.NET Full Stack Interview Questions for Freshers: C#, ASP.NET Core, SQL & Web API
Freshers preparing for .NET Full Stack interviews should revise C#, OOP, ASP.NET Core, MVC, Entity Framework Core, Web API, SQL Server, HTML, CSS, JavaScript, Git and practical troubleshooting scenarios. Interviewers usually want to know whether you can explain basics clearly and connect them to real projects.
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C# Interview Questions
1. What is C#?
C# is an object-oriented programming language used with the .NET platform to build web, desktop, API and enterprise applications.
2. What are variables and data types?
A variable stores data. Data types such as int, string, bool, decimal and DateTime define what kind of value can be stored.
3. What is the difference between value type and reference type?
Value types store actual values, while reference types store references to objects in memory.
4. What are classes and objects?
A class is a blueprint. An object is an instance of that class created during program execution.
5. What is encapsulation?
Encapsulation hides internal data and exposes controlled access through methods or properties.
6. What is inheritance?
Inheritance allows one class to reuse or extend behavior from another class.
7. What is polymorphism?
Polymorphism allows the same method name or interface to behave differently depending on context.
8. What is abstraction?
Abstraction shows essential behavior while hiding implementation details.
9. Interface vs abstract class?
An interface defines a contract. An abstract class can include shared implementation and abstract members.
10. What is a constructor?
A constructor initializes an object when it is created.
11. What is exception handling?
Exception handling uses try, catch and finally blocks to handle runtime errors gracefully.
12. What are collections?
Collections store groups of objects. Examples include List, Dictionary, Queue and Stack.
13. What are generics?
Generics allow classes and methods to work with different data types while maintaining type safety.
14. What are delegates?
A delegate is a type-safe reference to a method.
15. What is a lambda expression?
A lambda expression is a short function syntax often used with LINQ and delegates.
16. What is LINQ?
LINQ is Language Integrated Query. It helps query collections and data sources using C# syntax.
ASP.NET Core Questions
17. What is ASP.NET Core?
ASP.NET Core is a modern framework for building web applications and APIs using .NET.
18. What is MVC?
MVC separates an application into Model, View and Controller responsibilities.
19. What is a Model?
A Model represents data and business rules used by the application.
20. What is a View?
A View displays the user interface.
21. What is a Controller?
A Controller handles requests, works with models and returns responses.
22. What is routing?
Routing maps incoming URLs to controllers, actions or endpoints.
23. What is dependency injection?
Dependency injection provides required objects to a class instead of creating them directly inside the class.
24. What is middleware?
Middleware is software in the request pipeline that can inspect, modify or pass requests and responses.
25. What is configuration?
Configuration stores settings such as connection strings, API keys and environment-specific values.
26. Authentication vs authorization?
Authentication verifies identity. Authorization decides what an authenticated user can access.
27. What are sessions?
Sessions store user-specific data for a limited time on the server side.
28. What is validation?
Validation checks whether user input follows expected rules before processing.
Entity Framework Core Questions
29. What is Entity Framework Core?
EF Core is an object-relational mapper that lets developers work with databases using C# objects.
30. What is DbContext?
DbContext represents a database session and is used to query and save data.
31. What is DbSet?
DbSet represents a table or collection of entities in the database.
32. What are migrations?
Migrations track database schema changes and apply them to the database.
33. What is Code First?
Code First means creating C# entity classes first and generating database schema from them.
34. What are relationships?
Relationships connect tables or entities, such as one-to-many between customer and orders.
35. What is CRUD?
CRUD means Create, Read, Update and Delete operations.
36. Eager loading vs lazy loading?
Eager loading loads related data immediately. Lazy loading loads related data only when accessed, if configured.
Web API Questions
37. What is REST API?
A REST API exposes resources over HTTP using methods such as GET, POST, PUT, PATCH and DELETE.
38. What is GET?
GET retrieves data from the server.
39. What is POST?
POST creates new data on the server.
40. What is PUT?
PUT usually replaces an existing resource.
41. What is PATCH?
PATCH partially updates an existing resource.
42. What is DELETE?
DELETE removes a resource.
43. What are HTTP status codes?
Status codes explain response results, such as 200 success, 201 created, 400 bad request, 401 unauthorized, 404 not found and 500 server error.
44. What is JSON?
JSON is a lightweight data format commonly used for API requests and responses.
45. What is a DTO?
A Data Transfer Object carries only the data needed between layers or API boundaries.
46. How do you test an API?
Use tools like Postman or browser dev tools to check URL, method, headers, request body and response.
SQL Server Questions
47. What is SELECT?
SELECT retrieves data from a table.
48. What is WHERE?
WHERE filters rows based on conditions.
49. GROUP BY vs HAVING?
GROUP BY groups rows. HAVING filters grouped results.
50. INNER JOIN vs LEFT JOIN?
INNER JOIN returns matching rows from both tables. LEFT JOIN returns all rows from the left table and matching rows from the right table.
51. Primary key vs foreign key?
A primary key uniquely identifies a row. A foreign key links a row to another table.
52. What is normalization?
Normalization organizes data to reduce duplication and improve consistency.
53. What are stored procedures?
Stored procedures are saved SQL routines that can be executed when needed.
54. What are indexes?
Indexes help improve query performance, but too many indexes can affect write operations.
55. What is a subquery?
A subquery is a query inside another query.
