Easy C++


C++ Tutorial - Lesson 10: Arrays and Vectors

Defining Arrays

by John Kopp

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Defining Arrays
Welcome to About.com's C++ tutorial. This lesson introduces arrays and vectors. Arrays are a data structure that is used to store a group of objects of the same type sequentially in memory. They are a built-in part of the C++ language. All the elements of an array must be the same data type, for example float, char, int, pointer to float, pointer to int, a class, structure or function. Functions provide a way to define a new operation. They are used to calculate a result or update parameters. Functions will be covered in a later lesson. The elements of an array are stored sequentially in memory. This allows convenient and powerful manipulation of array elements using pointers. The use of arrays is common in C and C++ coding and is important to understand well.

Vector is a container class from the C++ standard library. As is true for an array, it can hold objects of various types. Vector will also resize, shrink or grow, as elements are added. The standard library provides access to vectors via iterators, or subscripting. Iterators are classes that are abstractions of pointers. They provide access to vectors using pointer-like syntax but have other useful methods as well. The use of vectors and iterators is preferred to arrays and pointers. Common bugs involving accessing past the bounds of an array are avoided. Additionally, the C++ standard library includes generic algorithms that can be applied to vectors and to other container classes.

Defining Arrays
An array is defined with this syntax.

datatype arrayName[size];


int ID[30];
              /* Could be used to store the ID numbers of students in a class */

float temperatures[31];
              /* Could be used to store the daily temperatures in a month */

char name[20];
              /* Could be used to store a character string. C-style character strings are terminated be the null character, '\0'. This will be discussed in a later lesson. */

int *ptrs[10];
              /* An array holding 10 pointers to integer data */

unsigned short int[52];
              /* Holds 52 unsigned short integer values */

class POINT {
    POINT() { x = 0; y = 0;}
    //Accessor methods declared here
    int x;
    int y;

POINT dots[100];

This last example declared an array of objects of class POINT. A class to be used in an array must have a default constructor, that is, a constructor without arguments. The compiler uses this constructor when allocating space for the array when it is defined.

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