C Programming (101 Interview Questions)
1. Question: What is C programming language?
Answer: C is a general-purpose programming language developed in the early 1970s. It’s known for its efficiency and low-level memory manipulation capabilities.
2. Question: Explain the difference between “scanf” and “printf” in C.
Answer: “scanf” is used to read input from the user, while “printf” is used to display output to the screen.
3. Question: How are pointers used in C?
Answer: Pointers are variables that store memory addresses. They are used for dynamic memory allocation, efficient memory manipulation, and accessing data structures like arrays and linked lists.
4. Question: What is the significance of the “void” keyword in C?
Answer: “void” is used to indicate that a function doesn’t return a value or a variable doesn’t have a specific data type.
5. Question: How can you declare a constant variable in C?
Answer: You can use the “const” keyword before the variable declaration to make it a constant.
6. Question: What is the purpose of the “sizeof” operator in C?
Answer: The “sizeof” operator returns the size (in bytes) of a data type or a variable.
7. Question: Explain the difference between “while” and “do-while” loops in C.
Answer: “while” loop checks the condition before executing the loop, while “do-while” loop executes the loop at least once before checking the condition.
8. Question: What are preprocessor directives in C?
Answer: Preprocessor directives are commands that start with a “#” symbol. They are used for including header files, macro definitions, and conditional compilation.
9. Question: How can you allocate memory dynamically in C?
Answer: You can use functions like “malloc,” “calloc,” and “realloc” to allocate memory dynamically at runtime.
10. Question: Explain the “auto” storage class in C.
Answer: The “auto” storage class is used by default for local variables. It signifies that the variable’s lifetime is limited to the block in which it’s defined.
11. Question: What is the “volatile” keyword used for in C?
Answer: The “volatile” keyword indicates that a variable’s value can change at any time, even without any action being taken by the code.
12. Question: How do you swap the values of two variables without using a temporary variable?
Answer: You can use arithmetic or bitwise operations to swap the values of two variables without a temporary variable.
13. Question: Explain the concept of function pointers in C.
Answer: Function pointers are pointers that point to the memory address of a function. They allow functions to be passed as arguments to other functions or stored in data structures.
14. Question: What is a macro in C?
Answer: A macro is a preprocessor directive that defines a text substitution. Macros are often used for code reuse and to create shorthand notations.
15. Question: How do you define a structure in C?
Answer: A structure is defined using the “struct” keyword, followed by the structure’s name and its members enclosed in curly braces.
16. Question: What is the “typedef” keyword used for?
Answer: The “typedef” keyword is used to create aliases for existing data types, making code more readable and maintainable.
17. Question: Explain the concept of bitwise operators in C.
Answer: Bitwise operators manipulate individual bits of variables. Examples include AND (&), OR (|), XOR (^), left shift (<<), and right shift (>>).
18. Question: How do you create a multi-dimensional array in C?
Answer: You can create a multi-dimensional array by using multiple sets of square brackets. For example, “int myArray[3][4];” creates a 3×4 array.
19. Question: What is the purpose of the “break” statement in C?
Answer: The “break” statement is used to exit from loops and switch statements prematurely.
20. Question: Explain the concept of a header file in C.
Answer: A header file contains function prototypes, macro definitions, and declarations used to share information across multiple source code files.
21. Question: What is the difference between “malloc” and “calloc”?
Answer: Both functions are used to allocate memory dynamically, but “malloc” doesn’t initialize the memory, while “calloc” initializes the allocated memory to zero.
22. Question: How do you return multiple values from a function in C?
Answer: You can use pointers as function parameters to modify the values of variables outside the function’s scope.
23. Question: What is a pointer to a function in C?
Answer: A pointer to a function stores the memory address of a function. It can be used to call the function indirectly.
24. Question: Explain the “const” pointer in C.
Answer: A “const” pointer is a pointer whose value cannot be changed to point to another memory location. However, the data it points to can still be modified.
25. Question: What is the “static” keyword used for in C?
Answer: The “static” keyword has different meanings depending on the context. In the context of a local variable, it retains its value between function calls. In the context of a global variable, it restricts the variable’s scope to the current source file.
26. Question: What are the storage classes in C?
Answer: C has four storage classes: “auto,” “register,” “static,” and “extern.” These determine a variable’s lifetime, visibility, and storage location.
