Transcript PowerPoint Slides for Starting Out with C++ Early Objects

Chapter 8: Arrays
Starting Out with C++
Early Objects
Seventh Edition
by Tony Gaddis, Judy Walters,
and Godfrey Muganda
Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Topics
8.1
8.2
8.3
8.4
8.5
8.6
Arrays Hold Multiple Values
Accessing Array Elements
Inputting and Displaying Array Contents
Array Initialization
Processing Array Contents
Using Parallel Arrays
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Topics (continued)
8.7 The typedef Statement
8.8 Arrays as Function Arguments
8.9 Two-Dimensional Arrays
8.10 Arrays with Three or More Dimensions
8.12 Arrays of Class Objects
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8.1 Arrays Hold Multiple Values
• Array: variable that can store multiple
values of the same type
• Values are stored in adjacent memory
locations
• Declared using [] operator
const int CAP = 5;
int test[CAP]; … or int test[5];
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Array Storage in Memory
The definition
int test[5];
allocates the following memory cells:
Element 0
Element 1
Element 2
Element 3
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Element 4
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Array Terminology
In the definition int test[5];
– int is the data type of each array element
– test is the name of the array
– 5, in [5], is the capacity declarator, the
maximum number of elements the array can hold.
– The size of an array is the number of bytes
allocated for it
(number of elements) * (bytes needed for each element)
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Array Terminology Examples
Examples:
Assumes int uses 4 bytes and double uses 8 bytes
const int CAP = 5, DSIZE = 10;
int test[CAP];
// holds 5 ints, array
// occupies 20 bytes
double vol[DSIZE];// holds 10 doubles
// array is 80 bytes
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8.2 Accessing Array Elements
• Each array element is a variable whose
“name” contains a subscript that uniquely
identifies the element.
• Name of 3rd element array test is test[2],
”test-sub-two”
• Subscripts start at 0
subscripts
0
1
2
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3
4
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Accessing Array Elements
Array elements are regular variables of the
base data type.
test
0
test[0]
cout <<
cin >>
test[4]
cout <<
1
2
3
4
= 79;
test[0];
test[1];
= test[0] + test[1];
test; // illegal due to ??
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8.3 Inputting and Displaying
Array Contents
Arrays can be loaded and displayed – one
element at a time.
int test[5]; // 5-element array
cout << "Enter first test score ";
cin >> test[0];
for (k=0; k<5; k++) cout << test[k];
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Array Subscripts
• Array subscript can be an integer constant,
variable, or expression
• Examples:
Subscript is
cin >> test[3];
int constant
cout << test[i];
int variable
cout << test[i+j];
int expression
cin >> test[test[0]];
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int expression
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Inputting and Displaying
All Array Elements
To access each element of an array
– Use a (for) loop
– The loop control variable sequence must be
the array valid subscripts, e.g., 0,1,2,…
– A different array element will be referenced
each time through the loop
for (i = 0; i < 5; i++)
sum = sum + test[i];
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WARNING!! No Bounds Checking
• C++ does not check that an array subscript is
in range
• An invalid array subscript can cause program
to overwrite other memory
• Example:
int i = 4;
int num[3];
num[i] = 25;
num
25
[0] [1] [2]
• C++ Segmentation error!!
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Off-By-One Errors
• Most often occur when a program accesses
data one position beyond the start/end of
an array, or misses the first/element of an
array.
• Don’t confuse the ordinal number of an
array element (first, second, third) with its
subscript (0, 1, 2)
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8.4 Array Initialization
• Can be initialized during program execution
with assignment statements
test[0] = 79;
test[1] = 82; // etc.
• Can be initialized at array definition with an
initialization list
int test[5] = {79,82,91,77,84};
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Partial Array Initialization
• If array is initialized at definition with fewer
values than the size declarator of the array,
remaining elements will be set to 0 or NULL
int test[5] = {79, 82};
79
82
0
0
0
• Initial values used in order; cannot skip over
elements to initialize noncontiguous range
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Implicit Array Sizing
• Can determine array size by the size of the
initialization list
short quizzes[]={12,17,15,11};
12
17
15
11
• Must use either array size declarator or
initialization list when array is defined
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8.5 Processing Array Contents
• Array elements can be
– treated as ordinary variables of the same type
as the array
– used in arithmetic operations, in relational
expressions, etc.
