Array

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Shree Swami Atmanand Saraswati Institute of Technology,
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Arrays1

Presented by:
Patel Raj G
Arrays2

Arrays
 Suppose, you need to store years of 100 cars. Will you define
100 variables?
int y1, y2,…, y100;
 An array is an indexed data structure to represent several
variables having the same data type: int y[100];
3
y[0] y[1] y[2] … y[k-1] y[k] y[k+1] … y[98] y[99]

One-Dimensional Arrays (cont’d)
 An element of an array is accessed using the array name
and an index or subscript, for example: y[5] which can be
used like a variable
 In C, the subscripts always start with 0 and increment by 1,
so y[5] is the sixth element
 The name of the array is the address of the first element
and the subscript is the offset
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y[0] y[1] y[2] … y[k-1] y[k] y[k+1] … y[98] y[99]

Definition and Initialization
 An array is defined using a declaration statement.
data_type array_name[size];
allocates memory for size elements
subscript of first element is 0
subscript of last element is size-1
size must be a constant
5

Example
int list[5];
 allocates memory for 5 integer variables
 subscript of first element is 0
 subscript of last element is 4
 C does not check bounds on arrays
 list[6] =5; /* may give segmentation fault or overwrite
other memory locations*/
6
list[0]
list[1]
list[2]
list[3]
list[4]

Initializing Arrays
 Arrays can be initialized at the time they are declared.
 Examples:
double rate[3] ={0.15, 0.25, 0.3};
char list[5] = {‘h’, ’e’, ’l’, ’l’, ’o’};
double vector[100] = {0.0}; /* assigns
zero to all 100 elements */
int s[] = {5,0,-5}; /*the size of s is 3*/
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Assigning values to an array8
For loops are often used to assign values to an array
Example:
int list[5], i;
for(i=0; i<5; i++){
list[i] = i;
}
list[0]
list[3]
list[4]
list[1]
list[2]
0
1
2
3
4
list[0]
list[1]
list[2]
list[3]
list[4]
OR
for(i=0; i<=4; i++){
list[i] = i;
}

Matrices (2D-array)
 A matrix is a set of numbers arranged in a grid with rows and
columns.
 A matrix is defined using a type declaration statement.
datatype array_name[row_size][column_size];
int matrix[3][4];
9
in memory
Column 0 Column 1 Column 2 Column 3
Row 0
Row 1
Row 2
4
1
0
2
-1
2
4
3
0
-1
3
1
4 1 0 2
-1 2 4 3
0 -1 3 1

Accessing Array Elements
int matrix[3][4];
 matrix has 12 integer elements
 matrix[0][0] element in first row, first column
 matrix[2][3] element in last row, last column
 matrix is the address of the first element
 matrix[1] is the address of the Row 1
 matrix[1] is a one dimensional array (Row 1)
10

Initialization
int x[4][4] = { {2, 3, 7, 2},
{7, 4, 5, 9},
{5, 1, 6, -3},
{2, 5, -1, 3}};
int x[][4] = { {2, 3, 7, 2},
{7, 4, 5, 9},
{5, 1, 6, -3},
{2, 5, -1, 3}};
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Initialization
int i, j, matrix[3][4];
for (i=0; i<3; i++)
for (j=0; j<4; j++)
matrix[i][j] = i;
12
j
0 1 2 3
0
1
2
i
0 0 0 0
1 1 1 1
2 2 2 2
j
0 1 2 3
0
1
2
i
0 1 2 3
0 1 2 3
0 1 2 3
matrix[i][j] = j;

Multidimensional Arrays
 An array can have many dimensions – if it has more than
one dimension, it is called a multidimensional array
 Each dimension subdivides the previous one into the
specified number of elements
 Each dimension has its own length constant
 Because each dimension is an array of array references,
the arrays within one dimension can be of different lengths
these are sometimes called ragged arrays
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Strings
 A string is an array of characters
char data[10] = “Hello”;
char data2[] = {‘H’, ‘e’, ‘l’, ‘l’, ‘o’, ‘0’}
 Use printf to print strings
printf(“%s”,data);
 Can be accessed char by char
data[0] is first character
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H e l l o 0
0 1 2 3 4 5 6 7 8 9
data
End of String
Symbol

Strings
 Each character has an integer representation
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a b c d e z…………
97 98 99 100 101 ………………………112
A B C D E Z…………
65 66 67 68 69 ……………………… 90
0 1 2 3 4 98765
48 49 50 51 52 53 54 55 56 57
0
0
n
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Strings
 Characters can be interpreted as integers
char c = ‘A’;
printf(“%c n”,c);
prints A
printf(“%d n”,c);
prints 65
Printf(“%c n”,65);
prints A
16

Array

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