27. Question: How do you include a header file in C?
Answer: You can use the “#include” preprocessor directive followed by the name of the header file in angle brackets or double quotes.
28. Question: What is a “struct” in C?
Answer: A “struct” is a composite data type that groups variables of different types under a single name. It’s often used to represent a record.
29. Question: Explain the difference between “strcpy” and “strncpy” functions.
Answer: “strcpy” copies a string until the null-terminator, while “strncpy” allows you to specify a maximum number of characters to copy.
30. Question: What is the purpose of the “goto” statement?
Answer: The “goto” statement allows transferring control to a labeled statement within the same function. It’s generally discouraged due to its potential to make code less structured and harder to understand.
31. Question: How do you define a macro in C?
Answer: Macros are defined using the “#define” preprocessor directive followed by the macro name and its replacement text.
32. Question: What is the ternary operator in C?
Answer: The ternary operator (?:) is a shorthand way of writing an “if-else” statement in a single line.
33. Question: What is the purpose of the “sizeof” operator in C?
Answer: The “sizeof” operator is used to determine the size (in bytes) of a data type or a variable.
34. Question: How do you access command-line arguments in C?
Answer: Command-line arguments are passed to the “main” function as parameters. “argc” represents the number of arguments, and “argv” is an array of character pointers containing the argument values.
35. Question: Explain the purpose of the “enum” data type.
Answer: An “enum” is used to define a set of named integer constants. It provides a way to associate descriptive names with numeric values.
36. Question: What is the purpose of the “continue” statement?
Answer: The “continue” statement is used within loops to skip the current iteration and move to the next iteration.
37. Question: How do you open and close files in C?
Answer: The “fopen” function is used to open files, and the “fclose” function is used to close them. Files can be opened in various modes such as “r” (read), “w” (write), and “a” (append).
38. Question: Explain the concept of a “bitfield.”
Answer: A bitfield is a structure member that’s used to allocate a specific number of bits within a data type. It’s often used to conserve memory.
39. Question: What is the purpose of the “volatile” keyword in C?
Answer: The “volatile” keyword indicates that a variable can be modified by external entities, such as hardware or other threads, and the compiler should not optimize access to it.
40. Question: How do you perform dynamic memory deallocation in C?
Answer: The “free” function is used to release memory that was previously allocated using “malloc,” “calloc,” or “realloc.”
41. Question: What is the purpose of the “extern” keyword in C?
Answer: The “extern” keyword is used to declare a global variable or function that’s defined in a different source file.
42. Question: Explain the concept of recursion in C.
Answer: Recursion is a programming technique where a function calls itself to solve a problem. It involves a base case and a recursive case.
43. Question: What is a “null-terminated string” in C?
Answer: A null-terminated string is a sequence of characters followed by a null character (‘\0’). It’s used to represent strings in C.
44. Question: How can you read and write binary files in C?
Answer: To read binary files, you can use functions like “fread” and to write, you can use “fwrite.” These functions allow direct reading and writing of binary data.
45. Question: Explain the concept of a “union” in C.
Answer: A “union” is a composite data type that allows storing different types of data in the same memory location. However, only one member can hold a value at a time.
46. Question: What is a “header guard” in C?
Answer: A header guard is a preprocessor directive that prevents a header file from being included more than once in the same translation unit.
47. Question: How do you define a constant pointer in C?
Answer: A constant pointer is declared using the “const” keyword before the pointer’s data type.
48. Question: Explain the purpose of the “static” function in C.
Answer: A “static” function is only accessible within the source file where it’s defined. It’s used to encapsulate functionality and restrict its scope.
49. Question: What are the advantages of using “typedef” in C?
Answer: “typedef” provides a way to create custom type names, improving code readability and making it easier to update data types in the future.
50. Question: How do you compare strings in C?
Answer: You can use the “strcmp” function to compare two strings. It returns a value indicating whether the strings are equal, less than, or greater than each other.
51. Question: Explain the concept of “pointer arithmetic” in C.
Answer: Pointer arithmetic involves performing arithmetic operations on pointers. Adding an integer to a pointer advances it to the next element of the same data type.
52. Question: What is the purpose of the “volatile” qualifier?
Answer: The “volatile” qualifier indicates to the compiler that the value of a variable can change unexpectedly, even if no apparent modifications occur in the program.
