EEC-693/793 Applied Computer Vision with Depth Cameras Lecture 6 C# Primer II Wenbing Zhao wenbing@ieee.org 1

Outline C# primer II Based on C# in a nutshell book: http://shop.oreilly.com/product/9780596001810.do C# Programming Guide http://msdn.microsoft.com/en-us/library/67ef8sbd.aspx

Array To use arrays Array: store a list of things type [*] array-name = [ new type [ dimension+ ][*]*; | { value1, value2, ... };] [*] is the set: [] [,] [, ,] ... Array size defined this way is static System.Collection provides dynamic arrays To use arrays Declaring arrays Initializing arrays Accessing array members

Types of Arrays Single dimensional array Multidimensional array Declaring single dimensional array: int[] numbers; Declaring does not create an array, to create one: int[] numbers = new int[5]; Multidimensional array string[,] names; string[,] names = new string[5,4]; Jagged array (array of arrays) byte[][] scores;

Jagged Arrays and More Creating a jagged array: mixed arrays byte[][] scores = new byte[5][]; for (int x = 0; x < scores.Length; x++) { scores[x] = new byte[4]; } mixed arrays int[][,,][,] numbers;

Arrays: An Example App // arrays.cs using System; class DeclareArraysSample { public static void Main() { int[] numbers = new int[5]; // Single-dimensional array string[,] names = new string[5,4]; // Multidimensional array byte[][] scores = new byte[5][]; // Array-of-arrays (jagged array) // Create the jagged array for (int i = 0; i < scores.Length; i++) { scores[i] = new byte[i+3]; } // Print length of each row Console.WriteLine("Length of row {0} is {1}", i, scores[i].Length); } } Example Program#5

Challenge Task for Arrays Write a program to sort number of elements in an array using a one-dimensional array. The input of elements should be taken during run time int[] ele ; int num, i, j; Console.WriteLine("Enter number of Elements"); num = int.Parse(Console.ReadLine()); ele = new int[num]; Console.WriteLine("Enter " + num + " elements to be sorted"); for (i = 0; i < num; i++) { ele[i] = int.Parse(Console.ReadLine()); } 11/14/2018 EEC492/693/793 - iPhone Application Development

Variable and Parameters A variable represents a typed storage location A variable can be a local variable, parameter, array element, an instance field, or a static field All variables have an associated type Defines the possible values the variable can have and the operations that can be performed on that variable All variables must be assigned a value before they are used A variable is either explicitly assigned a value or automatically assigned a default value. Automatic assignment occurs for static fields, class instance fields, and array elements not explicitly assigned a value (default init value typically is 0 or null)

Array Element Initialization When any type of array is created, each of the elements is automatically initialized to the default value for the type The default values for the predefined types are 0 for integer types 0.0 for floating point types false for Booleans, and null for reference types 11/14/2018 EEC492/693/793 - iPhone Application Development

Variable and Parameters: Example using System; class Test { int v; // Constructors that initalize an instance of a Test public Test() {} // v will be automatically assigned to 0 public Test(int a) { // explicitly assign v a value v = a; } static void Main() { Test[] tests = new Test [2]; // declare array Console.WriteLine(tests[1]); // ok, elements assigned to null Test t; Console.WriteLine(t); // error, t not assigned before use } Example Program#6

Parameters A method typically has a sequence of parameters Parameters define the set of arguments that must be provided for that method static void Foo(int p) {++p;} static void Main() { Foo(8);} By default, arguments are passed by value: a copy is made May pass by reference by using the “ref” keyword (referred to as ref modifier) static void Foo(ref int p) {++p;}

Expressions and Operations An expression is a sequence of operators and operands that specifies a computation. C# has unary operators, binary operators, and one ternary operator. Complex expressions can be built because an operand may itself be an expression Example: ((1 + 2) / 3) Operator precedence

Statements Execution in a C# program is specified by a series of statements that execute sequentially in the textual order in which they appear A statement may assign an expression to a variable, repeatedly execute a list of statements, or jump to another statement Multiple statements can be grouped together, zero or more statements may be enclosed in braces to form a statement block Many different types of statements

