1. Arrays
An array is a grouping of elements of the same type that share a common base name
Can have any number of elements in the array
Individual elements are accessed using the base name with a numerical (integer) subscript
Subscript numbering starts at zero
Ends at N-1 where N is the number of elements in the array
Array elements are stored in sequential memory locations

2. Declaring an Array Syntax: type arrayName[size];
type can be any valid C++ type
Ex: int, float, double, char, string, …
arrayName can be any valid C++ variable name
size can be any positive integer (i.e. greater than zero)
Specifies the number of elements in the array

3. Example Declarations int scores[10]; float salaries[25];
An array of 10 integers
float salaries[25];
An array of 25 floating point numbers
string names[4];
An array of 4 string variables

4. Accessing array elements
Array elements are accessed using the subscript operator
Square brackets [num]
Num: an integer between 0 and N-1, where N is the number of elements
Error if num is less than zero or greater than or equal to N
// an array of 10 integers
int scores[10];
scores[0] is the first element of array
scores[4] is the fifth element of array
scores[9] is the last element of array

5. Working with array elements
Individual array elements are variables
They can be used the same way simple variables are
Examples:
int scores[10]; string names[4];
scores[0] = 80; names[1] = “Bob”;
int sum= scores[5] + scores [6]; cout << “hello “ << names[1] << endl;
if(scores[3] > scores[4]) {
cout << “yes!” << endl; }

6. Sequential vs. Random access
Access any element at any time using a valid subscript number
Sequential access
Access in numerical order
Example:
int square[8];
for (int i = 0; i < 8; i++) {
square[i] = i * i;
} (stored in sequential memory locations)
[0]
[1]
[2]
[3]
[4]
[5]
[6]
[7] 1 4 9 16 25 36 49

7. Array Initialization Case 1:
type arrayName[N] = { val0, val1, …, val(N-1) };
Specify N initial values
If fewer than N are given, unspecified values are uninitialized (random values)
Case 2:
type arrayName[] = { val0, val1, …, val(N-1) };
Size not specified – array automatically becomes size of initialization list
Example
float cube[5]= { 0.0, 1.0, 8.0, 27.0, 64.0 };
[0]
[1]
[2]
[3]
[4]
0.0
1.0
8.0
27.0
64.0

8. Passing Arrays to Functions
Arrays are always passed by reference (actually by pointer)
Which means the elements can be changed by the function
Pass entire array to a function by writing just its name (no subscripts or brackets) in the argument list of the function call
In function definition and prototype, use empty brackets ([ ]) to indicate an array

9. Passing Arrays to Functions (example)
// function definition
void func(int A[], int size) {
if(size >= 3) A[2]= 10; }
// prototype void func(int[], int); main() { int array[3]= { 2, 4, 6 }; // call the function func(array, 3); cout << array[2] << endl; }
This will output “10”

10. More on passing arrays
Use keyword const to indicate that array argument cannot be changed by function
Compiler will not allow changes to arrays passed with a const prefix
This will not compile
// function definition
void func(const int A[], int size) {
if(size >= 3) A[2]= 10; // error: attempting to change a value in a const array }

11. Individual elements are passed by value
Individual elements are treated like any other variable
Individual elements are passed by value
// function definition
void func(int a) {
a=3; }
Neither func(x) or func(array[2]) will change the value passed in
i.e. both x and array[2] will retain their original values after the “func()” is finished its execution

12. Parallel Arrays
Parallel arrays: a set of arrays that store related information in separate arrays, but with the same index number
permits storage of multiple pieces of information for a collection of items
For Example:
string name[4]= { "John", "Mary", "Lucy", "George" };
string gender[4]= { "male", "female", "female", "male" };
int age[4]= { 20, 21, 19, 23 };
Information about Mary is stored in each array at index 1…

13. Parallel Array Use
// find the oldest
int oldest=age[0], indx=0;
for (int i=1; i<4; i++) {
if(age[i] > oldest) {
oldest= age[i];
indx=i; }
cout << name[indx] << “is oldest”;
string name[4]= { "John", "Mary", "Lucy", "George" }; string gender[4]= { "male", "female", "female", "male" }; int age[4]= { 20, 21, 19, 23 };

14. Multidimensional Arrays
Arrays can have more than one dimension
Example: 2D array
Commonly used to represent a table
char ticTacToe[3][3];
Access
ticTacTie[1][2]
Note: The total number of elements is just the product of the sizes of each dimension:
int array[3][5];
Number of elements is 15 (3*5)

15. Accessing a Multidimensional Array
Indexing starts at zero (like a 1D array)

16. Initialization
Each inner pair of braces contains initial values for one row of the array matrix
const int NUM_ROWS = 2;
const int NUM_COLS = 3;
float matrix[NUM_ROWS][NUM_COLS] = {
{5.0, 4.5, 3.0},
{-16.0, -5.9, 0.0} };

17. Strings and Arrays of Characters
string object uses an array of char
Can reference individual character of a string object in different ways
name[ i ]
name.at( i )
A useful member function of string class
name.length()