Ch5 array nota

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Chapter 5 : ARRAY

5.1 Introduction

5.2 One Dimensional Array 5.2.1 Declaring Array

5.2.2 Array Initialization 5.2.3 Array Referencing 5.2.4 Array to Function

5.3 Two Dimensional Array 5.3.1 Two Dimensional Array Declaration

5.3.2 Two Dimensional Array Initialization5.3.3 Two Dimensional Array Referencing

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5.1 Introduction

Array is a group of memory locations related by the fact that they all have the same name & the same type.

group together

Data items a single composite data structure called array

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5.1 Introduction(Cont..)Example 1 :

To compute the average of exam score for 5 students, we need to come up with 5 identifiers.

Declaration:

int exam_score1, exam_score2, exam_score3, exam_score4, exam_score5;

Memory allocation :

exam_score1 exam_score2

exam_score3 exam_score4

exam_score5

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5.1 Introduction(Cont..)• Better use only 1 identifier to represent all 5 exam scores

& an index to specify the student to whom the exam score belongs.

• By using an array.

Declaration :int exam_score[5];

Memory allocation :

exam_score[0]exam_score[1]exam_score[2]exam_score[3]exam_score[4]

Note : The enumeration of elements(array index/subscript) within an array always start with 0 not 1.

If the array has N elements, the last elements is in position N-1.

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5.2 One Dimensional Array

• A single dimensional array

Terms :

• Array a collection of data items of the same name & data

type.• Array name

name of array that is an identifier.• Array element

Maximum no./size of array that can be stored in array.

• Array subscript/Index a value/expression enclosed in brackets after

the array name, specifying which array element to access. Must start with 0.

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5.2.1 Declaring ArrayWhen declaring arrays, we have to specify :

• Type of array• Array Name• Number of elements

Format :

data_type array_name[ number_Of_Elements ];

Example :

int exam_score[28];

Array size

Array name

Array type

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5.2.1 Declaring Array (cont)..

Another Examples :

i) int c[10];

ii) float myArray[ 3284 ];

iii) int a[5]; /* use a[0], a[1], .., a[4] */

iv) char b[3] ; /* use b[0], b[1], b[2] */

v) float c[2] = { .1, .2}; /*initialization at declaration.c[0] = 0.1 , c[1]=0.2 */

vi) double c[3][5]; /* two dimensional array

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5.2.1 Declaring Array (cont)..

• Declaring multiple arrays of same type

– Format similar to regular variables

Example:

int b[100], x[27];char car[23], lorry[45];float duck[3], ant[9];

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5.2.2 Array Initialization• Array can be initialized at compile time and run time.

(i) : Compile-Time Initialization of Arrays (while declaring)

• An initializer must be a constant value.Example :

int exam_score[4] = { 88, 85, 76, 91 }; 4 initializers, therefore 4 element array

• We also can declare the no.of element implicitly.Example :

int exam_score[ ] = {88,85,76,91}

first element is refer as exam_score[0] third element is refer as

exam_score[2]

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5.2.2 Array Initialization (cont..)

(ii) : Run-Time Initialization of Arrays

An array can be initialize at run time explicitly.

Example :

a) for (int i = 0; i < 27; i++) exam_score[i] = 0.0;

b) for( int b = 0; b < 27; b++) scanf(“%d”, &exam_score[b]);

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5.2.2 Array Initialization (cont…)

• In addition, if we leave some values of initialization, rightmost elements will become 0.

Example :

int exam_score[4] = {88,85}; -> the 3rd & 4th element are 0

int exam_score[5] = {0}; All elements are 0

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5.2.3 Array Referencing

• Each individual element is referred by specifying array name & index.

Format:arrayname[ position number ]

Example :

(i) exam_score[0] = 89;

printf( "%d", exam_score[ 0 ] );

(ii) float x[ ] = { 4.05,3.45,3.21,6.55,10.23}

for( int a = 0; a <= 4; a++) printf( “ element for index %d = %f\n”, a, x[a]); //output for the fragment code : element for index 0 = 4.05 element for index 1 = 3.45 element for index 2 = 3.21 element for index 3 = 6.55 element for index 4 = 10.23

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5.2.3 Array Referencing(cont…)

index 0 1 2 3 4 x x[0] x[1] x[2] x[3] x[4]

4.05 3.45 3.21 6.55 10.23

Name of array ( all elements of this array, have the same name, x)

Position numberof the elementwithin array x“array subscript”

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5.2.3 Array Referencing(cont…)

• Manipulation Statement using array :• Perform operations in subscript (index).

Example :

double Mark [8];

Mark [0] Mark[1] Mark[2] Mark[3] Mark [4] Mark [5] Mark [6] Mark [7]

16.0 12.0 6.0 8.0 2.5 12.0 14.0 10.5

printf (“ %.f ”, Mark[0]);

Mark[3] =25.0;

sum= Mark[0] + Mark[1];

sum += Mark[2];

Mark[3] += 1.0;

Mark[2] = Mark [0] + Mark [1];

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5.2.4 Passing Array to Function

• 2 ways to pass array to a function:

(i) pass individual element (call by value)(ii) pass the whole elements (call by reference)

(i)pass individual element (call by value)

• Pass individual element of an array.• Pass a value parameter.• Only the n element is passed by using an indexed

expression (i.e., diod[2])

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5.2.4 Passing Array to Function (cont..)

