• an array is a collection of data elements of

8/14/2019 an Array is a Collection of Data Elements Of

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ARRAYS


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Arrays

An array is a collection of data elements of same typein contiguous memory e.g. list of names, list of scores

Easier way to compare and use data than havingseparate variables for data elements

data_type identifier[size] int arr[3]

declares a one-dimensional array named arrwith spacefor 3 integer variables

Variables contiguous in memory; lowest address hasfirst value, next address has second variable value,and so on


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Arrays

An individual variable within an array is called anelementof the array

The elements of an array are not named, and are

accessed by the arrays name and their position in thearray (indexingorsubcripting)

Index of first element is zero, index of lastelementissize-1 e.g. intarr[3] has variables arr[0],

arr[1] and arr[2] size has to be a positive constant (not variable)

i.e. cant do: int x = 3; int arr[x];

butcan do: int arr[3 * 2];

Number of bytes reserved with int arr[3]; ?


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Arrays

An array is an indexed data structure

An array stores a collection of variables

All variables stored in an array are of the same

data type An individual variable within an array is called an

elementof the array

An element of an array is accessed using the arrayname and an index

The name of the array is the address of the first

element. The index is the offset


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Declaring an array

data_typearray_name[size];

allocates memory forsize variables

index of first element is 0index of last element is size-1

size must be a constant


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Declaring an Array

Example: int list[10]; allocates memory for 10 integer variables index of first element is 0 index of last element is 9

C++ does not perform any bounds checking on arrayslist[0]

list[1]

list[9]


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Arrays

Arrays offer convenient means ofgrouping

together several related variables

One- dimensional arrays

type var_name[size]

int sample[10];

double d[30];

char ch[100];


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Initializing Arrays

Arrays can be initialized at the time they are

declared.

Examples:double taxrate[3] = {0.15, 0.25, 0.3};

char word[] = hello; //word has size 6

char list[5] = {h,e,l,l,o};

//list of characters, not a string

double vector[100] = {0.0}; //assigns zero to all 100 elements


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Initializing Arrays float f[5]={0.0, 1.0, 2.0, 3.0, 4.0};

//initializes f[0] to 0.0, f[1] to 1.0f[4] to 4.0 Or

float f[5]; f[0]=0.0; f[1]=1.0;

int a[10]={2}; //rest initialized to zero

cout


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Initializing Arrays forloops used to initialize arrays

#include

int main(){int t, sample[10]; // this reserves 10 integer

elements

// load the arrayfor(t=0; t


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Initializing Arraysint a[5];

Now an indexed variable like a[1] can be used anywhere that a variable of typeint can be used

int a[5];

cin >> a[4] >> a[2];

cout a[0];int max; max = a[3] + a[0]; cout next;

a[1]= next; cout


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//Reads in 5 scores, displays max_score and shows//how much each score differs from max_score

int main()

{

const int SIZE = 5;

int i, score[SIZE], max_score;

cout score[i];

if (score[i] > max_score)

max_score=score[i];

}

cout


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Initializing Arrays

Useful to give a constantname to thesize of array

/*const type modifier*/

const int NUM_EMPLOYEES = 10;

int salaries[NUM_EMPLOYEES];

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

cin >> salaries[i];

Advantage? Why not use a variable name?

Another way:

# define NUM_EMPLOYEES 10

And yes, sizeof(salaries); gives what?


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Arrays Total size of an array in bytes?

Total bytes =

number of bytes in type * number of elements

e.g. int sample[10];

Has size in bytes = 10 * sizeof(int)


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Initializing Arrays What is wrong with the following?

int num=10;

int iarray[num];

int size;

cin >> size;

int myarray[size];

double darray[5]={3.2, 4.5, 6.7, 324.0, 45.8, 23.1, 34.9}


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Assigning One Array to Another

int a[10], b[10];

// ...

a = b; // error -- illegal

/*So how do we make the contents of one array

same as the other?*/


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Assigning One Array to Another

int a[5], b[5];// ...a = b; // error illegal

Cannot assign one array to another; each element must becopied individually

const int ARRAY_SIZE = 5;int a[] = {10, 11, 12, 13, 14};

int main(){

int b[ARRAY_SIZE];for (int i=0; i < ARRAY_SIZE; ++i)

b[i] = a[i];

return 0;}


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Assigning Values to an Array

Example

int list[10];

int count;

cin >> count;

for(int i=0; i> list[i];

What if count >9?


