Takeaway: Software development hiring managers and potential interviewees will find these open-ended C# proficiency interview questions and answers useful.
Good help is hard to find. There is an art to finding a developer who fits well in your organization in terms of personality and work ethic; fortunately, it’s more straightforward to determine their technical expertise.
I worked at a couple of places where development managers loved drilling job candidates on syntax while having them write code, and it was clearly a stressful experience for the interviewee. I do not like asking specific syntax questions during interviews since most developers do not know language syntax or class names off the top of their heads.
In terms of the basic interview, I prefer to ask open-ended questions where the candidate can explain concepts and how they would attack problems. Some organizations like to give candidates tests or have them eyeball code snippets to spot problems, and I think those are good evaluation tools.
This is the first installment in our series of programming language-specific development interview questions and answers. Here is a list of questions (and the answers to those questions) that will help you get a feel for a candidate’s proficiency with C#. You can ask follow-up questions based on their replies.
Note: This content is also available as a downloadable
PDF.
What are namespaces, and how they are used?
Namespaces are used to organize classes within the .NET Framework. They dictate the logical structure of the code. They are analogous to Java packages, with the key difference being Java packages define the physical layout of source files (directory structure) while .NET namespaces do not. However, many developers follow this approach and organize their C# source files in directories that correlate with namespaces. The .NET Framework has namespaces defined for its many classes, such as System.Xml–these are utilized via the using statement. Namespaces are assigned to classes via the namespace keyword.
What is a constructor?
A constructor is a class member executed when an instance of the class is created. The constructor has the same name as the class, and it can be overloaded via different signatures. Constructors are used for initialization chores.
What is the GAC, and where is it located?
The GAC is the Global Assembly Cache. Shared assemblies reside in the GAC; this allows applications to share assemblies instead of having the assembly distributed with each application. Versioning allows multiple assembly versions to exist in the GAC–applications can specify version numbers in the config file. The gacutil command line tool is used to manage the GAC.
Why are strings in C# immutable?
Immutable means string values cannot be changed once they have been created. Any modification to a string value results in a completely new string instance, thus an inefficient use of memory and extraneous garbage collection. The mutable System.Text.StringBuilder class should be used when string values will change.
What is DLL Hell, and how does .NET solve it?
DLL Hell describes the difficulty in managing DLLs on a system; this includes multiple copies of a DLL, different versions, and so forth. When a DLL (or assembly) is loaded in .NET, it is loaded by name, version, and certificate. The assembly contains all of this information via its metadata. The GAC provides the solution, as you can have multiple versions of a DLL side-by-side.
How are methods overloaded?
Methods are overloaded via different signatures (number of parameters and types). Thus, you can overload a method by having different data types, different number of parameters, or a different order of parameters.
How do you prevent a class from being inherited?
The sealed keyword prohibits a class from being inherited.
What is the execution entry point for a C# console application?
The Main method.
How do you initiate a string without escaping each backslash?
You put an @ sign in front of the double-quoted string.
String ex = @"This has a carriage return\r\n"
What is the difference between a struct and a class?
Structs cannot be inherited. Structs are passed by value and not by reference. Structs are stored on the stack not the heap. The result is better performance with Structs
What is a singleton?
A singleton is a design pattern used when only one instance of an object is created and shared; that is, it only allows one instance of itself to be created. Any attempt to create another instance simply returns a reference to the first one. Singleton classes are created by defining all class constructors as private. In addition, a private static member is created as the same type of the class, along with a public static member that returns an instance of the class. Here is a basic example:
public
class SingletonExample {
private static SingletonExample _Instance;
private SingletonExample () { }
public static SingletonExample GetInstance() {
if (_Instance == null) {
_Instance = new SingletonExample ();
}
return _Instance;
}
}
What is boxing?
Boxing is the process of explicitly converting a value type into a corresponding reference type. Basically, this involves creating a new object on the heap and placing the value there. Reversing the process is just as easy with unboxing, which converts the value in an object reference on the heap into a corresponding value type on the stack. The unboxing process begins by verifying that the recipient value type is equivalent to the boxed type. If the operation is permitted, the value is copied to the stack. (1)
Some more Questions and Answer:
C# .NET
interview questions
Good
for preparation and general self-testing, but too specific for the actual job
interview. This was sent in by a job applicant getting ready to step into the
.NET field in India.
Are private class-level
variables inherited? - Yes, but they are not accessible,
so looking at it you can honestly say that they are not inherited. But they
are.
