.. _arrays_intro:

Arrays
======

- 
   An *array* is a sequence of data items that are of the same type
   and stored contiguously in memory.

- 
   Arrays can be one dimensional (single sequence of data), two, three,
   or N dimensional. Regardless of how the data is indexed (to fit
   the needs of the program design) it is all stored sequentially.

- 
   The index of the array always goes from 0  to N - 1, where the
   size of the array is N.

- 
   Square brackets, [size], are used to initialize an array. The size
   of the array is an integer constant, either a number or a #define
   constant.

- 
   A variable or expression may be used as an array index when
   referencing an array, but not when declaring it.

- 
   Automatic (on the stack) arrays are not initialized by default. It
   is best to never assume an initial value of an array.

- 
   To initialize an array, put the values in brackets.

::

    int a[3] = {3,4,5};
    int a[] = {3,4,5};      /* size determined by the initial brackets */
    int b[][3] = {{7,8,9},{4,5,6},{3,4,5}}; /* a 3x3 array */

An Array Example
----------------

::

    #include <stdio.h>
    #define  N 5
    
    int main(void)
    {
        int a[N], i, sum=0;
    
        for( i=0; i < N; i++ ) {
            a[i] = 7 * i * i;
            sum += a[i];
            printf( "a[%d] = %d\t", i, a[i] );
        }
        return 0;
    }