1. Arrays Part 9 dbg

2. 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.

3. 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

4. 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

5. Declaring and Initializing 1-Dimensional Arrays in C# vs. C++ and Java C++: 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

6. 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

7. Assign a Value to an Array Element Given an array, temps, of type integer, assign a value to first element of array:

8. Extract an Element Value from an Array Given an array, temps, of type integer, store the third element value in a variable:

9. 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

10. 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. 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 }

12. 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

13. 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.

14. Declaring and Initializing 2-Dimensional Arrays in C++ and Java C++: 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

15. 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] 4.505.005.506.507.509.00 Priority [1] 9.9911.2511.9914.9916.9920.00

16. 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.

17. 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 1 st dimension of array; with a 1 for upper bound of 2 nd -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 1 st dimension of array; with a 1 for upper bound of 2 nd -dimension of a multi-dimensioned array.

18. 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.

19. Compound Data Types Structs

20. 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.

21. 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

22. 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 firstmiddlelastagesex Person[0] DeeBGudmundsen29F Person[1] MichaelKuhrt49M Person[2] JohnPAvitabile39M

23. Load Event Use 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”); }