C# Essentials

1. C# Essentials, 2nd Edition
   
2. By: Ben Albahari; Peter Drayton; Brad Merrill
   
3. Publisher: O'Reilly Media, Inc.
   
4. Pub. Date: January 25, 2002
   
5. Print ISBN-13: 978-0-596-00315-9
   
6. Pages in Print Edition: 218
   
7. Subscriber Rating: 0 out of 5 rating [0 Ratings]

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1. Example: Building and Using Types
   
2. In this program, we build our own type called Counter and another type called Test that uses instances of the Counter. The Counter type uses the predefined type int, and the Test type uses the static function member WriteLine of the Console class defined in the System namespace:
   
3. // Imports types from System namespace, such as Console
   
4. using System;
   
5. class Counter { // New types are typically classes or structs
   
6.   // --- Data members ---
   
7.   int value; // field of type int
   
8.   int scaleFactor; // field of type int
   
9. 
   
10.   // Constructor, used to initialize a type instance
    
11.   public Counter(int scaleFactor) {
    
12.     this.scaleFactor = scaleFactor;  
    
13.   }
    
14.   // Method
    
15.   public void Inc(  ) {
    
16.     value+=scaleFactor;
    
17.   }
    
18.   // Property
    
19.   public int Count {
    
20.     get {return value; }
    
21.   }
    
22. }
    
23. class Test {
    
24.   // Execution begins here
    
25.   static void Main(  ) {
    
26. 
    
27.     // Create an instance of counter type
    
28.     Counter c = new Counter(5);
    
29.     c.Inc(  );
    
30.     c.Inc(  );
    
31.     Console.WriteLine(c.Count); // prints "10";
    
32. 
    
33.     // Create another instance of counter type
    
34.     Counter d = new Counter(7);
    
35.     d.Inc(  );
    
36.     Console.WriteLine(d.Count); // prints "7";
    
37.    }
    
38. }

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1. Definite Assignment
   
2. Variables in C# (except in unsafe contexts) 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. For example:
   
3. using System;
   
4. class Test {
   
5.   int v;
   
6.   // Constructors that initialize an instance of a Test
   
7.   public Test(  ) {} // v will be automatically assigned to 0
   
8.   public Test(int a) { // explicitly assign v a value
   
9.      v = a;
   
10.   }
    
11.   static void Main(  ) {
    
12.     Test[] iarr = new Test [2]; // declare array
    
13.     Console.WriteLine(iarr[1]); // ok, elements assigned to null
    
14.     Test t;
    
15.     Console.WriteLine(t); // error, t not assigned
    
16.   }
    
17. }

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