Why does Dll Import not work
for me? - All methods marked with the
DllImport attribute must be marked as public static extern.
Why does my Windows application
pop up a console window every time I run it? - Make sure that the target type
set in the project properties setting is set to Windows Application, and not
Console Application. If you’re using the command line, compile with
/target:winexe, not /target:exe.
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)
Why do I get a syntax error
when trying to declare a variable called checked?- The word checked is a keyword in
C#.
Why do I get a security
exception when I try to run my C# app? - Some security exceptions are
thrown if you are working on a network share. There are some parts of the
frameworks that will not run if being run off a share (roaming profile, mapped
drives, etc.). To see if this is what’s happening, just move the executable
over to your local drive and see if it runs without the exceptions. One of the
common exceptions thrown under these conditions is
System.Security.SecurityException. To get around this, you can change your
security policy for the intranet zone, code group 1.2, (the zone that running
off shared folders falls into) by using the caspol.exe tool.
Why do I get a CS5001: does not have an entry
point defined error when compiling? - The most common problem is that
you used a lowercase ‘m’ when defining the Main method. The correct way to
implement the entry point is as follows: class test
{
static void Main(string[]
args)
{
}
What optimizations does the C#
compiler perform when you use the /optimize+ compiler option? - The following is a response from
a developer on the C# compiler team: We get rid of unused locals (i.e., locals
that are never read, even if assigned). We get rid of unreachable code. We get
rid of try-catch with an empty try. We get rid of try-finally with an empty
try. We get rid of try-finally with an empty finally. We optimize branches over
branches: gotoif A, lab1 goto lab2: lab1: turns into: gotoif !A, lab2 lab1: We
optimize branches to ret, branches to next instruction, and branches to
branches.
What is the syntax for calling
an overloaded constructor within a constructor (this() and constructorname()
does not compile)?
The syntax for calling another
constructor is as follows:
class B { B(int i) { } } class C : B { C() : base(5)
// call base constructor B(5) { } C(int i) : this() // call C() { } public
static void Main() {} }
What is the equivalent to
regsvr32 and regsvr32 /u a file in .NET development?
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.
Is there regular expression
(regex) support available to C# developers? - Yes. The .NET class libraries provide support for regular
expressions. Look at theSystem.Text.RegularExpressions
namespace.
Is there any sample C# code for
simple threading? - Yes:
using System;
using System.Threading;
class ThreadTest
{
public void runme()
{
Console.WriteLine("Runme Called");
}
public static void Main(String[] args)
{
ThreadTest b = new ThreadTest();
Thread t = new Thread(new ThreadStart(b.runme));
t.Start();
}
}
Is there an equivalent of
exit() for quitting a C# .NET application?
Yes, you can use System.Environment.Exit(int exitCode) to exit the
application or Application.Exit() if it’s a Windows Forms app.
Is there a way to force garbage
collection? - Yes. Set all references to null and then call
System.GC.Collect(). If you need to have some objects destructed, and
System.GC.Collect() doesn’t seem to be doing it for you, you can force finalizers
to be run by setting all the references to the object to null and then calling
System.GC.RunFinalizers().
Is
there a way of specifying which block or loop to break out of when working with
nested loops? - The easiest way is to use goto:
. using System;
class BreakExample
{
public static void Main(String[] args) {
for(int i=0; i<3 i="i" o:p="o:p">
{
Console.WriteLine("Pass {0}: ", i);
for( int j=0 ; j<100 j="j" o:p="o:p">
{
if ( j == 10)
goto done;
Console.WriteLine("{0} ", j);
}
Console.WriteLine("This will not
print");
}
done:
Console.WriteLine("Loops complete.");
}
}
My switch statement works
differently than in C++! Why? - C# does not support an explicit
fall through for case blocks. The following code is not legal and will not
compile in C#:
switch(x)
{
case 0: // do something
case 1: // do something as continuation of
case 0
default: // do something in common with
//0, 1 and everything else
break;
}
To achieve the same effect in C#,
the code must be modified as shown below (notice how the control flows are
explicit):
class
Test
{
public static void Main() {
int x = 3;
switch(x)
{
case 0: // do
something
goto case 1;
case 1: // do
something in common with 0
goto default;
default: // do
something in common with 0, 1, and anything else
break;
}
}
}
Is it possible to restrict the scope of a field/method of a class to the classes in the same namespace? - There is no way to restrict to a namespace. Namespaces are never units of protection. But if you’re using assemblies, you can use the ‘internal’ access modifier to restrict access to only within the assembly.
