C# Programming - MCQ Practice Questions

Both int? and Nullable<int> represent the same nullable integer type. int? is the shorthand syntax for Nullable<int>. They allow the variable to hold a null value in addition to integer values.

'params' allows a method to accept a variable number of arguments of the same type as an array. For example: void Method(params int[] numbers) can accept 0 or more integers.

In C#, the == operator for strings compares their values, not references. Since both s1 and s2 contain "Hello", the result is true. This is different from object references comparison.

List<T> maintains insertion order and allows duplicates. HashSet<T> doesn't allow duplicates. Dictionary<K,V> maintains key-value pairs. SortedSet<T> keeps elements sorted without duplicates.

'abstract' keyword creates a class that serves as a blueprint for derived classes and cannot be instantiated directly. Abstract classes can contain abstract methods that must be implemented by derived classes.

LINQ (Language Integrated Query) provides a unified syntax for querying different data sources like collections, databases, XML, etc. It allows developers to write queries in C# syntax.

The 'finally' block executes regardless of whether an exception is thrown or caught. It is used for cleanup operations like closing file streams or database connections.

Post-increment (x++) returns the current value first, then increments. So y gets 10, then x becomes 11.

const creates a compile-time constant. readonly allows assignment only in constructor or at declaration. static makes it class-level, and fixed is for pointers.

var is implicitly typed. The type is inferred and set at compile-time based on the right-hand side assignment, providing type safety.

char 'A' has ASCII value 65. Casting to int gives the numeric ASCII value.

Method overloading requires different parameter types, count, or order. Return type alone is not enough. C# fully supports overloading.

Option B is correct as both branches return int (1 or 0). Option A has type mismatch (string in int). Option C has wrong syntax. Option D has type mismatch.

ref parameters must be initialized before being passed to a method, while out parameters don't require initialization beforehand. The method must assign a value to out parameters before returning.

The null-coalescing operator (?.) with null-coalescing assignment (??) ensures that when str is null, the expression evaluates to null, and then ?? provides the default value 'DEFAULT'.

The 'is' operator checks reference equality by default and is used for type checking, while '==' can be overloaded by classes to provide custom equality logic.