Expression Statements An expression statement evaluates an expression, either assigning its result to a variable or generating side effects (i.e., invocation, new, ++, -- An expression statement ends in a semicolon x = 5 + 6; // assign result x++; // side effect y = Math.Min(x, 20); // side effect and assign result Math.Min(x, y); // discards result, but ok, there is a side effect x == y; // error, has no side effect, does not assign result

Declaration Statements A declaration statement declares a new variable, optionally assigning the result of an expression to that variable A declaration statement ends in a semicolon The scope of a local or constant variable extends to the end of the current block bool a = true; while(a) { int x = 5; if (x==5) { int y = 7; int x = 2; // error, x already defined } Console.WriteLine(y); // error, y is out of scope

Selection Statements Conditionally control the flow of program execution The if-else statement: An if-else statement executes code depending on whether a boolean expression is true int Compare(int a, int b) { if (a>b) return 1; else if (a<b) return -1; return 0; } Umbrella GetUmbrella (bool rainy, bool sunny, bool windy) { if ((rainy || sunny) && ! windy) return umbrella; return null; }

Selection Statements The switch statement: let you branch program execution based on a selection of possible values a variable may have The switch statements can only evaluate a predefined type or enum The end of each case statement must be unreachable The break statement The return statement void Award(int x) { switch(x) { case 1: Console.WriteLine(“1st class!"); break; case 2: Console.WriteLine(“2nd class"); default: Console.WriteLine("Don't quit"); }

Loop Statements A sequence of statements to execute repeatedly with the while, do while, for, and foreach statements The while loop: express is tested before the block is executed The do-while loop: express is tested at the end of block int i = 0; while (i<5) { Console.WriteLine (i); i++; } int i = 8; do { Console.WriteLine (i); i++; } while (i<5);

Loop Statements The for loop contains three parts A statement executed before the loop begins A boolean expression, if true, execute the block A statement executed after each iteration of the block The foreach statement: works on any collection (including arrays) for (int i=0; i<10; i++) Console.WriteLine(i); foreach (Stick stick in dynamite) Console.WriteLine(stick); for (int i=0; i<dynamite.Length; i++) Console.WriteLine(dynamite [i]);

Jump Statements Including: break, continue, return, goto, and throw The break statement: transfer execution from the loop/switch block to the next statement The continue statement: forgo the remaining statements in the loop, start the next iteration The return statement: exit the method, return an expression The goto statement: don’t use it! The throw statement: throw an exception Umbrella GetUmbrella (bool rainy, bool sunny, bool windy) { if ((rainy || sunny) && ! windy) return umbrella; return null; }

The using Statement The using statement provides an elegant syntax for declaring and then calling the Dispose method of variables that implement IDisposable using (FileStream fs = new FileStream (fileName,FileMode.Open)) { ... }

Namespaces A namespace lets you group related types into a hierarchical categorization Namespaces can be nested Using a type with fully qualified name Using the “using” keyword namespace MyCompany { namespace MyProduct { namespace Drawing { class Point {int x, y, z;} delegate void PointInvoker(Point p); } MyCompany.MyProduct.Drawing.Point x; using MyCompany.MyProduct.Drawing; class Test { static void Main() { Point x; }

Classes and Structs Classes and structs are two of the basic constructs of the common type system Each is a data structure that encapsulates a set of data and behaviors that belong together as a logical unit A class or struct can specify how accessible each of its members is to code outside of the class or struct Methods and variables that are not intended to be used from outside can be hidden to limit the potential for coding errors or malicious exploits The data and behaviors are the members of the class or struct, and they include its methods, properties, and events, and so on

Classes and Structs A class or struct declaration is a blueprint for creating instances or objects at run time If you define a class or struct called Person, Person is the name of the type. If you declare and initialize a variable p of type Person, p is said to be an object or instance of Person Person p; Multiple instances of the same Person type can be created, and each instance can have different values in its properties and fields

Classes and Structs In general, classes are used to model more complex behavior, or data that is intended to be modified after a class object is created Structs are best suited for small data structures that contain primarily data that is not intended to be modified after the struct is created

Members of a Class or Struct Fields Constants Properties Methods Constructors Destructors Indexers Delegates Operators Events