• Example:
if (principalAmt[3] >= 10000)
interest = principalAmt[3] * intRate1;
else
interest = principalAmt[3] * intRate2;
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Using Increment and Decrement
Operators with Array Elements
int test[15];
When using ++ and -- operators, don’t
confuse the element with the subscript
test[i]++; // increments test[i], but has
// no effect on i.
test[i++]; // increments i, but has
// no effect on test array.
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Copying One Array to Another
• Can not copy with an assignment
statement:
test2 = test;
//won’t work
• Instead, must use a loop to copy element
by element:
for (int k=0; k < CAP; k++)
test2[k] = test[k];
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Are Two Arrays Equal?
• Also, cannot compare in a single expression:
if (test2 == test)
• Use a while loop with a boolean flag:
bool Equal = true;
int k = 0;
while (k< CAP && Equal)
{
if(test[k] != test2[k])Equal = false;
k++;
}
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Are Two Arrays Equal? Another Way?
• Use a while loop with a boolean flag:
bool Equal = true;
int k = 0;
while (k < CAP)
{
Equal = ( test[k] == test2[k]);
k++;
}
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Are Two Arrays Equal? And This?
• Use a while loop with a boolean flag:
bool Equal = true;
int k = 0;
while (k < CAP)
{
Equal = Equal && (test[k]==test2[k]);
k++;
}
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Are Two Arrays Equal? - Again
• Use a for loop with a boolean flag:
bool Equal = true;
int k = 0;
for (k=0; Equal && k<CAP; k++)
{
if(test[k] != test2[k])
Equal = false;
}
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Sum, Average of Array Elements
• Use a simple loop to add together array
elements
float average, sum = 0;
for(int t=0; t<CAP; t++)
sum += test[t];
• Once summed, average can be computed
average = sum/CAP;
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Largest Array Element
• Use a loop to examine each element and find
the largest element (i.e., one with the largest value)
int largest = test[0];
for (int t = 1; t < CAP; t++)
{ if (test[t] > largest)
largest = test[t];
}
cout << "Highest score is " << largest;
• A similar algorithm exists to find smallest.
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Partially-Filled Arrays
• The exact amount of data may not be known
when a program is written.
• Programmer estimates maximum amount of
data (capacity), and sizes array accordingly.
• Programmer must track the number of array
elements actually being used – to avoid
exceeding array capacity (segmentation error)
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C-Strings and string Objects
Can be processed using array name
– Entire string at once, or
– One element at a time by using a subscript
string city;
cout << "Enter city name: ";
cin >> city;
'S'
city[0]
'a'
'l'
'e'
'm'
city[1] city[2] city[3] city[4]
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8.6 Using Parallel Arrays
• Parallel arrays: two or more arrays that
contain related data
• Subscript is used to relate corresponding
data
– elements at same subscript are related
• The arrays may hold different data types
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Parallel Array Example
const int CAP = 5;
string name[CAP];
// student name
float average[CAP]; // course average
char grade[CAP];
// course grade
name
0
1
2
3
4
average
0
1
2
3
4
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grade
0
1
2
3
4
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Parallel Array Processing
const int CAP = 5;
string name[CAP];
// student name
float average[CAP]; // course average
char grade[CAP];
// course grade
...
for (int i = 0; i < CAP; i++)
cout << " Student: " << name[i]
<< " Average: " << average[i]
<< " Grade: "
<< grade[i]
<< endl;
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8.7 The typedef Statement
• Creates an alias for a data type.
• Format:
typedef existingType newName;
• Example:
typedef float Money;
Money Paycheck[CAP]; // array of
// floats.
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Uses of typedef
• Can make code more readable.
• Can be used to create alias for array of a
particular type
// Define yearArray as a data type
// that is an array of 12 ints
typedef int yearArray[MONTHS];
// Create two of these arrays
yearArray highTemps, lowTemps;
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8.8 Arrays as Function Arguments
• To declare a function with an array parameter,
use empty [] to indicate the argument is an array.
