Which statement about partial classes in C# is true?
Correct answer C. All parts must use the partial keyword and be in the same assembly and namespace
Topic / 95 questions
C# MCQs
C# MCQs test the C Sharp language and the .NET platform it runs on, a common subject in software developer recruitment tests, computer science degrees and IT officer exams. Questions cover the CLR and garbage collection, types and conversions, operators, object-oriented programming, exceptions, delegates, generics, collections, LINQ and asynchronous code. Each answer includes a teaching explanation, and code-output questions use short single-line snippets.
What happens when Dictionary.Add is called with a key that is already present?
Correct answer B. An ArgumentException is thrown
What is printed by: int arr = new int; Console.WriteLine(arr);?
Correct answer B. 0
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What does the yield return statement do in a C# method?
Correct answer C. It returns one element of an iterator and resumes from that point on the next request
When does the body of a C# iterator method that uses yield return start running?
Correct answer D. When the caller first calls MoveNext, usually through foreach
What does this print: var list = new List { 1, 2, 3 }; var q = list.Where(x => x > 1); list.Add(4); Console.WriteLine(q.Count());?
Correct answer B. 3
What is the difference between First() and FirstOrDefault() in LINQ when the sequence is empty?
Correct answer D. First() throws InvalidOperationException; FirstOrDefault() returns the type's default value
Which LINQ query-syntax expression selects numbers greater than 5 from an array nums?
Correct answer A. from n in nums where n > 5 select n
Which LINQ method forces immediate execution of a query?
Correct answer D. ToList
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If an async method is declared as async Task GetCountAsync(), what type does await GetCountAsync() produce?
Correct answer A. int
Why should async void methods generally be avoided except for event handlers?
Correct answer B. Callers cannot await them or catch their exceptions
Which method creates a task that completes when all of several tasks have completed?
Correct answer B. Task.WhenAll
What is the purpose of attributes such as in C#?
Correct answer D. To attach declarative metadata to code elements that tools or reflection can read
A custom attribute class is named ValidatedAttribute. How can it be applied to a method in C#?
Correct answer B. [Validated] or [ValidatedAttribute]
What does a file-scoped namespace declaration such as namespace MyApp.Models; do in C# 10 and later?
Correct answer C. It places every type in the file into that namespace without an extra pair of braces
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What does the await operator do in a C# async method?
Correct answer C. It suspends the method until the awaited task completes, without blocking the thread
Inside a catch block, what is the difference between throw; and throw ex;?
Correct answer B. throw; keeps the original stack trace, while throw ex; resets it to the current point
When does a finally block execute in C#?
Correct answer B. After the try block and any catch, whether or not an exception occurred, even after return
Which keyword is used to declare an indexer in a C# class?
Correct answer A. this
What does an init accessor, as in public string Name { get; init; }, allow in C#?
Correct answer D. The property can be set only during object initialisation, then becomes read-only
About C# MCQs
The first part covers the .NET platform: the Common Language Runtime, CIL and JIT compilation, assemblies, the Base Class Library, managed code and how the garbage collector uses generations and the large object heap.
Language basics follow: value types versus reference types, sizes of built-in types, nullable value types, implicit and explicit conversions, boxing and unboxing, string immutability, var, dynamic, const and readonly, and operators such as integer division, remainder, null-conditional and null-coalescing operators, checked arithmetic and pattern matching.
Object-oriented questions deal with classes, structs and records, constructors and static constructors, inheritance with virtual, override and new, abstract and sealed classes, interfaces with default members, access modifiers, properties, init accessors and indexers.
The last part covers exceptions and the using statement, delegates, Func, Action and Predicate, events and lambdas, generics and constraints, collections, iterators with yield return, LINQ deferred execution, async and await, attributes, namespaces and partial classes.
Key facts to remember
- C# source code compiles to Common Intermediate Language (CIL), which the JIT compiler turns into native code at run time.
- string is a reference type, but strings are immutable: methods such as ToUpper return a new string.
- Integer division in C# truncates towards zero, so 7 / 2 is 3 and -7 % 3 is -1.
- Math.Round uses banker's rounding by default, so Math.Round(2.5) returns 2.
- LINQ queries such as Where use deferred execution; ToList or Count runs them immediately.
Exams that include C# MCQs
Pakistan
- NTS and PTS software developer tests
- PPSC and FPSC Computer Science Lecturer
- FPSC IT and programmer posts
- University exams
India
- Campus placements and company aptitude tests
- UGC NET Computer Science
- IBPS IT Officer
- GATE CS (programming concepts)
Bangladesh
- BCS (technical cadre)
- Bank IT officer and programmer tests
- Government assistant programmer posts
How to prepare for C# MCQs
- Learn which built-in types are value types and which are reference types; many output questions depend on copy versus reference behaviour.
- Trace code-output questions step by step, writing down each variable after every statement, especially with x++ and ++x.
- Remember the difference between override (runtime dispatch) and new (hiding based on the declared type).
- For LINQ questions, ask whether the query has actually run yet: deferred queries see later changes to the source collection.
Frequently asked questions
What is the difference between C# and .NET?
C# is a programming language. .NET is the platform that runs it, made up of the Common Language Runtime, which manages memory and execution, and the class libraries that programs use. Other languages such as F# and Visual Basic also run on .NET.
Which C# topics are asked most often in job tests?
Value and reference types, boxing, string immutability, operators and output questions, OOP with virtual, override, abstract and interfaces, access modifiers, exceptions with finally, delegates and events, collections, LINQ and async/await come up most often.
Last reviewed October 2026