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Summarize Arrays In C++ all arrays are stored in contiguous memory

locations

An individual element is accessed by use of an index.

An index describes theposition of an element within

an array.

In C++ all arrays have zeroas the index of their first

element.


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Arrays: Min Max

int main()

{

const int SIZE = 10;

int i, min_value, max_value;

int list[SIZE];

for(i=0; i


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Arrays

// find minimum value

min_value = list[0];

for(i=0; ilist[i])

{

min_value = list[i];}

}

cout


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Arrays// find maximum value

max_value = list[0];

for(i=0; i


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Arrays - No Bounds Checking

// An incorrect program. Do Not Execute!

int main()

{

int crash[10], i;

for(i=0; i


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What is wrong with the following?

char name[5]=class";

int myarray[];


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Arrays

int a[10] = {1,2,3,4,0,3,4,6,7,8};

int x=3; y=1;

cout


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Sorting an Array

Lots of applications require sorting

Algorithm for sorting

S ti


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Sorting an

Array

int main(void)

{


double darray[SIZE] = {34, 5.6, 0.9, 345.7, 54.1, 23.5, 2.5, 6.78, 12.4, 13.9};

int i, j;

for (i=0; idarray[j])

{

double temp;

temp = darray[i];darray[i] = darray[j];darray[j] = temp;

}}

} //inplace sorting ?

return 0;}


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Sorting an Array

// Using the bubble sort to order an array.

int main()

{


int nums[SIZE];

int a, b, t;

// give the array some random initial values

for(t=0; t


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Sorting an Array// This is the bubble sort.

for(a=1; a=a; b--)

{

if (nums[b-1] > nums[b]){ // if out of order exchange elements

t = nums[b-1];

nums[b-1] = nums[b];

nums[b] = t;

}

}

} // This is the end of the bubble sort.

} // end of main program


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Searching

Another Example -

Sequential Search

Binary Search


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Two Dimensional Arrays

C++ supports multi-dimensional array

data_type array_name[ROW_SIZE][COLUMN_SIZE]

int matrix[3][4];

row[0]

row[1]

row[2]

row1 row2 row3

in memory


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Two-D ArraysRow Major, Col Major

Row Major Storagerow[0]

row[1]

row[2]

row3

row2

row1

in memory

Col Major Storage

c[0] c[1] c[2] c[3]

c3

c2

c1

in memory

c3


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Accessing Array Elements

int matrix[3][4];

matrix has 12 integer elements

matrix[0][0] element in first row, first columnmatrix[2][3] element in last row, last column


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int main()

{

const int ROWS = 3;

const int COLS = 4;

int i, j, num[ROWS][COLS];

for(i=0; i


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Output:

1 2 3 45 6 7 8

9 10 11 12

Two Dimensional Arrays


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int main()

{

const int ROWS = 3;

const int COLS = 4;

int i, j, num[ROWS][COLS];

for(i=0; i


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Output:

1 2 3 4 5 6

7 8 9 10 11 12


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Two dimensional arrays

int E[][2]={1,2,

3,4};

Matrix Multiplication


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type name[size1][size2] . . . [sizeN];

int multidim[4][10][3];

when multidimensional arrays are used,large amounts of memory are consumed.

Multidimentional Arrays

i i i A i i i i


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int sqrs[10][2] = {

1, 1,

2, 4,

3, 9,

4, 16,

5, 25,6, 36,

7, 49,

8, 64,

9, 81,

10, 100

};

Multidimensional Array Initialization

M l idi i l A


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int main(void)

{

const int ALPHABETS = 26;

char code[ALPHABETS][2] =

{

{'a', 'f'}, {'b', 'w'}, {'c', 'x'},

{'d', 'v'}, {'e', 's'}, {'f', 'r'},{'g', 'q'}, {'h', 'c'}, {'i', 'g'},

{'j', 'h'}, {'k', 'e'}, {'l', 'u'},

{'m', 'b'}, {'n', 'j'}, {'o', 'd'},

{'p', 'k'}, {'q', 't'}, {'r', 'l'},{'s', 'm'}, {'t', 'n'}, {'u', 'a'},

{'v', 'o'}, {'w', 'p'}, {'x', 'z'},

{'y', 'i'}, {'z', 'y'}

};

