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Array Data Structures
1. Array
A Linear Data Structure
SONI GUPTA
ASSISTANT PROFESSOR (NPIU-TEQIP III )
HBTU KANPUR, UP
TEQIP
-III
2. Topics to be covered
What is an array?
Declaration of an array
Initialization of an array
Examples
Representation of an array in memory
Pointers and array
2-dimensional array
Representation in row major order and column major order
Example: Representation of Lower triangular matrix
Example: Representation of tri diagonal matrix
Example: Representation of X-matrix
Disadvantage
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3. Array
Array is a collection of similar elements having same data type, accessed using a
common name.
The elements of an array occupy contiguous memory locations.
100 104 108 112 116 120
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4. Dimension of an array:
In C language there is no limitation on the dimension on an array
1-Dimensional
• List
• Vector
2-dimensional
• Table
• Matrix
3-dimensional
• 3-d matrix
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5. Declaration of an array
Type-name variable-name [size];
The array is indexed from 0 to size-1
The size (in brackets) must be an integer literal or a constant variable.)
Based on the size declared the compiler determine how much space to allocate in
memory.
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6. Examples:
int list[5]; // an array of 5 integers
list
list[0]=4, list[1]=6, list[2]=1, list[4]=50
char name[5]; // an array of 5 characters
name
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4 6 1 100 50
a i o u e
7. int table[2][3]; // a two dimensional array of integers
table
table[0][0]=5, table[0][1]=9, table[1][2]=5,
Int location[5][5][10]: // a three dimensional array of integer
Int *a[4] // an array of pointer/address
a
5 9 14
1 3 5
1004 1008 1120 1222
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8. Initializing an Array
int list[5]={1,2,5,6,1};
char [20]={a,r,w,q,q,t}; // all uninitialized values will set to zero.
int table[2][3]={{2,3,8}{3,4,9}};
int count[ 100 ] = { 1, 2, 3, [10] = 10, 11, 12, [60] = 50, [42] = 500 };
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9. Representation of an array in memory
0 1000 (Base address)
1 1004
2 1008
3 1012
4 1016
IndexValues Address (in Byte)
4
6
1
100
50
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10. Pointers and Array
An array variable is actually a pointer which hold the address of the first element
of the array.
We can access array value by array notations or pointer value.
a[0]=*a
a[1]=*(a+1)
a[2]=*(a+2)
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11. a = a+0 = &a[0]
a+1 = &a[1]
a+i = &a[i]
&(*(a+i)) = &a[i] = a+i
*(&a[i]) = *(a+i) = a[i]
Address of an element i of array a = a + i * sizeof(element)
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12. 2-dimensional Array
Suppose a 2-d array A[i][j];
Row major order
Location of A[i][j] = A + ( Number of rows * i + j )*sizeof(element)
For Column Major Order
Location of A[i][j] = A + ( Number of Columns * j + i )*sizeof(element)
A[i][j]= *(*(A + i) + j)= *(A[i] + j) = (*(A+i))[j]
&A[i][j]= *(A + i) + j = A[i] + j
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16. Column major order
for (j=1,j<=3,j++)
for (i=1,i<=3,i++)
{
Printf(“Enter the element”);
Scanf(“%d”,A[i][j]);
}
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17. Row major order
for (i=1,i<=3,i++)
for (j=1,j<=3,j++)
{
Printf(“Enter the element”);
Scanf(“%d”,A[i][j]);
}
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18. Character Strings as Arrays of Characters
Strings are stored in an array of character (char) type along with the null
terminating character "0" at the end
char name[ ] = { ‘I', ‘N', ‘D',‘I', ‘A', 'O'};
OR char name[ ] = “INDIA";
'0' is not necessary. C inserts the null character automatically.
length of string= 5
size of string=6
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29. Disadvantage
The number of element must be known in advance.
Array is static in nature i.e array size is fixed and it is allocated at compile time. The
memory which is allocated to array can not be increased or decreased.
If we will allocate memory more than required then space will be wasted.
The elements of an array are stored in consecutive memory locations. Therefore
insertion and deletion is difficult and time consuming.
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Editor's Notes
Array variables are declared identically to variables of their data type, except that the variable name is followed by one pair of square [ ] brackets for each dimension of the array.
Space is allocated only once, at the time the array is declared. The array does NOT change sizes later if the variable used to declare it changes.
We can declare an array as we declare a variable. Simply list the array values in set notation { } after the declaration
If an array is to be completely initialized, the dimension of the array is not required. The compiler will automatically size the array to fit the initialized data.
If the size of the array is not given, then the largest initialized position determines the size of the array.
