Amu_Ke_Fundye

Arrays

• Array is a collection of similar elements having same data type, accessed using a common name.
• Array elements occupy contiguous memory locations.
• Array indices start at zero in C, and go to one less than the size of the array.

Declaration of an Array:

type variable[num_elements];

Example: int A[100];

• It creates an array A with 100 integer elements.
• The size of an array A can’t be changed.
• The number between the brackets must be a constant.

Initialization of an Array:

• int A[5]= {1,2,3,4,5}; /*Array can be initialized during declaration*/
• int A[5]={1,2,3}; /* Remaining elements are automatically initialized to zero*/
• int A[5]={1,[1]=2, 3,4,[4]=0};/* Array element can be initialized by specifying its index location*/

Problems with Arrays:

• There is no checking at run-time or compile-time to see whether reference is within array bounds.
• Size of array must be known at compile time.

Example-1: Read the 10 values into an array of size 10.

void main()
{
int A[10], i;
for (i=0; i<10; i++)
{
printf(“Enter the number %d”, i+1);
scanf(“%d”, &a[i]);
}

Example-2: Print the 10 values of an Array A.

void main()
{
int A[10], i;
for (i=0; i<10; i++)
{
printf(“%d “, A[i]);
}
}

Pointers & Arrays: Let a[10] be an array with 10 elements.

• The name a of the array is a constant expression, whose value is the address of the 0th location.
• An array variable is actually just a pointer to the first element in the array.
• You can access array elements using array notation or pointers.
• a[0] is the same as *a
• a[1] is the same as *(a + 1)
• a[2] is the same as *(a + 2)
• 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)

Multi-Dimensional Array

In C language, one can have arrays of any dimensions. Let us consider a 3 × 3 matrix

3 × 3 matrix for multi-dimensional array

To access the particular element from the array, we have to use two subscripts; one for row number and other for column number. The notation is of the form a [i] [j], where i stands for row subscripts and j stands for column subscripts.

We can also define and initialize the array as follows

Note: Two Dimensional Array b[i][j]

• For Row Major Order: Size of b[i][j] = b + ( Number of rows * i + j )*sizeof(element)
• For Column Major Order: Size of b[i][j] = b + ( Number of Columns * j + i )*sizeof(element)
• *(*(b + i) + j) is equivalent to b[i][j]
• *(b + i) + j is equivalent to &b[i][j]
• *(b[i] + j) is equivalent to b[i][j]
• • b[i] + j is equivalent to &b[i][j]
• (*(b+i))[j] is equivalent to b[i][j]

Strings

In C language, strings are stored in an array of character (char) type along with the null terminating character “\0″ at the end.

Printf and scanf use “%s” format character for string. Printf print characters up to terminating zero. Scanf read characters until whitespace, store result in string, and terminate with zero.

Example:

char name[ ] = { ‘G’, ‘A’, ‘T’,’E’, ‘T’, ‘O’, ‘P’, ‘\O’};

OR
char name[ ] = “GATETOP”;

• ‘\0′ = Null character whose ASCII value is O.
•  ‘0’ = ASCII value is 48.
• In the above declaration ‘\0′ is not necessary. C inserts the null character automatically.

•  %s is used in printf ( ) as a format specification for printing out a string.
• All the following notations refer to the same element:  name [i] ,  * (name + i),  * (i + name),  i [name]

Regards 

Amrut Jagdish Gupta