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

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

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

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

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; }

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

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 };

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

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);

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 }, s=3; // call the function func(array, s); cout << array[2] << endl; } This will output “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; }

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

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]

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

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} };

Implicit Declaration Row dimension can be anonymous, but column dimension must be specified float matrix[][2] = {{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

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

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

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()