• To pass an array argument to a function, just
use the array name
// Function prototype
void showScores(int []);
// Function header
void showScores(int test[])
// Function call
showScores(test);
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Passing an Array Element
• Passing a single array element to a function is no
different than passing a regular variable of that
data type
• Function does not need to know that the value it
receives is coming from an array
displayValue(score[i]);
// call
void displayValue(int item) // header
{ cout << item << endl;
}
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Passing an Entire Array
• Use the array name, without any brackets,
as the argument
• Can also pass the array size so the function
knows how many elements to process
showScores(test, 5);
// call
void showScores(int[], int); // prototype
void showScores(int A[],
int size) // header
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Using typedef with a Passed Array
Can use typedef to simplify function prototype
and heading
// Make intArray an integer array
// of unspecified size
typedef int intArray[];
// Function prototype
void showScores(intArray, int);
// Function header
void showScores(intArray test, int size)
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Modifying Arrays in Functions
• Array parameters are passed by reference
• Changes made to array in a function are
made to the actual array in the calling function
• Must be careful that an array is not
inadvertently changed by a function
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8.9 Two-Dimensional Arrays
• Can define one array for multiple sets of data
• Like a table in a spreadsheet
• Use two size declarators in definition
int exam[4][3];
Number
of rows
Number
of cols
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Two-Dimensional Array Representation
int exam[4][3];
columns
exams[0][0] exams[0][1] exams[0][2]
r
o
w
s
exams[1][0] exams[1][1] exams[1][2]
exams[2][0] exams[2][1] exams[2][2]
exams[3][0] exams[3][1] exams[3][2]
Must use two subscripts to access element
exam[2][2] = 86;
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Initialization at Definition
• Two-dimensional arrays are initialized rowby-row
int exam[2][2] = { {84, 78},
{92, 97} };
84 78
92 97
• exam[0] is row 1, an int array
containing {84, 78}.
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Passing a Two-Dimensional Array to a
Function
• Use array name as argument in function call
getExams(exam, 2);
• Use empty [] for row and a size declarator for col in
the prototype and header
// Prototype, where #cols is 2
void getExams(int[][2], int);
// Header
void getExams (int Ex[][2], int rows)
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Using typedef with a
Two-Dimensional Array
Can use typedef for simpler notation
typedef int intExams[][2];
...
// Function prototype
void getExams(intExams, int);
// Function header
void getExams(intExams exam, int rows)
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2D Array Traversal
• Use nested loops, one for row and one for
column, to visit each array element.
for (int r=0; r<NROWS; r++)
for (int c=0; c<NCOLS; c++)
process exam[r][c] …
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8.10 Arrays with Three or More
Dimensions
• Can define arrays with any number of
dimensions
short rectSolid [2][3][5];
double timeGrid[3][4][3][4];
• When used as parameter, specify size of
all but 1st dimension
void getRectSolid(short [][3][5]);
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8.13 Arrays of Structures
• Structures can be used as array elements
struct Student
{
int studentID;
string name;
short year;
double gpa;
};
Student Class[30]; // Holds 30
// Student records.
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Arrays of Structures
• Use array subscript [ ] to access a specific
structure in the array
• Then use dot . operator to access members
of that structure
cin
>> Class[25].studentID;
cout << Class[i].name << " has GPA "
<< Class[i].gpa << endl;
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Chapter 8: Arrays
Starting Out with C++
Early Objects
Seventh Edition
by Tony Gaddis, Judy Walters,
and Godfrey Muganda
Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
8.14 Arrays of Class Objects
• Class objects can also be used as array elements
class Square
{ private:
int side;
public:
Square(int s = 1)
{ side = s; }
int getSide()
{ return side; }
};
Square shapes[10]; // Create array of 10
// Square objects
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Arrays of Class Objects
• First, use an array subscript [ ] to access a
specific object in the array
• Then, use dot . operator to access the
member of that object
for (i = 0; i < 10; i++)
cout << shapes[i].getSide() << endl;
object
member
function
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