Members of a Class or Struct: Fields A field is a variable of any type that is declared directly in a class or struct A class or struct may have instance fields or static fields or both you should use fields only for variables that have private or protected accessibility public class CalendarEntry { // private field  private DateTime date; // public field (Generally not recommended)  public string day;

Members of a Class or Struct: Properties A property is a member that provides a flexible mechanism to read, write, or compute the value of a private field Properties can be used as if they are public data members, but they are actually special methods called accessors This enables data to be accessed easily and still helps promote the safety and flexibility of methods

Members of a Class or Struct: Properties class TimePeriod { private double seconds; public double Hours { get { return seconds / 3600; } set { seconds = value * 3600; } } class Program { static void Main() { // Assigning the Hours property causes the 'set' accessor to be called TimePeriod t = new TimePeriod(); // Evaluating the Hours property causes the 'get' accessor to be called t.Hours = 24; System.Console.WriteLine("Time in hours: " + t.Hours); } } Example Program#7

Members of a Class or Struct: Methods Methods define the actions that a class can perform. Methods can take parameters that provide input data, and can return output data through parameters. Methods can also return a value directly, without using a parameter class SimpleMath { public int AddTwoNumbers(int number1, int number2) { return number1 + number2; } public int SquareANumber(int number) { return number * number; }

Members of a Class or Struct: Constructor Whenever a class or struct is created, its constructor is called A class or struct may have multiple constructors that take different arguments Constructors enable the programmer to set default values, limit instantiation, and write code that is flexible and easy to read If you do not provide a constructor for your object, C# will create one by default that instantiates the object and sets member variables to the default values

Members of a Class or Struct: Constructor public class Taxi { public bool isInitialized; public Taxi() { isInitialized = true; } class TestTaxi { static void Main() { Taxi t = new Taxi(); Console.WriteLine(t.isInitialized); } Example Program#8

Members of a Class: Destructor Destructors are used to destruct instances of classes Destructors cannot be defined in structs. They are only used with classes. A class can only have one destructor. Destructors cannot be inherited or overloaded. Destructors cannot be called. They are invoked automatically. A destructor does not take modifiers or have parameters. class Car { ~Car() // destructor { // cleanup statements... }

Members of a Class: Indexers Indexers allow instances of a class or struct to be indexed just like arrays Indexers resemble properties except that their accessors take parameters class SampleCollection<T> { // Declare an array to store the data elements  private T[] arr = new T[100]; // Define the indexer  // This indexer returns or sets the corresponding element //from the internal array public T this[int i] { get { return arr[i]; } set { arr[i] = value; }

Members of a Class: Indexers // This class shows how client code uses the indexer class Program { static void Main(string[] args) { // Declare an instance of the SampleCollection type SampleCollection<string> stringCollection = new SampleCollection<string>(); // Use [] notation on the type stringCollection[0] = "Hello, World"; System.Console.WriteLine(stringCollection[0]); } } // Output:  // Hello, World. Example Program#9

Members of a Class: Delegates A delegate is a type that represents references to methods with a particular parameter list and return type When you instantiate a delegate, you can associate its instance with any method with a compatible signature and return type You can invoke the method through the delegate instance (callback method) Delegates are used to pass methods as arguments to other methods Event handlers are nothing more than methods that are invoked through delegates

Trying out Creating a new project in Visual Studio Choose Visual C# Console Application Change project name to: CsharpPractice

Trying out Here is what you see after the project was created Add your code in static void Main()

Trying out Normally, when you want to execute the program, you click the “Start Debugging” button, or F5 However, for console app, you do not have a chance to see anything before the console is closed You can use the trick described here: http://www.kobashicomputing.com/running-your-console-application-within-visual-studio

Run Console App from within Visual Studio Fisrt step: Tools/External Tools

Run Console App from within Visual Studio Click the Add button to create a new entry Enter in the new title for your console app => will appear in the Tools menu (CsharpPractice) Click the … button and select the executable to run Click the “Use Output” window and “Prompt for arguments” checkboxes

Run Console App from within Visual Studio Head over to the Tools menu and you will see your console app as a menu item