UMBC CS 201, Fall 06
 UMBC CMSC 201 Fall '06 CSEE | 201 | 201 F'06 | lectures | news | help Search Notes:

# 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 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:

 FE09

## 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).

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0 1 2 3 4
The general form then:
```
arrayname [ indexValue ]

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

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 25
0 1 2 3 4
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

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 0 0 0 0 0
0 1 2 3 4

## 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, or anything that can be thought of as a "table".

CSEE | 201 | 201 F'06 | lectures | news | help

Tuesday, 22-Aug-2006 07:13:55 EDT