400+ C# Interview Questions Practice Test

What is the primary interface in C#? The primary interface in C# is System.Runtime.Interfaces. This interface is part of the .NET Common Language Runtime (CLR) and defines methods for a range of core data types, including arrays, collections like dictionaries, lists, queues, stacks, and so on. It's important to note that System.Runtime.Interfaces doesn't contain all interfaces; it's just one of several assemblies that are part of the .NET framework. Other assemblies include those for generics (System.Collections.Generic), for example.

What is the 'using' statement in C#? The 'using' statement is used to include types defined within another assembly, and at the same time to define variables of those included types. It provides a convenient syntax for creating instances of classes that implement disposable pattern, which means that when the 'using' block is exited (normally by reaching the end of the file), all the resources that were obtained via the System.IDisposable` interface within that block are disposed of automatically.

What are generics in C#? Generics in C# refer to the feature that allows classes, interfaces, and value types (class, interface, or struct) to be defined with parameters that can be of any type specified when defining the class, interface, or struct. The purpose of generics is code reuse for different data types without having to write new code for each type. A generic class is declared within angle brackets right after the class keyword. For example:

public class <T>>
{
    // Class implementation goes here.
}

Here, <T>> is a placeholder for the actual data type that you want to define the generic class for. The actual type is specified when declaring a concrete class that inherits from this generic class.

What are events in C#? Events in C# refer to the EventHandler pattern, which is a way of handling events in a loosely coupled fashion. An event is an instance-level signal that can be raised by an object (raiser) when certain conditions are encountered. The event is then potentially handled by one or more event handlers (handlers). This pattern enables objects to communicate with each other without being tightly coupled, thus facilitating a form of asynchronous communication between components.

What is the role of the 'default' constructor in C#? In C#, when you instantiate a new object from a class that has a publicly accessible constructor, the 'default constructor is automatically called if no explicit constructor call is made. The 'default constructor acts as an overloaded constructor and does not take any parameters. It is used to initialize resources for a newly created object when no other constructors are explicitly called for that class.

What is the purpose of 'ref’ keyword in C#? The ref keyword in C# is used to specify a reference type. When you use ref, you're declaring that the variable will hold a reference to an object which is already allocated and ready for use by another class or module. This means that the garbage collector will not automatically free up memory for this object when it goes out of scope because ownership of the object is transferred to the new variable that holds the ref keyword.

What are 'partial methods' in C#? Partial methods in C# (also known as partial matching or pattern matching methods) are methods used within a switch statement block for checking conditions against a set of cases and executing code blocks corresponding to matching case(s). When implementing a switch statement, you can define two sets of method bodies. One set is defined before the switch block itself, and another set is defined after the switch block but still within the overall switch statement. The C# compiler will automatically merge these two sets of methods together during compilation.

What are 'attributes' in C#? Attributes in C# provide a mechanism for associating metadata with entities such as classes, methods, properties, indexers, and even individual variables at the language level. They can be used to store additional information about these entities that is not part of the entity's state or behavior. Attributes are applied using the square brackets [] syntax before the entity's name, for example:

[AttributeUsage(AttributeTargets.Class)]
public class MyClass
{
    // Class implementation goes here.
}

What is the 'checked' keyword in C#?

The 'checked' keyword in C# is used within the switch statement block to indicate that the case label being evaluated against the switch expression is mutually exclusive with other cases. That is, if one case evaluates to true, then all other cases are guaranteed to evaluate to false. This ensures that only one of the cases will be true at any given time.

What are 'unsafe' pointers in C#? Unsafe pointers in C# are pointers that can be used to hold references to memory locations that are outside of the managed heap of the .NET runtime. They enable the programmer to directly interact with and manipulate unmanaged native memory resources. These pointers are declared using the unsafe contextual keyword along with the fixed (or fixed partial) modifiers within a using statement block, for example:

public class UnsafeExample
{
    fixed (void*)ptr = value;
    
    // ... other managed code ...
    
    unsafe
    {
        byte* ptr = &value;
        // ... manipulate 'unsafe' pointer here ...
    }
}

Here, &value represents the address of a variable value, and ptr is the pointer that holds the memory address of value. The fixed (or fixed partial) modifier prevents the garbage collector from moving the memory location that ptr points to during the runtime's garbage collection process. Remember, the specific terminology and usage can vary slightly based on the version of C# you are using (e.g., C# 7.2 vs. C# 8.0 and later), and some terms may have been introduced or clarified in more recent versions of the language. It's also important to note that while I strive for accuracy, the explanations provided here are intended for educational and informational purposes, and they may not cover every single aspect or usage scenario in exhaustive detail.