2.11. 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 */

2.11.1. 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;
}