C Fundamentals

1. What is C?

   • C is a general-purpose, procedural programming language known for its efficiency and portability.
   • It's widely used for system programming, embedded systems, and game development.

2. What are the key features of C?

   • Low-level access: Provides direct control over hardware and memory.
   • Efficiency: Known for its speed and performance.
   • Portability: Can be compiled and run on various operating systems.
   • Widely used: A foundational language for many other programming languages.

3. What is the difference between C and C++?

   • C: Procedural programming language.
   • C++: Object-oriented programming language, built upon C, with features like classes, objects, and inheritance.

4. Explain the concept of pointers in C.

   • Variables that store memory addresses of other variables.
   • Enable direct manipulation of memory.

5. What are data types in C?

   • Primitive data types: int, float, double, char, void
   • Derived data types: Arrays, structures, unions, pointers

Control Flow

6. Explain conditional statements in C (if, else, else if).

   • Used to execute different blocks of code based on conditions.

7. Explain loops in C (for, while, do-while).

   • for: Iterates a specific number of times.
   • while: Executes a block of code as long as a condition is true.
   • do-while: Executes a block of code at least ¹ once, then repeats as long as a condition is true.  
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8. What is the purpose of the break and continue statements?

   • break: Exits the current loop.
   • continue: Skips the current iteration and moves to the next.

Functions

9. How do you define a function in C?

   • return_type function_name(parameters)

10. What are arguments and parameters in C functions?

    • Parameters: Variables defined within the function's definition.
    • Arguments: Values passed to the function when it's called.

11. What is the purpose of the return statement?

    • Used to return a value from a function.

12. Explain the concept of recursion in C.

    • A function that calls itself directly or indirectly.

Pointers

13. What is the difference between a pointer and a reference?

    • Pointer: Stores the memory address of a variable.
    • Reference: An alias for an existing variable.

14. How do you declare a pointer in C?

    • data_type *pointer_name;

15. What is the difference between * and & operators?

    • *: Dereference operator (gets the value at the memory address).
    • &: Address-of operator (gets the memory address of a variable).

16. What is pointer arithmetic?

    • Performing arithmetic operations on pointers to move them to different memory locations.

Arrays

17. Explain how arrays are declared and accessed in C.

    • data_type array_name[size];

18. What are multidimensional arrays in C?

    • Arrays with more than one dimension (e.g., two-dimensional arrays for representing matrices).

Structures

19. What are structures in C?

    • User-defined data types that group together variables of different data types.

20. How do you define and access members of a structure?

    • Use the dot (.) operator to access members of a structure.

Strings

21. How are strings represented in C?

    • Typically represented as an array of characters, terminated by a null character (\0).

22. What are some common string manipulation functions in C?

    • strcpy(), strcat(), strlen(), strcmp()

File Handling

23. How do you open a file in C?

    • FILE *fp = fopen("filename", "mode"); (e.g., "r" for reading, "w" for writing)

24. How do you read data from a file in C?

    • fscanf(fp, "%d", &variable);

25. How do you write data to a file in C?

    • fprintf(fp, "%d", variable);

Memory Management

26. What is dynamic memory allocation in C?

    • Allocating memory at runtime using functions like malloc() and calloc().

27. What is the purpose of malloc() and free() functions?

    • malloc(): Allocates a block of memory dynamically.
    • free(): Releases dynamically allocated memory.

Preprocessor Directives

28. What are preprocessor directives in C?

    • Instructions for the compiler that are processed before the actual compilation.

29. What is the #include directive?

    • Includes the contents of a header file into the source code.

30. What is the #define directive?

    • Defines a macro, which can be used to replace a constant with a value.

Bitwise Operators

31. What are bitwise operators in C?
    • Operators that work on individual bits of data (e.g., & (AND), | (OR), ^ (XOR), ~ (NOT), << (left shift), >> (right shift)).

Pointers to Functions

32. What are pointers to functions in C?
    • Pointers that store the memory address of a function.

Data Structures

33. What are linked lists in C?

    • A linear data structure where each element (node) points to the next.

34. What are trees in C?

    • Hierarchical data structures where each node has zero or more child nodes.

35. What are stacks and queues in C?

    • Stack: A LIFO (Last-In, First-Out) data structure.
    • Queue: A FIFO (First-In, First-Out) data structure.

Input/Output

36. What is standard input, standard output, and standard error?
    • Standard input: Typically the keyboard.
    • Standard output: Typically the console.
    • Standard error: Used for displaying error messages.

Debugging

37. How can you debug C programs?
    • Use a debugger (e.g., GDB) to step through the code, inspect variables, and identify errors.

Testing

38. What are unit tests and why are they important?
    • Test individual units of code (e.g., functions) to ensure they work as expected.
    • Improve code quality and reduce the risk of bugs.

Advanced Topics

39. What is dynamic memory allocation and why is it important?

    • Allows you to allocate memory at runtime based on the program's needs.

40. What are file I/O operations in C?

    • Reading from and writing to files.

41. What is the difference between a structure and a union in C?

    • Structure: All members are allocated memory contiguously.
    • Union: Only enough memory is allocated for the largest member.

42. What is the purpose of the typedef keyword?

    • Creates a new name for an existing data type.

Interview Questions

43. Explain the difference between C and C++.
44. How would you implement a linked list in C?
45. Write a C program to find the factorial of a number.
46. Explain the concept of pointers to functions and give an example.
47. How would you handle memory leaks in a C program?
48. Describe the process of compiling and linking a C program.
49. What are some of the best practices for writing C code?
50. How would you debug a segmentation fault in a C program?

I hope these questions are helpful for your C interview preparation!