Example Program 5.4//passing individual elements#include<stdio.h>

void print_third_diod(double d);

void main( ) {double diod[5]={3.3,3.9,4.7,5.1,6.2};print_third_diod (diod[2]);

}void print_third_diod(double d){

printf("The value of the third diod is %.1f\n",d);}//Program OutputThe value of the third diod is 4.7

Pass the value of diod[2], 4.7to function print_third_diod

Copy the value of diod[2] from the main function

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(ii) pass the whole elements (call by reference) • Passing the whole array.• Passing only the name of array.• Name of array is address of first element

– Function knows where the array is stored

• At function definition, formal parameter must be an array type. Size of array does not need to be specified. (i.e., float count_average(float r[ ]) ).

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Example Program 5.5//Passing the whole array#include<stdio.h>

float count_average(float r[]);

void main( ){

float average_relay;float relay[5]={5,6,9,12,24};average_relay=count_average(relay);printf("The average of 5 relays is %.2f\n",average_relay);

}float count_average(float r[ ]){

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

total+=r[i];return(total/(float)5);

}// Program OutputThe average of 5 relays is 11.20

Entire array passed to function count_average

relay[0]relay[1]relay[2]relay[3]relay[4]

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Another example :

#include<stdio.h>void print_mark( int [ ], int, float); //Function prototype for print_markvoid main( ) {

int mark[4]; float average; mark[0] = 25; mark[1] = 35; mark[2] = 20; Entire array passed call by reference mark[3] = 20; average = (mark[0] + mark[1] + mark[2] + mark[3])/ 4; print_mark( mark, mark[2], average); } void print_mark( int m[], int a, float b) { printf(“Mark[2] is %d\n”, a); printf(“Average for 4 marks is %f\n”, b);

}

Call Function print_mark

Send the value for mark[2] ,20 to function print_mark

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5.3 Two Dimensional Array

- Array of array.

- 2-D array have 2 subscripts showing the no. of rows & the no. of column.

5.3.1 Two Dimensional Array Declaration

• Similar with 1-D declaration except it have 2 subscripts.

• Format :

Data_type array_name [no_of_element1][no_of_element2]

– data_type : either int, float, double, char.– array_name : name of array that are an identifier. – no_of_elements1 : size of array row. – no_of_elements 2 : size of column.

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5.3.1 Two Dimensional Array Declaration(cont..)

• Example :

(i) int x[10][5]; /*allocate 50 spaces (row:0-9,column:0-4)*/

(ii) float a[3][20]; /*allocate 60 spaces (row:0-2,column:0-19)*/

(iii) int exam_score[3][4]; /*allocate 12 spaces (row:0-2,column:0-3)*/

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Example :

int exam_score[3][4];

exam_score[0][0]

exam_score[0][1]

exam_score[0][2]

exam_score[0][3]

exam_score[1][0]

exam_score[1][1]

exam_score[1][2]

exam_score[1][3]

exam_score[2][0]

exam_score[2][1]

exam_score[2][2]

exam_score[2][3]

row1

row2

row3

column1 column2 column3 column4

array name row subscript column subscript

row [0]-[2] column [0]-[3]

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• The right index of an array is increased first before the left index.

• Example :int exam_score[3]

[4]={70,80,90,72,82,92,71,81,91,67,78,98 };exam_score[0][0]exam_score[0][1]exam_score[0][2]exam_score[0][3]exam_score[1][0]exam_score[1][1]exam_score[1][2]exam_score[1][3]exam_score[2][0]exam_score[2][1]exam_score[2][2]exam_score[2][3]

70

80

90

72

82

92

71

81

91

67

78

98

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5.3.2 Two Dimensional Array Initialization• We can initialize 2-D array at compile time and run time.

(i) : Compile-Time Initialization of Arrays (while declaring)

Example :

(i) int exam_score[3][4]={70,80,90,72,82,92,71,81,91,67,78,98};

• The best way : nest the data in braces to show the exact nature of the array.

Example :

(ii) int exam_score[3][4]={{70,80,90,72},{82,92,71,81},{91,67,78,98}};

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5.3.2 Two Dimensional Array Initialization(cont…)

• also can declare the far left dimension size implicitly.

Example :

(iii) int exam_score[ ][4]={{70,80,90,72},{82,92,71,81},{91,67,78,98}};

• If we leave some values out of each row, compiler initialize them to 0.

Example :

(iv) int exam_score[3 ][4]={{70,80},{82,92,71},{91,67,78,98}};

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5.3.2 Two Dimensional Array Initialization(cont..)

(ii): Run-Time Initialization

Example :int exam_score[3][4]; //array 3x4 array

• can be initialized by nested for loops. • The 1st loop varies the row from 0 - 2. • The 2nd loop varies the column from 0 - 3.

for (row=0;row<3;row++)for(column=0; column<4; column++)

scanf(“%d”,&exam_score[row][column]);//end of for

//end of for

• run the program, enter 12 values for the elements & they are stored in the appropriate locations.

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5.3.3 Two Dimensional Array Referencing

• by specifying array name & its row&column index.

• Can access elements in array, using nested for .

• Example:exam_score[0][2] = 99;exam_score[1][4]= exam_score[0][3]+10;

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5.3.3 Two Dimensional Array Referencing (cont…)

Example Program 5.8

#include<stdio.h>void main( ) {

int exam_score[3][4]={{70,80,90,72},{82,92,71,81},{91,67,78,98}};

for(int row=0; row<3; row++){ for(int column=0; column<4; column++){

exam_score[row][column]= exam_score[row][column]+1;printf("[%d][%d] = %d\n",row,column,exam_score[row]

[column]); }}

}//Program Output[0][0] = 71[0][1] = 81[0][2] = 91[0][3] = 73[1][0] = 83[1][1] = 93[1][2] = 72[1][3] = 82[2][0] = 92[2][1] = 68[2][2] = 79[2][3] = 99

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Ch5 array nota