Lecture 15 - Array

Array
Md. Imran Hossain Showrov (showrovsworld@gmail.com)
15
1

Outline
 What is An Array?
 Why do we need Array?
 Declaring An One-Dimensional Array
 Accessing Array Elements
 One-Dimensional Array
 Two-Dimensional Array

What is An Array?
 Arrays a kind of data structure that can store a fixed-
size sequential collection of elements of the same
type.
 An array is used to store a collection of data, but it is
often more useful to think of an array as a collection
of variables of the same type.

Why do we need Array?
 We can use normal variables (v1, v2, v3, ..) when we
have small number of objects, but if we want to store
large number of instances, it becomes difficult to
manage them with normal variables.The idea of array
is to represent many instances in one variable.

Defining An One-Dimensional Array
 Arrays are defined in much the same manner as
ordinary variables, except that each array name must
be accompanied by a size specification (the number of
elements).
 For one-dimensional array, the size is specified by a
positive integer expression, enclosed in square
brackets.
 The expression is usually written as
storage-class data-type array[ expression ];

Declaring An One-Dimensional Array
 Each array element can be referred to by specifying
the array name followed by one or more subscripts,
with each subscript enclosed in square brackets.
 Each subscript must be expressed as a nonnegative
integer.
 In an n-element array, the array elements are a[0],
a[1], a[2],…, a[n-1].

(cont..)
 The number of subscripts determines the
dimensionality of the array.
 Here, 3rd element is referred by a[2], nth element is
referred by a[n-1].

(Example)
 Several typical one-dimensional array definitions are shown
below:
int x[100];
char text[80];
static char message[25];
float n[12];
Here, the first line states that x is a 100-element integer array,
second line defines text to be an 80-element character array and
so on…

Initializing An One-Dimensional Array
 Arrays can be initialized C either one by one or using
a single statement as follows −
1. double balance[5] = {1000.0, 2.0, 3.4, 7.0, 50.0};
2. double balance[] = {1000.0, 2.0, 3.4, 7.0, 50.0};
 In example 1, the number of values between braces
{ } cannot be larger than the number of elements that
we declare for the array between square brackets [ ].

Accessing Array Elements
balance[4] = 50.0;
 The above statement assigns the 5th element in the array
with a value of 50.0.All arrays have 0 as the index of their
first element which is also called the base index and the
last index of an array will be total size of the array minus
1.

One-Dimensional Array Example1
#include <stdio.h>
int main () {
int n[ 10 ]; /* n is an array of 10 integers */
int i, j;
for ( i = 0; i < 10; i++ ) {/* initialize elements of array n to 0 */
n[ i ] = i + 100; /* set element at location i to i + 100 */
}
for (j = 0; j < 10; j++ ) {/* output each array element's value */
printf("Element[%d] = %dn", j, n[j] );
}
return 0;
}

(cont..)
Output:
Element[0] = 100
Element[1] = 101
Element[2] = 102
Element[3] = 103
Element[4] = 104
Element[5] = 105
Element[6] = 106
Element[7] = 107
Element[8] = 108
Element[9] = 109

int digit[4] = {1, 2, 3, 4}
float x[6] = {0, 0.25, 0, -0.50, 0, 0}
char color[3] = { ‘R’ ,‘E’ ,‘D’}
13
digit[0] = 1
digit[1] = 2
digit[2] = 3
digit[3] = 4
x[0] = 0
x[1] = 0.25
x[2] = 0
x[3] = -0.50
x[4] = 0
x[5] = 0
color[0] = ‘R’
color[1] = ‘E’
color[2] = ‘D’

int digit[] = {1, 2, 3, 4}
float x[] = {0, 0.25, 0, -0.50, 0, 0}
char color[] = { ‘R’ ,‘E’ ,‘D’}
14
digit[0] = 1
digit[1] = 2
digit[2] = 3
digit[3] = 4
x[0] = 0
x[1] = 0.25
x[2] = 0
x[3] = -0.50
x[4] = 0
x[5] = 0
color[0] = ‘R’
color[1] = ‘E’
color[2] = ‘D’

int digit[6] = {1, 2, 3, 4}
float x[6] = {0, 0.25, 0, -0.50, 0, 0}
char color[3] = { ‘R’ ,‘E’ ,‘D’}
15
digit[0] = 1
digit[1] = 2
digit[2] = 3
digit[3] = 4
digit[4] = 0
digit[5] = 0
x[0] = 0
x[1] = 0.25
x[2] = 0
x[3] = -0.50
x[4] = 0
x[5] = 0
color[0] = ‘R’
color[1] = ‘E’
color[2] = ‘D’

1. char color[3] = { “RED” }
2. char color[] = { “RED” }
16
1.
color[0] = ‘R’
color[1] = ‘E’
color[2] = ‘D’
2.
color[0] = ‘R’
color[1] = ‘E’
color[2] = ‘D’
color[2] = ‘0’

Two-dimensional Arrays
 The simplest form of multidimensional array is the two-
dimensional array.
 A two-dimensional array is, in essence, a list of one-
dimensional arrays.
 To declare a two-dimensional integer array of size [x]
[y], you would write something as follows −
type arrayName [ x ][ y ];
 Where type can be any valid C data type and arrayName will be a
valid C identifier.

Two-dimensional Arrays (cont..)
 A two-dimensional array can be considered as a table which
will have x number of rows and y number of columns.
 A two-dimensional array a, which contains three rows and four
columns can be shown as follows −

Initializing Two-Dimensional Arrays
 Multidimensional arrays may be initialized by specifying bracketed values
for each row. Following is an array with 3 rows and each row has 4
columns.
int a[3][4] = {
{0, 1, 2, 3} , /* initializers for row indexed by 0 */
{8, 9, 10, 11} /*initializers for row indexed by 2 */
};
 The nested braces, which indicate the intended row, are optional.

Initializing Two-Dimensional Arrays
int a[3][4] = {
};
We can also initialize the previous example as below:
int a[3][4] = {0,1,2,3,4,5,6,7,8,9,10,11};

Accessing Two-Dimensional Array Elements
 An element in a two-dimensional array is accessed by using the
subscripts, i.e., row index and column index of the array. For example −
int a[3][4] = {
};
 int val = a[2][3];
 The above statement will take the 4th element from the 3rd row of the
array.

Two-Dimensional Array Example1
#include <stdio.h>
int main () {
/* an array with 5 rows and 2 columns*/
int a[5][2] = { {0,0}, {1,2}, {2,4}, {3,6},{4,8}};
int i, j;
for ( i = 0; i < 5; i++ ) {
for ( j = 0; j < 2; j++ ) {
printf("a[%d][%d] = %dn", i,j, a[i][j] );
}
}
return 0;
}

Two-Dimensional Array Example1
Output:
– a[0][0]: 0
– a[0][1]: 0
– a[1][0]: 1
– a[1][1]: 2
– a[2][0]: 2
– a[2][1]: 4
– a[3][0]: 3
– a[3][1]: 6
– a[4][0]: 4
– a[4][1]: 8

Lecture 15 - Array

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