Arrays

Introduction

Most programming languages offer the array data structure as a basic language element.

Arrays are often used to implement other data structures, such as queues, stacks, lists and hash tables.

An array (in C) is a collection of individual data elements that is:

Ordered -- we can count off the elements 0,1,2,3,...
Fixed in size
Homogeneous -- all of the elements have to be of the same type, e.g., int, float, char, etc.

In C, each array has two fundamental properties:

the element type
the size

Declaring Arrays

The general form of an array declarations:


     elementtype arrayname [ arraysize ] ;

Examples of array declarations:

int array [10];
int rolls [HIGH + 1];
double scores [ENROLLMENT];

What happens in memory ?

The array declaration: int sample [5]; would cause space to be allocated that is big enough to hold 5 ints contiguously, as shown:

sample

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sample
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Accessing array elements

We can select a particular array element by giving it's index .

In C, the elements of an array with N elements are indexed by the integers 0, 1, 2, 3, ... (N-1).

sample

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sample
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The general form then:


     arrayname [ indexValue ]

Examples: sample [2] = 25; would cause the element at index 2 to be assigned the value 25

sample

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sample
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The following code:


/* Initialization of all of the 
elements of the array to 0 */
for (i = 0; i < 5; i++)
{
   sample [i] = 0;
}

would cause all of the elements of the array to be set to 0

sample

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sample
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Multi-dimensional Arrays

If data elements of an array are arrays themselves, it is called a multidimensional array.

Although a two-dimensional array is really an array of arrays, it is more typical to think of it as a two dimensional table.

Multidimensional arrays are also commonly used. Up to three subscripts is not unusual. ANSI C requires that an implementation allow multidimensional arrays of at least six dimensions.

Uses of Arrays

The simple uses of arrays include anything where many values of the same data type need to be kept for a particular purpose. Vectors in physics, matrices in linear algebra, tabular data, two-dimensional images or three dimensional models.