Arrays

Part 9 dbg

Arrays

• An array is a fixed number of contiguous memory locations, all containing data of the same type, identified by one variable name.

• Refer to a particular location by specifying the name of the array and the index (position number) of the location.

• Index positions of arrays start at 0.• Values stored at the positions are called items or

elements.

Declare and Allocate an Array in C#

• Declare the array: //assigns name

int[ ] scores;

• Allocate memory for the array:scores = new int[10]; //room for 10 integers

• Declare and allocate in one step:int[ ] scores = new int[10]; //all in 1 step;

assigns //default value for data type to all elements

Initialize an Array

• Space for an array can be automatically allocated by initializing the array with a set of values

• string[ ] weekDays = new string [ ] {″Monday″, ″Tuesday″, ″Wednesday″, ″Thursday″, ″Friday″};

- or -

• string[ ] weekDays = {″Monday″, ″Tuesday″, ″Wednesday″, ″Thursday″, ″Friday″};

• Note that this initialization creates an array just big enough to contain the set of assigned values

Declaring and Initializing 1-Dimensional Arrays in C# vs. C++ and JavaC++: int scores[SIZE]; //just declare name and set aside

//memory for SIZE elements int scores[SIZE] = {num1 … numn}; //initialize

int scores[ ] = {num1…numn}; //initialize

Java and C#: int[ ]scores; //just declare; memory is not set aside yet

int[ ] scores = new int[SIZE]; //declare and // initialize with default values for

datatype

int[ ] scores = new int[] {num1…numn}; //declare and initialize

int[ ] scores = {num1…numn}; //declare and //initialize

Let’s Try Some Exercises

• Declare an array named homeruns that will hold the number of homeruns scored by a particular team in each of the 162 games of the season.

• Declare an array named prices that will store the following product prices: 12.99, 25.00, 3.75, 8.23, 0.97, 59.98

Assign a Value to an Array Element

• Given an array, temps, of type integer, assign a value to first element of array:

Extract an Element Value from an Array

• Given an array, temps, of type integer, store the third element value in a variable:

Filling/Printing Array Values

• Arrays are handy containers for data generated by a loop.

• In this example, values are generated by a loop and stored in an array.

• The values are then printed to the output window as they are extracted from the array using a second loop.

DataToArray

foreach loop

• A foreach loop is similar to a for loop, but you do not have to worry about the index variable; the foreach loop will automatically iterate though all elements of the array.

• You will need some variable to store the array element value extracted in each iteration of the loop.

• Syntax:

foreach(data-type someVariable in arrayName)

Foreach

11

foreach Example

int sum = 0;

int[ ] grades = new int [10] {81, 69, 93, 100, 90, 82, 70, 94, 88, 95};

foreach(int grade in grades)

{

sum = sum + grade; //adds array element // value to sum

variable

}

Strings and Arrays of Type Char

• A string is a data type designed to contain text.• A string has a Length property which holds the

number of characters in a string.• A string may be converted to an array of type

char using the ToCharArray() method of the string type.

• An array has a GetUpperBound() method which returns the highest index in an array.

StringToChars

Multiple Dimension Arrays

• An array with one dimension is a list.• An array with two dimensions is a table.• Adding a second dimension means that each

position in the first dimension now behaves like a row in a table that has several columns.

• The sizes of the dimensions of an array are separated by commas in the declaration/allocation bracket.

Declaring and Initializing 2-Dimensional Arrays in C++ and JavaC++:

int scores[ROWS][COLS]; //just declare name and set // aside memory

int scores[SIZE] [COLS] = {num1 … numn}; //initialize with values

int scores[ ] [COLS] = {num1…numn}; //initialize w values

Java: int[ ][ ]scores; //just declare name; memory not set aside yet

int[ ][ ] scores = new int[ROWS][COLS]; // sets aside memory for array elements

int[ ][ ] scores = {{row0col0, … row0coln},{row1col0, … row1coln},{row2col0, … row2coln}}; //initialize w

values

Declare and Initialize a Two-dimensional Array in C#

decimal [ , ] postalRates; //declares name only

decimal [ , ] = new decimal [2,6]; //initializes array with //default value for datatype

decimal[,] postalRates = new decimal[2,6] {{4.50, 5.00, 5.50, 6.50, 7.50, 9.00}, {9.99, 11.25, 11.99, 14.99, 16.99, 20.00}}; //initialize w values

Zone 1 [0]

Zone 2 [1]

Zone 3 [2]

Zone 4 [3]

Zone 5 [4]

Zone 6 [5]

Regular [0] 4.50 5.00 5.50 6.50 7.50 9.00

Priority [1]9.99 11.25 11.99 14.99 16.99 20.00

Let’s Try Some Exercises

• We want an array named grades that will store 3 exam grades (in columns) for each of 5 students (in rows).

• Make up the exam grades.

Array Bounds• You can determine the UpperBound of an array

with the array’s GetUpperBound() method, which returns index of the last element in the array.

• Call GetUpperBound() with a 0 parameter for 1st dimension of array; with a 1 for upper bound of 2nd-dimension of a multi-dimensioned array.

• There is a Length property for a one-dim array and there is a GetLength() method with a 0 parameter will return the number of elements for 1st dimension of array; with a 1 for upper bound of 2nd-dimension of a multi-dimensioned array.

18

Arrays

• C# will throw an Exception, if you attempt to use an index that is “out of range” for an array. This did not happen in C++ (the programmer had to be careful) but does happen in Java as well.

Compound Data Types

Structs

New Data Types

• So far we have used only the primitive data types such as int, string, bool, and double.

• C# also provides for the definition of structs, or compound data types.

• We can think of a struct as being a package of variables of different data types.

Structs• The different variables

within the definition of a struct are analogous to the fields of a database record.

• We might define a struct called person that could store several attributes to define a human.

• Use the public keyword to declare fields.

StructData

An Array of Structs

• We can construct a simple table of data by creating an array where each element is a struct.

• Declare an array of structs:Person[ ] faculty = new Person[10];

StructArray

first middle last age sex

Person[0] Dee B Gudmundsen 29 F

Person[1] Michael Kuhrt 49 M

Person[2] John P Avitabile 39 M

Load EventUse with Form

Event “Fires” Immediately before the form displays for the first time.

Example You want to set some values (perhaps a timestamp) via code before the form appears. You might want to fill a ListBox with items, or fill an array with values via code before the form displays.

private void frmOrder_Load(object sender, System.EventArgs e)

{

// store current time in a variable

DateTime currentTime = DateTime.Now;

//display current time as hh:mm:ss AM/PM

lblTransactionDate.Text = currentTime.ToString(“T”);

}