Interview questions in C, Java and Python

 

C Programming Interview Questions (30+ Questions)

Basic C Questions

1. What is C language?
• C is a procedural, mid-level programming language developed by Dennis Ritchie in 1972.
2. What are the key features of C?
• Portability, efficiency, modularity, and low-level memory access.
3. What is a pointer in C?
• A pointer is a variable that stores the memory address of another variable.
4. What is the difference between malloc() and calloc()?
• malloc() allocates memory without initialization, while calloc() initializes memory to zero.
5. What is the use of static keyword in C?
• It retains the value of a variable between function calls and limits scope to the file (for global variables).
6. Explain const keyword in C.
• It makes a variable read-only (immutable).
7. What is a dangling pointer?
• A pointer pointing to a deallocated memory location.
8. What is recursion? Give an example.
• A function calling itself (e.g., factorial calculation).
9. Difference between ++i and i++?
• ++i is pre-increment, i++ is post-increment.
10. What is a header file in C?
• Contains function declarations and macros (e.g., stdio.h).

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Intermediate C Questions

11. What is a structure in C?
• A user-defined data type that groups different data types.
12. What is a union in C?
• Similar to a structure but shares memory for all members.
13. What is the difference between struct and union?
• Struct allocates separate memory for each member; union shares memory.
14. What is typedef in C?
• Used to create an alias for a data type.
15. What is volatile keyword in C?
• Prevents compiler optimization for variables that may change unexpectedly.
16. What is a memory leak?
• When dynamically allocated memory is not freed, causing wasted memory.
17. What is #pragma in C?
• A compiler directive for special instructions.
18. Explain sizeof() operator.
• Returns the size (in bytes) of a variable or data type.
19. What is a function pointer?
• A pointer that points to a function instead of a variable.
20. What is strtok() in C?
• Used to split strings into tokens.

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Advanced C Questions

21. What is the difference between memcpy() and memmove()?
• memmove() handles overlapping memory regions; memcpy() does not.
22. What is a far pointer?
• Used in segmented architectures to access memory outside the current segment.
23. What is a null pointer?
• A pointer that does not point to any valid memory location (NULL).
24. What is a void pointer?
• A generic pointer that can point to any data type.
25. What is the difference between #include <file.h> and #include "file.h"?
• <file.h> searches in system directories, "file.h" searches in local directories.
26. What is a bit field in C?
• A data structure that stores data in bits.
27. What is restrict keyword in C?
• Indicates that a pointer is the only way to access the memory it points to.
28. What is setjmp() and longjmp()?
• Used for non-local jumps in C.
29. What is a file descriptor in C?
• An integer representing an open file.
30. What is errno in C?
• A global variable indicating error codes.

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Java Programming Interview Questions (40+ Questions)

Basic Java Questions

31. What is Java?
• An object-oriented, platform-independent programming language.
32. What is JVM?
• Java Virtual Machine executes Java bytecode.
33. Difference between JDK, JRE, and JVM?
• JDK (Development Kit), JRE (Runtime Environment), JVM (Execution Engine).
34. What is the main method in Java?
• Entry point of a Java program (public static void main(String[] args)).
35. What are Java access modifiers?
• public, private, protected, and default (package-private).
36. What is method overloading?
• Multiple methods with the same name but different parameters.
37. What is method overriding?
• Redefining a parent class method in a child class.
38. What is the final keyword in Java?
• Makes a variable constant, a method non-overridable, or a class non-inheritable.
39. What is a constructor?
• A special method called when an object is created.
40. What is the difference between == and .equals()?
• == checks reference, .equals() checks content.

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Intermediate Java Questions

41. What is the difference between String, StringBuilder, and StringBuffer?
• String is immutable, StringBuilder is mutable & not thread-safe, StringBuffer is thread-safe.
42. What is exception handling in Java?
• Using try-catch-finally blocks to handle runtime errors.
43. What are checked and unchecked exceptions?
• Checked (compile-time, e.g., IOException), Unchecked (runtime, e.g., NullPointerException).
44. What is multithreading in Java?
• Running multiple threads simultaneously.
45. Difference between extends and implements?
• extends for inheritance, implements for interfaces.
46. What is a singleton class?
• A class that allows only one instance.
47. What is the static keyword in Java?
• Belongs to the class rather than instances.
48. What is garbage collection in Java?
• Automatic memory management by JVM.
49. What are Java collections?
• Frameworks like List, Set, Map, etc.
50. Difference between ArrayList and LinkedList?
• ArrayList is array-based, LinkedList uses nodes.

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Advanced Java Questions

51. What is reflection in Java?
• Inspecting and modifying classes at runtime.
52. What is Java generics?
• Allows type-safe collections (e.g., ArrayList<String>).
53. What is a Java annotation?
• Metadata added to code (e.g., @Override).
54. What is the Java memory model?
• Defines how threads interact through memory.
55. What is volatile in Java?
• Ensures variable visibility across threads.
56. What is the transient keyword?
• Excludes a field from serialization.
57. What is serialVersionUID?
• A version control number for serialization.
58. What is a Java lambda expression?
• A concise way to implement functional interfaces.
59. What is the Java Stream API?
• Used for functional-style operations on collections.
60. What is the Optional class in Java?
• Avoids NullPointerException by wrapping nullable objects.

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Python Programming Interview Questions (30+ Questions)

Basic Python Questions

61. What is Python?
• An interpreted, high-level, dynamically typed language.
62. What are Python’s key features?
• Easy syntax, dynamic typing, extensive libraries.
63. What are Python lists and tuples?
• Lists are mutable, tuples are immutable.
64. What is a Python dictionary?
• A key-value pair collection ({}).
65. What is PEP 8?
• Python’s style guide for clean code.
66. What is __init__ in Python?
• Constructor method for classes.
67. What is a lambda function?
• An anonymous function (lambda x: x+1).
68. What is list comprehension?
• Concise way to create lists ([x for x in range(10)]).
69. What is the difference between == and is?
• == checks value, is checks memory location.
70. What are Python decorators?
• Functions that modify other functions (@decorator).

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Intermediate Python Questions

71. What is the GIL in Python?
• Global Interpreter Lock restricts multi-threading.
72. What are Python generators?
• Functions that yield values lazily (yield keyword).
73. What is *args and **kwargs?
• *args for variable arguments, **kwargs for keyword arguments.
74. What is pickle in Python?
• Used for object serialization.
75. What is __str__ vs __repr__?
• __str__ for user-friendly output, __repr__ for debugging.
76. What is zip() in Python?
• Combines multiple iterables.
77. What is map() and filter()?
• map() applies a function, filter() filters elements.
78. What is a Python module?
• A file containing Python code (import module).
79. What is virtualenv?
• Creates isolated Python environments.
80. What is try-except-else-finally?
• Handles exceptions in Python.

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Advanced Python Questions

81. What is monkey patching?
• Modifying classes/modules at runtime.
82. What is a Python metaclass?
• A class that defines other classes (type).
83. What is asyncio in Python?
• Library for asynchronous programming.
84. What is collections.defaultdict?
• A dictionary with default values.
85. What is __slots__?
• Optimizes memory usage in classes.
86. What is @staticmethod vs @classmethod?
• @staticmethod doesn’t take self, @classmethod takes cls.
87. What is functools.partial?
• Freezes some function arguments.
88. What is __call__ in Python?
• Makes an object callable like a function.
89. What is __new__ vs __init__?
• __new__ creates an object, __init__ initializes it.
90. What is contextlib?
• Helps in creating context managers.