; month ++ )
total = total + stateHighs [ 2 ] [ month ] ;
average = int ( total / 12.0 + 0.5 ) ;
average
85
60
Finding the Average High
Temperature for Arizona
int total = 0 ;
MonthType month ; // WITH ENUM TYPES DEFINED
int average ;
for ( month = JAN ; month <= DEC ; month = MonthType( month + 1) )
total = total + stateHighs [ AZ] [ month ] ;
average = int ( total / 12.0 + 0.5 ) ;
average
85
61
const int NUM_STATES = 50 ;
const int NUM_MONTHS = 12 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
In memory,C++ stores arrays in row order,The
first row is followed by the second row,etc.
Base Address
.,,
12 highs for state 0 12 highs for state 1 etc.
Alabama Alaska
first row second row
8000 8024 8048
STORAGE rows columns
62
Processing Two-Dimensional
Arrays
Processing data in a two-dimensional array
generally means accessing the array in one of four
patterns:randomly,along rows,along columns,or
throughout the entire array.Each of these may also
involve subarray processing,
Look at these patterns of access by considering
four common examples of array processing.
1.Sum the rows.
2.Sum the columns.
3.Initialize the array to all zeros (or some special
value),
4.Print the array.
63
Passing Two-Dimensional
Arrays as Arguments
just as with a one-dimensional array,when a
two- (or higher) dimensional array is passed as
an argument,the base address of the caller?s
array is sent to the function
the size of all dimensions except the first must
be included in the function heading and
prototype
the sizes of those dimensions in the function?s
parameter list must be exactly the same as
declared for the caller?s array
64
const int NUM_STATES = 50 ;
const int NUM_MONTHS = 12 ;
int stateHighs [ NUM_STATES ] [ NUM_MONTHS ] ;
int stateAverages [ NUM_STATES ] ;
[ 0 ]
62 [ 1 ]
85 [ 2 ]
.
.
.
[ 48 ]
[ 49 ]
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
43 42 50 55 60 78 80 85 81 72 63 40
66 64 72 78 85 90 99 105 98 90 88 80
Write a function using the two-dimensional stateHighs array to fill
a one-dimensional stateAverages array
Alaska
Arizona
65
void FindAverages( /* in */ const int stateHighs [ ] [ NUM_MONTHS],
/* out */ int stateAverages [ ] )
// PRE,stateHighs[ 0..NUM_STATES] [ 0..NUM_MONTHS] assigned
// POST,stateAverages[ 0..NUM_STATES] contains rounded average
// high temperature for each state
{
int state;
int month;
int total;
for ( state = 0 ; state < NUM_STATES; state++ )
{
total = 0 ;
for ( month = 0 ; month < NUM_MONTHS ; month++ )
total += stateHighs [ state ] [ month ] ;
stateAverages [ state ] = int ( total / 12.0 + 0.5 ) ;
}
}
66
Using typedef with Arrays
helps eliminate the chances of size mismatches between
function arguments and parameters,FOR EXAMPLE,
typedef int StateHighsType [ NUM_STATES ] [ NUM_MONTHS ] ;
typedef int StateAveragesType [ NUM_STATES ] ;
void FindAverages( /* in */ const StateHighsType stateHighs,
/* out */ StateAveragesType stateAverages )
{
.
.
.
}
67
Viewed another way,,,
stateHighs[ 0 ] [ 0 ]
stateHighs[ 0 ] [ 1 ]
stateHighs[ 0 ] [ 2 ]
stateHighs[ 0 ] [ 3 ]
stateHighs[ 0 ] [ 4 ]
stateHighs[ 0 ] [ 5 ]
stateHighs[ 0 ] [ 6 ]
stateHighs[ 0 ] [ 7 ]
stateHighs[ 0 ] [ 8 ]
stateHighs[ 0 ] [ 9 ]
stateHighs[ 0 ] [10 ]
stateHighs[ 0 ] [11 ]
stateHighs[ 1 ] [ 0 ]
stateHighs[ 1 ] [ 1 ]
stateHighs[ 1 ] [ 2 ]
stateHighs[ 1 ] [ 3 ]
.
.
.
To locate an element such as
stateHighs [ 2 ] [ 7]
the compiler needs to know
that there are 12 columns
in this two-dimensional array.
At what address will
stateHighs [ 2 ] [ 7 ] be found?
Assume 2 bytes for type int.
Base Address 8000
68
Declaring Multidimensional Arrays
EXAMPLE OF THREE-DIMENSIONAL ARRAY
const NUM_DEPTS = 5 ; // mens,womens,childrens,electronics,furniture
const NUM_MONTHS = 12 ;
const NUM_STORES = 3 ; // White Marsh,Owings Mills,Towson
int monthlySales [ NUM_DEPTS ] [ NUM_MONTHS ] [ NUM_STORES ] ;
rows columns sheets
OR USING TYPEDEF
typedef int MonthlySalesType [NUM_DEPTS] [NUM_MONTHS] [NUM_STORES] ;
MonthlySalesType monthlySales;
69
const NUM_DEPTS = 5 ; // mens,womens,childrens,electronics,furniture
const NUM_MONTHS = 12 ;
const NUM_STORES = 3 ; // White Marsh,Owings Mills,Towson
int monthlySales [ NUM_DEPTS ] [ NUM_MONTHS ] [ NUM_STORES ] ;
monthlySales[3][7][0]
sales for electronics in August at White Marsh
12 MONTHS columns
5 D
EPT
S
ro
ws
70
COMBINED SALES FOR January
DEPT # DEPT NAME SALES $
0 Mens 8345
1 Womens 9298
2 Childrens 7645
3 Electronics 14567
4 Furniture 21016
.,
.,
.,
COMBINED SALES FOR December
DEPT # DEPT NAME SALES $
0 Mens 12345
1 Womens 13200
2 Childrens 11176
3 Electronics 22567
4 Furniture 11230
Print sales for each month by department
71
const NUM_DEPTS = 5 ; // mens,womens,childrens,electronics,furniture
const NUM_MONTHS = 12 ;
const NUM_STORES = 3 ; // White Marsh,Owings Mills,Towson
int monthlySales [NUM_DEPTS] [NUM_MONTHS] [ NUM_STORES] ;
.,,,
for ( month = 0 ; month < NUM_MONTHS ; month++ )
{
cout <<,COMBINED SALES FOR,;
WriteOut(month) ; // function call to write the name of month
cout <<,DEPT # DEPT NAME SALES $” << endl;
for (dept = 0 ; dept < NUM_DEPTS ; dept++ )
{ totalSales = 0; // sum over all stores
for (store = 0 ; store < NUM_STORES ; store++ )
totalSales = totalSales + monthlySales [dept] [month] [store] ;
WriteDeptNameAndSales(dept,totalSales ) ; // function call
}
}
72
Adding a Fourth Dimension,,,
const NUM_DEPTS = 5 ; // mens,womens,childrens,electronics,furniture
const NUM_MONTHS = 12 ;
const NUM_STORES = 3 ; // White Marsh,Owings Mills,Towson
const NUM_YEARS = 2 ;
int moreSales [NUM_DEPTS] [NUM_MONTHS] [ NUM_STORES] [NUM_YEARS] ;
moreSales[3] [7] [0] [1]year 0 year 1
for electronics,August,White Marsh,one year after starting year
