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Chapter 7

Arrays

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Topics

7.1 Arrays Hold Multiple Values

7.2 Accessing Array Elements

7.3 No Bounds Checking in C++

7.4 Array Initialization

7.5 Processing Array Contents

7.6 Using Parallel Arrays

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Topics

7.7 Arrays as Function Arguments

7.8 Two-Dimensional Arrays

7.9 Arrays of Strings

7.10 Arrays with Three or More Dimensions

7.11 Introduction to the STL vector

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7.1 Arrays Hold Multiple Values

An array allows you to store and work with multiple values of the same data type

Array: variable that can store multiple values of the same type

Values are stored in adjacent memory locations

Declared using [] operator:int tests[5];

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Array - Memory Layout

The definition: int tests[5];

allocates the following memory:

first element

second element

third element

fourth element

fifth element

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Array Terminology

In the definition int tests[5]; int is the data type of the array elements tests is the name of the array 5, in [5], is the size declarator. It shows the

number of elements in the array. The size of an array is

(number of elements) * (size of each element)

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Array Terminology

The size of an array is: the total number of bytes allocated for it (number of elements) * (number of bytes for each

element) Examples:

Array Declaration Number of Elements

Size of Each Element

Size of the Array

char letters[25]; 25 1 byte 25 bytes short rings[100]; 100 2 bytes 200 bytes int miles[84]; 84 4 bytes 336 bytes float temp[12]; 12 4 bytes 48 bytes doubledDistance[1000]; 1000 8 bytes 8000 bytes

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7.2 Accessing Array Elements Each array element has a subscript, used to

access the element. Subscripts start at 0

0 1 2 3 4subscripts:

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Accessing Array Elements

Array elements can be used as regular variables: tests[0] = 79;

cout << tests[0];

cin >> tests[1];

tests[4] = tests[0] + tests[1]; Arrays must be accessed via individual elements

(except character array) :cout << tests; // not legal

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Accessing Array Contents

Can access element with constant subscript:cout << tests[3] << endl;

Can use integer expression as subscript:for (i = 0; i < 5; i++)

cout << tests[i] << endl;

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Global vs. Local Array

Global array all elements initialized to 0 Local array all elements uninitialized by

default Examples:

Program 7-1 Program 7-2

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7.3 No Bounds Checkingin C++

C++ does not check if an array subscript is in the range of values for subscripts of the array

Can access memory using subscripts that is before or after the memory for an array

Can corrupt other memory locations, crash program, or lock up computer

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7.3 No Bounds Checkingin C++ Example: Prog. 7-3

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7.4 Array Initialization

Can be initialized during program execution with assignment statements:

tests[0] = 79; tests[1] = 82; // etc.

Can be initialized at array definition with an initialization list:

int tests[5] = {79,82,91,77,84}; Initialization list cannot exceed array size Examples:

Prog. 7-4, Prog. 7-5

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Partial Array Initialization

If array is initialized at definition with fewer initial values than the size declarator of the array, the remaining elements will be set to 0:

int tests[5] = {79, 82}; Initial values used in order; cannot skip over

elements to initialize noncontiguous range

Example: Prog. 7-6

79 82 0 0 0

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Implicit Array Sizing

Can determine array size by the size of the initialization list:

short quizzes[]={12,17,15,11};

Must use either array size declarator or initialization list at array definition

12 17 15 11

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Initializing With a String

Character array can be initialized by enclosing string in " ":

char fName[6] = "Henry"; Must leave room for \0 at end of array If initializing character-by-character, must add

in \0 explicitly:char fName[6] =

{ 'H', 'e', 'n', 'r', 'y', '\0'}; Example: Prog 7-7

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7.5 Processing Array Contents

Individual array elements are processed like any other type of variable

Array elements can be treated as ordinary variables of the same type as the array

When using ++, -- operators, don’t confuse the element with the subscript:

tests[i]++; // add 1 to tests[i]tests[i++]; // increment i, no

// effect on tests Example: Prog. 7-8

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Array Assignment

To copy one array to another, don’t try to assign one array to the other:

newTests = tests; assign element-by-element:

for (i=0; i<5; i++)

newTests[i] = tests[i];

