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Friday, 18 September 2015

Common C#.Net Interview Questions and Answers pdf

101. What does assert() do? 
In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.

102. How do I get deterministic finalization in C#? 
In a garbage collected environment, it's impossible to get true determinism. However, a design pattern that we recommend is implementing IDisposable on any class that contains a critical resource. Whenever this class is consumed, it may be placed in a using statement, as shown in the following example:
using(FileStream myFile = File.Open(@"c:temptest.txt",
FileMode.Open))
{
int fileOffset = 0;
while(fileOffset < myFile.Length)
{
Console.Write((char)myFile.ReadByte());
fileOffset++;
}
}
When myFile leaves the lexical scope of the using, its dispose method will be called.

103. How can I get around scope problems in a try/catch? 
If you try to instantiate the class inside the try, it'll be out of scope when you try to access it from the catch block. A way to get around this is to do the following: Connection conn = null;
try
{
conn = new Connection();
conn.Open();
}
finally
{
if (conn != null) conn.Close();
}
By setting it to null before the try block, you avoid getting the CS0165 error (Use of possibly unassigned local variable 'conn').

104. Why do I get an error (CS1006) when trying to declare a method without specifying a return type? 
If you leave off the return type on a method declaration, the compiler thinks you are trying to declare a constructor. So if you are trying to declare a method that returns nothing, use void. The following is an example: // This results in a CS1006 error public static staticMethod (mainStatic obj) // This will work as wanted public static void staticMethod (mainStatic obj)

105. How do I convert a string to an int in C#?
Here's an example: using System;
class StringToInt
{
public static void Main()
{
String s = "105";
int x = Convert.ToInt32(s);
Console.WriteLine(x);
}
}

106. How do you directly call a native function exported from a DLL? 
Here's a quick example of the DllImport attribute in action: using System.Runtime.InteropServices;
class C
{
[DllImport("user32.dll")]
public static extern int MessageBoxA(int h, string m, string c, int type);
public static int Main()
{
return MessageBoxA(0, "Hello World!", "Caption", 0);
}
}
This example shows the minimum requirements for declaring a C# method that is implemented in a native DLL. The method C.MessageBoxA() is declared with the static and external modifiers, and has the DllImport attribute, which tells the compiler that the implementation comes from the user32.dll, using the default name of MessageBoxA. For more information, look at the Platform Invoke tutorial in the documentation.

107. What is the .NET datatype that allows the retrieval of data by a unique key? 
HashTable.

108. How do you specify a custom attribute for the entire assembly (rather than for a class)? 
Global attributes must appear after any top-level using clauses and before the first type or namespace declarations. An example of this is as follows:
using System;
[assembly : MyAttributeClass]
class X {}
Note that in an IDE-created project, by convention, these attributes are placed in
AssemblyInfo.cs.

109. What is the difference between a struct and a class in C#? 
From language spec:
The list of similarities between classes and structs is as follows. Longstructs can implement interfaces and can have the same kinds of members as classes. Structs differ from classes in several important ways; however, structs are value types rather than reference types, and inheritance is not supported for structs. Struct values are stored on the stack or in-line. Careful programmers can sometimes enhance performance through judicious use of structs. For example, the use of a struct rather than a class for a Point can make a large difference in the number of memory allocations performed at runtime. The program below creates and initializes an array of 100 points. With Point implemented as a class, 101 separate objects are instantiated-one for the array and one each for the 100 elements.

110. What is the difference between the Debug class and Trace class? 
Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.


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