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 are used and treated the same way any other variable is!
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 in declaration – array automatically becomes size of initialization list
Example
float cube[5]= { 0.0, 1.0, 8.0, 27.0, 64.0 };

8. Array Storage Array elements are stored in sequential memory locations
Example:
float cube[5]= { 0.0, 1.0, 8.0, 27.0, 64.0 };
(note: float type uses 32bits/4 bytes)
Cube[5]
Memory address
Array index
Value
0x1000
[0]
0.0
0x1004
[1]
1.0
0x1008
[2]
8.0
0x1012
[3]
27.0
0x1016
[4]
64.0

9. 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
Ex: func(array, 3);
In both the function definition and prototype, use empty brackets ([ ]) to indicate an array
Ex: void func(int A[], int size);

10. 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”

11. 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; }

12. Individual elements are passed by value
Individual elements are treated like any other variable
They 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

13. 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]

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

15. 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} };

16. Implicit Declaration
Row dimension can be anonymous, but column dimension must be specified
float matrix[][NUM_COLS] = {{5.0, 4.5, 3.0}, {-16.0, -5.9, 0.0}};
-> C++ must know the number of elements in each row in order to access a particular array element
This can be used in function prototyping and definition

17. Function sumMatrix float sumMatrix (float table[][NUM_COLS], int rows){
float sum = 0.0;
// Add each array element value to sum.
for (int r = 0; r < rows; r++)
for (int c = 0; c < NUM_COLS; c++)
sum += table[r][c];
return sum; }
* Note: NUM_COLS is global

18. Arrays with Several Dimensions
const int PEOPLE = 10;
const int YEARS = 5;
money sales[PEOPLE][YEARS][12];

19. 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()