Multidimensional Arrays

M ltidi i l A


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int i;

char alpha;

cout > alpha;

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

{if(code[i][0]==alpha)

{

cout


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Reference

Dietel & Dietel


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Case Study:

Computing Mean, Median and Mode Using Arrays

MeanAverage

MedianNumber in middle of sorted list

1, 2, 3, 4, 5 (3 is median)

ModeNumber that occurs most often1, 1, 1, 2, 3, 3, 4, 5 (1 is mode)

1 // Fig. 4.17: fig04_17.cpp

2 // This program introduces the topic of survey data analysis


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2 // This program introduces the topic of survey data analysis.

3 // It computes the mean, median, and mode of the data.

4 #include

5

6 using std::cout;

7 using std::endl;

8 using std::ios;9

10 #include

11

12 using std::setw;

13 using std::setiosflags;

14 using std::setprecision;

15

16voidmean( const int [], int );17voidmedian( int [], int );

18voidmode( int [], int [], int );

19voidbubbleSort( int[], int );

20voidprintArray( const int[], int );

21

22 int main()

23 {

24 const int responseSize = 99;25 int frequency[ 10 ] = { 0 },

26 response[ responseSize ] =

27 { 6, 7, 8, 9, 8, 7, 8, 9, 8, 9,

28 7, 8, 9, 5, 9, 8, 7, 8, 7, 8,

29 6, 7, 8, 9, 3, 9, 8, 7, 8, 7,

30 7, 8, 9, 8, 9, 8, 9, 7, 8, 9,

31 6, 7, 8, 7, 8, 7, 9, 8, 9, 2,

32 7, 8, 9, 8, 9, 8, 9, 7, 5, 3,

33 5 6 7 2 5 3 9 4 6 4

34 7, 8, 9, 6, 8, 7, 8, 9, 7, 8,

35 7 4 4 2 5 3 8 7 5 6


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35 7, 4, 4, 2, 5, 3, 8, 7, 5, 6,

36 4, 5, 6, 1, 6, 5, 7, 8, 7 };

37

38 mean( response, responseSize );

39 median( response, responseSize );

40 mode( frequency, response, responseSize );

41

42 return 0;

43 }

44

45voidmean( const int answer[], int arraySize )

46 {

47 int total = 0;

48

49 cout


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69

70 printArray( answer, size );

71 bubbleSort( answer, size );

72 cout


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97 for ( rating = 1; rating


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122

123 for ( int j = 0; j < size - 1; j++ )

124

125 if ( a[ j ] > a[ j + 1 ] ) {

126 hold = a[ j ];

127 a[ j ] = a[ j + 1 ];

128 a[ j + 1 ] = hold;

129 }

130}

131

132voidprintArray( const int a[], int size )

133{

134 for ( int j = 0; j < size; j++ ) {

135

136 if ( j % 20 == 0 )

137 cout


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4. Program Output

********The mean is the average value of the dataitems. The mean is equal to the total ofall the data items divided by the numberof data items (99). The mean value forthis run is: 681 / 99 = 6.8788

********Median********The unsorted array of responses is6 7 8 9 8 7 8 9 8 9 7 8 9 5 9 8 7 8 7 86 7 8 9 3 9 8 7 8 7 7 8 9 8 9 8 9 7 8 96 7 8 7 8 7 9 8 9 2 7 8 9 8 9 8 9 7 5 3

5 6 7 2 5 3 9 4 6 4 7 8 9 6 8 7 8 9 7 87 4 4 2 5 3 8 7 5 6 4 5 6 1 6 5 7 8 7

The sorted array is1 2 2 2 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5 55 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 77 7 7 7 7 7 7 7 7 7 7 7 7 8 8 8 8 8 8 88 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 89 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9

The median is element 49 ofthe sorted 99 element array.For this run the median is 7

********Mode


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Program Output

********Response Frequency Histogram

1 1 2 25 0 5 0 5

1 1 *2 3 ***3 4 ****4 5 *****5 8 ********6 9 *********7 23 ***********************8 27 ***************************9 19 *******************

The mode is the most frequent value.For this run the mode is 8 which occurred 27 times.

• an array is a collection of data elements of

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