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Display the Contents of an Array

Can display character array by using its name:cout << fName << endl;

For other types of arrays, must go element-by-element:

for (i=0; i<5; i++)

cout << tests[i] << endl;

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Sum of Array Elements

Use a simple loop to add together array elements:

int tnum;float average, sum = 0;for(tnum = 0; tnum < 5; tnum++)

sum += tests[tnum]; Once summed, can compute average:

average = sum/5; Example: Prog 7-9

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7.6 Using Parallel Arrays

Parallel Arrays: two or more arrays that contain related data

Subscript is used to relate arrays: elements at same subscript are related

Arrays may be of different types

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Parallel Array Example

string name[5]; // student name

float average[5];// course average

char grade[5]; // course grade

...

for(int i = 0; i < 5; i++)

cout << "Student: " << name[i]

<< " average: " << average[i]

<< " grade: " << grade[i]

<< endl;

Example Prog. 7-10

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7.7 Arrays as Function Arguments

Pass one element of an array to a function Example Prog. 7-11

To pass an array as an argument to a function, pass the name of the array:

showScores(tests); To define a function that takes an array parameter, use

empty [] for array argument:void showScores(int []);

// function prototypevoid showScores(int tests[])

// function header

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Arrays as Function Arguments

When passing an array to a function, it is common to pass array size so that function knows how many elements to process:

showScores(tests, 5); //function call Array size must also be reflected in prototype, header:

void showScores(int [], int);

// function prototype

void showScores(int tests[], int size)

// function header Examples Prog. 7-12 & Prog. 7-13

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Modifying Arrays in Functions

Array names in functions are similar to reference variables – changes made to array in a function are reflected in actual array in calling function

Need to exercise caution that array is not inadvertently changed by a function

Example Prog. 7-14 Useful array functions: total, average,

highest, lowest, etc. Example Prog. 7-15

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7.8 Two-Dimensional Arrays

A two-dimensional array is like several identical arrays put together. It is useful for storing multiple sets of data.

Can define one array for multiple sets of data Like a table in a spreadsheet Use two size declarators in definition:

int exams[4][3]; First declarator is number of rows; second is

number of columns

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Two-Dimensional Array Representation

int exams[4][3];

Use two subscripts to access element:exams[2][2] = 86;

exams[0][0] exams[0][1] exams[0][2]

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]

columns

rows

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Initialization at Definition

Two-dimensional arrays are initialized row-by-row:

int exams[2][2] = { {84, 78}, {92,

97} };

Can omit inner { }, some initial values in a row – array elements without initial values will be set to 0 or NULL

84 78

92 97

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Two-Dimensional Array as Parameter, Argument

Use array name as argument in function call:getExams(exams, 2);

Use empty [] for row, size declarator for column in prototype, header:

void getExams(int [][2], int);

// prototype

void getExams(int exams[][2], int rows)

// header

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Examples

Prog 7-16 Prog 7-17 Summing

All the elements of a two-dimensional array The rows of a two-dimensional array The columns of a two-dimensional array

The contents of table1 are: 1 2 3 4 5 6 7 8 9 10 11 12The contents of table2 are: 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

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7.9 Array of Strings

Use a two-dimensional array of characters as an array of strings:

char students[3][10] = { "Ann", "Bill", "Cindy" };

Each row contains one string Can use row subscript to reference the string:

cout << students[i];

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7.10 Arrays with Three or More Dimensions

Can define arrays with any number of dimensions:

float seats[3][5][8]; When used as parameter, specify all but 1st

dimension in prototype, heading:void getRectSolid(short [][3][5]);

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More About Array

Array is passed by pointer Don’t want to change the contents of array: Insert const before the data type on the parameter lists in function prototype and function head

Programmer Defined Data Type Using typedef in global section The programmer defined data type will show on the

parameter lists in function prototype and function head Example

Lab 5.1 Lab 5.3