7.1. Introduction

This chapter introduces the important topic of data structures—collections of related data items. Arrays are data structures consisting of related data items of the same type. We considered classes in Chapter 3. In Chapter 19, Bits, Characters, C Strings and structs, we discuss the notion of structures. Structures and classes can each hold related data items of possibly different types. Arrays, structures and classes are "static" entities in that they remain the same size throughout program execution. (They may, of course, be of automatic storage class and hence be created and destroyed each time the blocks in which they are defined are entered and exited.)

After discussing how arrays are declared, created and initialized, we present a series of practical examples that demonstrate several common array manipulations. We then explain how character strings (represented until now by string objects) can also be represented by character arrays. We present an example of searching arrays to find particular elements. The chapter also introduces one of the most important computing applications—sorting data (i.e., putting the data in some particular order). Two sections of the chapter enhance the case study of class GradeBook in Chapters 3–6. In particular, we use arrays to enable the class to maintain a set of grades in memory and analyze student grades from multiple exams in a semester—two capabilities that were absent from previous versions of the GradeBook class. These and other chapter examples demonstrate the ways in which arrays allow programmers to organize and manipulate data.

The style of arrays we use throughout most of this chapter are C-style pointer-based arrays. (We'll study pointers in Chapter 8.) In the final section of this chapter, and in Chapter 20, Standard Template Library (STL), we'll cover arrays as full-fledged objects called vectors. We'll discover that these object-based arrays are safer and more versatile than the C-style, pointer-based arrays we discuss in the early part of this chapter.