ARRAYS
Little Boxes on the hillside
Arrays are a data structure which hold multiple variables of the same data type. Consider the case where a programmer needs to keep track of a number of people within an organisation. So far, our initial attempt will be to create a specific variable for each user. This might look like,

int name1 = 101;
int name2 = 232;
int name3 = 231;

It becomes increasingly more difficult to keep track of this as the number of variables increase. Arrays offer a solution to this problem.
An array is a multi-element box, a bit like a filing cabinet, and uses an indexing system to find each variable stored within it. In C, indexing starts at zero.
Arrays, like other variables in C, must be declared before they can be used.
The replacement of the above example using arrays looks like,

int names[4];
names[0] = 101;
names[1] = 232;
names[2] = 231;
names[3] = 0;

We created an array called names, which has space for four integer variables. You may also see that we stored 0 in the last space of the array. This is a common technique used by C programmers to signify the end of an array.
Arrays have the following syntax, using square brackets to access each indexed value (called an element).

x[i]
so that x[5] refers to the sixth element in an array called x. In C, array elements start with 0. Assigning values to array elements is done by,

x[10] = g;
and assigning array elements to a variable is done by,

g = x[10];
In the following example, a character based array named word is declared, and each element is assigned a character. The last element is filled with a zero value, to signify the end of the character string (in C, there is no string type, so character based arrays are used to hold strings). A printf statement is then used to print out all elements of the array.
/* Introducing array's, 2 */
#include <stdio.h>

main()
{
char word[20];

word[0] = 'H';
word[1] = 'e';
word[2] = 'l';
word[3] = 'l';
word[4] = 'o';
word[5] = 0;
printf("The contents of word[] is -->%s\n", word );
}

Sample Program Output
The contents of word[] is Hello

DECLARING ARRAYS
Arrays may consist of any of the valid data types. Arrays are declared along with all other variables in the declaration section of the program.

/* Introducing array's */
#include <stdio.h>

main()
{
int numbers[100];
float averages[20];

numbers[2] = 10;
--numbers[2];
printf("The 3rd element of array numbers is %d\n", numbers[2]);
}

Sample Program Output
The 3rd element of array numbers is 9

The above program declares two arrays, assigns 10 to the value of the 3rd element of array numbers, decrements this value ( --numbers[2] ), and finally prints the value. The number of elements that each array is to have is included inside the square brackets.

#include <stdio.h>
main()
{
int x;
static int values[] = { 1,2,3,4,5,6,7,8,9 };
static char word[] = { 'H','e','l','l','o' };
for( x = 0; x < 9; ++x )
printf("Values [%d] is %d\n", x, values[x]);
}

Sample Program Output
Values[0] is 1
Values[1] is 2
....
Values[8] is 9

The previous program declares two arrays, values and word. Note that inside the squarebrackets there is no variable to indicate how big the array is to be. In this case, C initializes the array to the number of elements that appear within the initialize braces. So values consist of 9 elements (numbered 0 to 8) and the char array word has 5 elements.

The following program shows how to initialise all the elements of an integer based array to the value 10, using a for loop to cycle through each element in turn.

#include <stdio.h>
main()
{
int count;
int values[100];
for( count = 0; count < 100; count++ )
values[count] = 10;
}