C# Types Let me know if you have not received CMS emails First - PDF document

1/25/2008 Administration  CMS student list populated C# Types  Let me know if you have not received CMS emails  First assignment released Mingsheng Hong  Due on Feb. 1 CS 215, Spring 2008  Write a C# program that  takes as input regular English text  returns the transpose  Use C# style  much of what we discussed so far will be useful  should be short Review .NET Based Frameworks  Visual C# 2008 Express walkthrough  ASP.NET: web application framework  Use .NET languages in server-side web pages  .NET framework, CLR, CTS, CLS  Now supports AJAX!  ADO.NET: Use the CLR to access databases  in the manner of ODBC  provides classes for access  Microsoft XNA: game design framework  GDIAC at http://gdiac.cis.cornell.edu  CIS 300: Introduction to Computer Game Design Roadmap for Today’s Lecture Common Type System  C# types  Reference types  Value types  Boxing and unboxing  Basic C# features  Arrays  OO features  Function parameters  Iterators From MSDN 1

1/25/2008 Common Value Types Common Reference Type  string type: string  Integer types:  signed: sbyte, int, short, long  can index like char array  unsigned: byte, uint, ushort, ulong  has methods such as Split  Floating point: float, double, decimal  e.g.,  Everything in C# inherits from object  string s = “Hello”; char third = s[2];  regular objects are heavy-weight string[] split = s.Split(third);  for efficiency, need primitive types Common Types Reference Types  What is the difference between string and double?  Single inheritance in class hierarchy, rooted  reference types vs. value types in object  two families of types in C#  Simple to Java classes  Implement arbitrarily many interfaces  Similar to Java interfaces  C# classes can be abstract  must be explicitly marked as abstract (contrast with C++)  May contain non-method non-data members Reference Types: Value Types: Memory Layout Memory Layout  Refer to a memory location  Contain the actual value, not the location  very much like pointers in other languages like  Inherit from System.ValueType C/C++  treated specially by the runtime: no subclassing  Can be set to null  Copies of value types make a real copy memory memory a { 137 a { A a = new A(); } int a = 137; var of class A A b = a; int b = a; 137 b } } b 2

1/25/2008 Boxing and Unboxing Differences between Types  Copy semantics for assignment:  Value types not objects  MyClass a = new MyClass();  performance gain in common case MyClass b = a;  but can become objects on demand b.X = 10; Console.WriteLine(a.X); //output ?  called “boxing”. Reverse is “ unboxing ”  int a = 1;  Note: boxing still copies int b = a; b = 10; { memory Console.WriteLine(a); //output ? int a = 137; 137 a o1 object o1 = a;  Important for parameter passing, too int 137 object o2 = o1; 137 b int b = (int)o2; o2 } Common Value Types Enum Example  Simple types (i.e., integer and floating point)  Definition enum Color  Enum types {  has a corresponding underlying type (default: int) Red, Green, Blue }  Instantiation Color c = Color.Red; Common Value Types Struct Example  Simple types (i.e., integer and floating point)  Definition struct Point {  Enum types public int x, y;  has a corresponding underlying type (default: int) public Point(int x, int y) { this.x = x;  Struct types this.y = y;  user-defined value types }  can contain arbitrary data }  Instantiation  non-extensible (sealed subclasses) Point a = new Point(10, 10);  examples: Point, KeyValuePair a.x = 20; 3

1/25/2008 C# Variables Basic C# Features  Definite assignment • Arrays  int i; //i is a local variable • OO features  Console.WriteLine(i); //error CS0165: Use • Accessibility of unassigned local variable 'i' Class members •  Default values • Property  only for instance variables, static variables, and array elts • Indexer  eg. • Operator  string s; // s == null  double x; // x == 0.0 • Function parameters • Iterators C# Arrays C# Arrays  Can have standard C arrays  Multidimensional  int[] array = new int[30];  stored sequentially  int[][] array = new int[2][];  int[,] array = new int[10,30]; array[0] = new int[100]; array[3,7] = 137; array[1] = new int[1];  Called “jagged” arrays  Stored in random parts of the heap  Can have arbitrary dimensions  Recall that an array is an object 4