Chp 7 - Arrays and Vectors

Array

A variable that can store multiple values of the same type

• values are stored in adjacent memory locations

• declared using [ ] operator

  • int tests[5];

• the size of an array is the total number of bytes allocated for it: (number of elements) * (size of each element)

Accessing Array Elements

each element in an array is assigned a unique subscript (starting at 0 to n - 1)

• array elements can be used as regular variables

• arrays must be accessed via individual elements

• can access element with a constant or literal subscript

• can use integer expression as subscript

Using a Loop to Step Through an Array

Array Initialization

• global array ➡ all elements initialized to 0 by default

• local array ➡ all elements uninitialized by default

• arrays can be initialized with an initialization list

  • int tests[5] = {79, 82, 91, 77, 84};

  • you can also determine the array size by the size of the initialization list

No Bounds Checking in C++

• when you use a value as an array subscript, C++ does not check it to make sure it is a valid subscript

• you can use subscripts beyond the bounds of the array, doing so can corrupt other memory locations, crash program, lock up computer, cause elusive bugs…BE CAREFUL!

The Range-Based for Loop

• C++ 11

• a loop that iterates once for each element in an array

• each time the loop iterates, it copies an element from the array to a built-in variable, known as the range variable

• the range-based for loop automatically knows the number of elements in an array, you do not have to:

  • use a counter variable

  • worry about stepping outside the bounds of the array

• can be used in any situation where you do not need to use the element subscripts

Copying one array to another

assign element-by-element

Printing an array

print element-by-element

Structured Binding Declarations

defines a set of variables and initializes them with the values that are stored in an array

• auto [variable1, variable2, etc…] = array;

Parallel Arrays

two or more arrays that contain related data

• a subscript is used to relate arrays (elements at the same subscript are related)

• arrays may be of different types

Arrays as Function Arguments

• to pass an array to a function, use the array name

  • showScores(tests);

• to define a function that takes an array parameter, use empty [] for array argument

  • void showScores(int []);

• it is common to pass array size so that the function knows how many elements to process

  • showScores(tests, ARRAY_SIZE);

• array size must be reflected in prototype header

Two-Dimensional Arrays

• First declarator is number of rows, second is number of columns.

  • const int ROWS = 4, COLS = 3;

  • int exams[ROWS][COLS]

• initialized row-by-row

• some values in a row will be set to 0 or NULL

• in a parameter

  • void getExams(int exams[][COLS], int rows)

Arrays with 3+ Dimensions

• you can define arrays with any number of dimensions

• when used as a parameter, specify all but 1st dimension in prototype heading

  • void getRectSolid(short [][3][5])

STL vector

• A data type defined in the Standard Template Library

• can hold values of any type

• automatically adds space as more is needed - no need to determine size at definition

• can use [ ] to access elemets 

Declaring Vectors

• #include<vector>

• declare a vector to hold int element:

  • vector<int> scores;

• declare a vector with initial size 30 (only starting size)

  • vector<int> scores(30);

• declare a vector and initialize all elements to 0

  • vector<int> scores(30, 0);

• declare a vector initialized to size and contents of another vector

  • vector<int> finals(scores);

adding elements to a vector

• you can initialize a vector with a list of values (C++ 11)

  • vector<int> numbers {10, 20, 30, 40};

• use push_back member function to add element to a full array or to an array that had no defined size:

  • scores.push_back(75);

• use size member function to determine size of a vector

  • howbig = score.size();

removing vector elements

• use pop_back member function to remove last element from vector

  • scores.pop_back();

• to remove all contents of vector. use clear member function

  • scores.clear();

• to determine if vector is empty, use empty member function

  • while (!scores.empty())

Range-Based for Loop with a vector

Other Useful Member Functions