Interview Questions and Answers
Intermediate / 1 to 5 years experienced level questions & answers
Ques 1. What is protected accessibility?
Access is restricted to types derived from the containing class.
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Ques 2. What is protected internal accessibility?
Access is restricted to types derived from the containing class or from files within the same assembly.
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Ques 3. What is the default accessibility for a class?
internal for a top level class, private for a nested one.
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Ques 4. What is the default accessibility for members of an interface?
public
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Ques 5. Methods must declare a return type, what is the keyword used when nothing is returned from the method?
Void
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Ques 6. What is a reference parameter?
Reference parameters reference the original object whereas value parameters make a
local copy and do not affect the original. Some example code is shown:
using System;
namespace Console1
{
class Class1
{
static void Main(string[] args)
{
TestRef tr1 = new TestRef();
TestRef tr2 = new TestRef();
tr1.TestValue = "Original value";
tr2.TestValue = "Original value";
int tv1 = 1;
int tv2 = 1;
TestRefVal(ref tv1, tv2, ref tr1, tr2);
Console.WriteLine(tv1);
Console.WriteLine(tv2);
Console.WriteLine(tr1.TestValue);
Console.WriteLine(tr2.TestValue);
Console.ReadLine();
}
static public void TestRefVal(ref int tv1Parm,
int tv2Parm,
ref TestRef tr1Parm,
TestRef tr2Parm)
{
tv1Parm = 2;
tv2Parm = 2;
tr1Parm.TestValue = "New value";
tr2Parm.TestValue = "New value";
}
}
}
class TestRef
{
public string TestValue;
}
The output for this is:
2
1
New value
New value
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Ques 7. What is an overloaded method?
An overloaded method has multiple signatures that are different.
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Ques 8. If I have a constructor with a parameter, do I need to explicitly create a default constructor?
Yes
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Ques 9. What is a delegate?
A delegate in C# is like a function pointer in C or C++. A delegate is a variable that calls
a method indirectly, without knowing its name. Delegates can point to static or/and
member functions. It is also possible to use a multicast delegate to point to multiple
functions.
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Ques 10. Write some code to use a delegate.
Member function with a parameter
using System;
namespace Console1
{
class Class1
{
delegate void myDelegate(int parameter1);
static void Main(string[] args)
{
MyClass myInstance = new MyClass();
myDelegate d = new myDelegate(myInstance.AMethod);
d(1); // <--- Calling function without knowing its name.
Test2(d);
Console.ReadLine();
}
static void Test2(myDelegate d)
{
d(2); // <--- Calling function without knowing its name.
}
}
class MyClass
{
public void AMethod(int param1)
{
Console.WriteLine(param1);
}
}
}
Multicast delegate calling static and member functions
using System;
namespace Console1
{
class Class1
{
delegate void myDelegate(int parameter1);
static void AStaticMethod(int param1)
{
Console.WriteLine(param1);
}
static void Main(string[] args)
{
MyClass myInstance = new MyClass();
myDelegate d = null;
d += new myDelegate(myInstance.AMethod);
d += new myDelegate(AStaticMethod);
d(1); //both functions will be run.
Console.ReadLine();
}
}
class MyClass
{
public void AMethod(int param1)
{
Console.WriteLine(param1);
}
}
}
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Ques 11. What is a value type and a reference type?
A reference type is known by a reference to a memory location on the heap.
A value type is directly stored in a memory location on the stack. A reference type is
essentially a pointer, dereferencing the pointer takes more time than directly accessing
the direct memory location of a value type.
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Ques 12. string is an alias for what?
System.String
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Ques 13. How do you dereference an object?
Set it equal to null.
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Ques 14. In terms of references, how do == and != (not overridden) work?
They check to see if the references both point to the same object.
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Ques 15. What is the default value for a bool?
False
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Ques 16. Write code for an enumeration.
public enum animals {Dog=1,Cat,Bear};
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Ques 17. Can a struct have methods?
Yes
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Ques 18. What is checked { } and unchecked { }?
By default C# does not check for overflow (unless using constants), we can use
checked to raise an exception. E.g.:
static short x = 32767; // Max short value
static short y = 32767;
// Using a checked expression
public static int myMethodCh()
{
int z = 0;
try
{
z = checked((short)(x + y));
//z = (short)(x + y);
}
catch (System.OverflowException e)
{
System.Console.WriteLine(e.ToString());
}
return z; // Throws the exception OverflowException
}
This code will raise an exception, if we remove unchecked as in:
//z = checked((short)(x + y));
z = (short)(x + y);
Then the cast will raise no overflow exception and z will be assigned 2. unchecked can
be used in the opposite way, to say avoid compile time errors with constanst overflow.
E.g. the following will cause a compiler error:
const short x = 32767; // Max short value
const short y = 32767;
public static int myMethodUnch()
{
int z = (short)(x + y);
return z; // Returns -2
}
The following will not:
const short x = 32767; // Max short value
const short y = 32767;
public static int myMethodUnch()
{
int z = unchecked((short)(x + y));
return z; // Returns -2
}
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Ques 19. Can assignment operators be overloaded directly?
No
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Ques 20. What do operators is and as do?
as acts is like a cast but returns a null on conversion failure. Is comares an object to a
type and returns a boolean.
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Ques 21. What is the difference between the new operator and modifier?
The new operator creates an instance of a class whereas the new modifier is used to
declare a method with the same name as a method in one of the parent classes.
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Ques 22. Explain sizeof and typeof.
typeof obtains the System.Type object for a type and sizeof obtains the size of a type.
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Ques 23. Contrast ++count vs. count++.
Some operators have temporal properties depending on their placement. E.g.
double x;
x = 2;
Console.Write(++x);
x = 2;
Console.Write(x++);
Console.Write(x);
Returns
323
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