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HTML, CSS and JavaScript Questions
56. What are HTML forms?
Forms collect user input using controls such as text boxes, dropdowns and buttons.
57. What are CSS selectors?
Selectors choose HTML elements to style.
58. What are JavaScript variables?
Variables store values in JavaScript using var, let or const.
59. What are functions?
Functions group reusable logic.
60. What is the DOM?
The Document Object Model represents the page structure that JavaScript can read and change.
61. What are events?
Events are user or browser actions such as click, submit or keypress.
62. What is Fetch API?
Fetch API helps JavaScript call backend APIs and process responses.
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Git and GitHub Questions
63. What is a repository?
A repository stores project files and version history.
64. What is clone?
Clone copies a remote repository to your local system.
65. What are add, commit and push?
Add stages changes, commit saves them locally and push uploads them to the remote repository.
66. What are pull, branch and merge?
Pull gets remote changes, branch creates a separate line of work and merge combines changes.
67. What is a merge conflict?
A merge conflict happens when Git cannot automatically combine changes in the same part of a file.
.NET Scenario Questions
68. An ASP.NET Core application returns a 500 error. What would you check?
Check logs, exception details, recent code changes, configuration, database connection and deployment environment.
69. A Web API returns 401 Unauthorized. What could be wrong?
Authentication token, login status, authorization header, token expiry or API permission may be incorrect.
70. Entity Framework migration fails. What would you investigate?
Check connection string, migration files, model changes, database permissions and existing schema conflicts.
71. Data is not saving to SQL Server. What would you check?
Check validation errors, SaveChanges call, connection string, database permissions, exceptions and table constraints.
72. A SQL query is slow. What should you investigate?
Review joins, filters, indexes, execution plan, data volume and whether unnecessary columns are selected.
73. Login works locally but fails after deployment. What would you check?
Check environment settings, connection strings, cookies, HTTPS, domain, authentication configuration and logs.
74. Git merge conflict occurs. How would you handle it?
Open conflicted files, compare changes, choose the correct version, test the code, then add and commit the resolved file.
75. API works in Postman but not from the frontend. What would you investigate?
Check URL, HTTP method, CORS, headers, request body, browser console errors and authentication token.
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Final Preparation Tips
Revise basics daily, write small examples, practise SQL queries and explain your project flow from frontend to database. Keep answers honest. If you do not know something, explain what you would check and how you would debug it.
Quick Revision Table
| Area | Revise | Interview Focus |
|---|---|---|
| C# | OOP, collections, LINQ, exceptions | Write and explain simple code |
| ASP.NET Core | MVC, routing, DI, middleware | Explain request flow |
| EF Core | DbContext, migrations, CRUD | Connect code to database |
| SQL Server | joins, keys, indexes, queries | Retrieve and filter data |
| Frontend | forms, DOM, fetch, events | Connect UI to APIs |
More Scenario Questions
76. A page shows validation errors. What would you check?
Check model validation attributes, form fields, model binding, posted data and error messages.
77. A dropdown is empty on a form. What would you investigate?
Check database data, controller action, ViewBag or view model, query result and view binding.
78. A deployed app cannot connect to SQL Server. What could be wrong?
Connection string, firewall, credentials, server name, database permissions or environment settings may be wrong.
79. An API returns 404. What would you check?
Check route, controller name, action name, HTTP method and base URL.
80. JavaScript fetch fails. What would you check?
Check browser console, network tab, URL, method, CORS, headers and response body.
81. What should a fresher say if they do not know an answer?
Be honest, explain related basics and describe how you would search logs, documentation or code to debug.
More C# and ASP.NET Core Questions
82. What is access modifier?
An access modifier controls visibility of classes and members. Examples include public, private, protected and internal.
83. What is model binding?
Model binding maps incoming request data to action method parameters or model objects.
84. What is appsettings.json?
It is a configuration file commonly used to store settings such as connection strings and application options.
85. What is dependency injection lifetime?
It controls how long a service object lives, such as transient, scoped or singleton.
More EF Core and SQL Questions
86. What is a navigation property?
A navigation property represents a relationship between entities in EF Core.
87. What is SaveChanges?
SaveChanges writes tracked changes from DbContext to the database.
88. What is a SQL constraint?
A constraint enforces rules on table data, such as primary key, foreign key, unique or not null.
89. Why should SELECT * be avoided in many cases?
It can retrieve unnecessary columns, increase data transfer and make queries less clear.
More Full Stack Scenario Questions
90. A form submits but the controller receives null values. What would you check?
Check input names, model binding, form method, action URL, view model and validation errors.
91. A user can access an admin page. What should you verify?
Check authorization attributes, role assignment, login claims, route protection and test users.
92. An EF Core query returns duplicate rows. What would you inspect?
Check joins, relationships, Include usage, data duplication and query logic.
93. A page layout breaks on mobile. What would you check?
Check Bootstrap grid classes, CSS widths, media queries, images and browser dev tools.
94. A Git push is rejected. What could be the reason?
The remote branch may have new commits. Pull changes, resolve conflicts if any, then push again.
How Freshers Should Practise Answers
Do not memorize long definitions only. Pick one project and explain how data moves from HTML form to controller, validation, service, EF Core, SQL Server and response. Practise writing small SQL queries and C# examples. Interview confidence improves when you can connect definitions to your own project.