10 C# Developer & Programmer interview questions and answers

A typical C# program consists of a namespace declaration, a class, methods, attributes, a main method, statements, expressions, and comments. A potential example for printing “Hello World” to the console is detailed below.

using System;
namespace HelloWorldApplication
{
  class HelloWorld
  {
    static void Main(string[] args)
    {
      Console.WriteLine("Hello World");
      Console.ReadKey();
    }
  }
}

The three ways to pass a parameter to a method are detailed below.

• Value Parameters: Passing a parameter to a method by value creates a new storage location for the value parameter. Any changes to the value parameter by the method have no effect on the argument.
• Reference Parameters: Passing a parameter to a method by reference can be achieved by using the ref keyword. Instead of creating a new storage location for the parameter, the method accesses the memory location of the argument and passes it as a parameter. Changes made to the parameter will also affect the argument.
• Output Parameters: The out keyword allows a method to return two values from a function. It's similar to passing a reference parameter, except in this case data is being transferred out of the method.

This is an open-ended coding question that is likely to produce a variety of answers. What you’re really looking for is how the developer chooses to solve the problem. Do they settle for the obvious one-liner, return intArray.Where(i => i % 2 == 0).sum() or will they notice the high probability of overflow and instead opt for something more nuanced like the sample answer below?

static long TotalAllEvenInts(int[] intArray) {
  return (from i in intArray where i % 2 == 0 select (long)i).Sum();
}

Experienced C# developers will take this as an opportunity to show off their knowledge of C# language constructs that make simple solutions like the one above possible.

Most of the built-in operators available in C# can be overloaded or redefined using the operator keyword. The sample code below depicts the syntax used to implement the addition operator (+) for a user-defined class.

public static Rectangle operator+ (Rectangle b, Rectangle c)
{
  Rectangle rectangle = new Rectangle();
  rectangle.length = b.length + c.length;
  rectangle.breadth = b.breadth + c.breadth;
  rectangle.height = b.height + c.height;
  return rectangle;
}

The difference between dynamic and object type variables has to do with when the type checking takes place during the application lifecycle. Dynamic type variables handle type checking at run time, while object type variables handle type checking during compile time.

Encapsulation is a classic object-oriented design principle that reduces coupling between objects and encourages maintainable code. It involves enclosing objects within a logical package by limiting access to implementation details. In C#, this is accomplished through the access specifiers—public, private, protected, internal, and protected internal.

This program tests the prospective developer on their experience working with loops and delegates. At first glance, one would expect the program to output the numbers 0 to 15, fifteen times. Instead, the number 15 is printed fifteen times. Since the delegate is being added within the for loop, and because the delegate is only referencing the variable i instead of the value itself, the loop sets the value of the variable i to 15 before it is invoked within each delegate.

Nullable types are data types that, in addition to their normal values, also contain a defined data type for null. Nullable types exist to help integrate C#, which generally works with value types, and databases, which often use null values. You can declare a nullable type in C# using the following syntax:

?  = null;

Structs are used to create structures, a value type that is used to represent a record. Structs play a similar role to classes, which are a reference type in C#. Since structs are value types, they are allocated and deallocated on the stack or inline in containing types. This generally makes structs cheaper to allocate or deallocate than classes, which are reference types. Reference types are allocated on the heap and garbage-collected, which tends to take up more resources. If the instances of a type are small and short-lived, it makes sense to define a value type using structs. The opposite is true when it comes to boxing and unboxing. A value type can get boxed when it is cast to a reference type or some other interface it implements. Because boxes are objects allocated to the heap and deallocated via garbage collection, too much boxing and unboxing of a value can negatively impact performance. Reference types like classes are preferred in these situations.

Generics allow a developer to define a class or method that can work with virtually any data type by delaying specification of the programming elements' data types until they are needed. Generics come with a number of features.

• They make C# code reusable, type safe, and performance optimized.
• They allow the developer to create generic classes, methods, events, delegates, and interfaces.
• They allow the developer to create generic collection classes in the System.Collections.Generic namespace.
• They make it possible to get real-time information on the types used in a generic data type at runtime via reflection.