53. Question: How can you create a linked list in C?
Answer: A linked list is created by defining a structure containing the data and a pointer to the next node. Nodes are dynamically allocated and connected using pointers.
54. Question: What is the significance of the “sizeof” operator when used with a structure?
Answer: When used with a structure, the “sizeof” operator returns the size of the entire structure, including its members and any padding added by the compiler.
55. Question: Explain the concept of “type casting” in C.
Answer: Type casting involves converting a value from one data type to another. It can be done implicitly or explicitly using casting operators.
56. Question: How can you reverse a linked list in C?
Answer: To reverse a linked list, you need to modify the pointers to reverse the direction of the links between nodes.
57. Question: What is the “volatile” keyword used for with pointers in C?
Answer: When “volatile” is used with a pointer, it indicates that the value the pointer points to is volatile and can change unexpectedly.
58. Question: What is the purpose of the “inline” keyword in C?
Answer: The “inline” keyword suggests to the compiler that a function’s code should be inserted directly into the calling code to improve performance.
59. Question: How do you use the “malloc” function to allocate memory for an array?
Answer: You can use “malloc” to allocate memory for an array by specifying the total number of bytes required for the array.
60. Question: Explain the purpose of the “restrict” keyword in C.
Answer: The “restrict” keyword is a type qualifier that tells the compiler that a pointer is the only way to access a specific memory location, allowing for optimization.
61. Question: What is a “memory leak” in C?
Answer: A memory leak occurs when allocated memory isn’t properly deallocated, leading to a gradual loss of available memory.
62. Question: How can you find the length of a string in C?
Answer: The “strlen” function is used to determine the length of a null-terminated string.
63. Question: Explain the “volatile” keyword in the context of multi-threading.
Answer: In a multi-threaded environment, the “volatile” keyword is used to ensure that the compiler doesn’t optimize away memory reads or writes, preventing unexpected behavior due to thread interactions.
64. Question: How can you implement a stack using an array in C?
Answer: A stack can be implemented using an array, where elements are pushed onto the top and popped off from the top using index manipulation.
65. Question: What is the purpose of the “exit” function in C?
Answer: The “exit” function is used to terminate a program and return an exit status to the operating system.
66. Question: Explain the “const” pointer in the context of function parameters.
Answer: In the context of function parameters, a “const” pointer means that the pointer itself is constant and cannot be used to modify the pointed-to data.
67. Question: How do you declare a two-dimensional array using pointers?
Answer: You can declare a two-dimensional array using pointers as follows: int (*arr)[columns];
68. Question: What is the purpose of the “enum” keyword in C?
Answer: The “enum” keyword is used to define a new data type that consists of a set of named integer constants.
69. Question: How can you perform file I/O using “fprintf” and “fscanf”?
Answer: “fprintf” is used to write formatted data to a file, while “fscanf” is used to read formatted data from a file.
70. Question: Explain the “do-while” loop in C.
Answer: The “do-while” loop executes the loop body at least once before checking the loop condition.
71. Question: What is the “offsetof” macro used for?
Answer: The “offsetof” macro calculates the offset of a member within a structure.
72. Question: How can you implement a queue using pointers in C?
Answer: A queue can be implemented using pointers by maintaining a linked list and having pointers to the front and rear of the queue.
73. Question: What is the purpose of the “strcmp” function?
Answer: The “strcmp” function is used to compare two strings and returns a value indicating whether they are equal or not.
74. Question: Explain the “for” loop in C.
Answer: The “for” loop is used for repetitive tasks and consists of an initialization, a condition, an update, and a loop body.
75. Question: How do you handle memory allocation errors when using “malloc”?
Answer: You can check if the returned pointer from “malloc” is NULL, which indicates a memory allocation failure.
76. Question: What is the purpose of the “const” qualifier in function declarations?
Answer: The “const” qualifier in function declarations indicates that the function does not modify the input parameters.
77. Question: Explain the concept of “file pointers” in C.
Answer: A file pointer is a data structure used to keep track of the current position in a file during reading or writing operations.
78. Question: How can you swap the values of two variables using XOR?
Answer: You can use XOR bitwise operations to swap the values of two variables without using additional memory.
79. Question: What is a “self-referential structure” in C?
Answer: A self-referential structure is a structure that contains a pointer to an instance of the same structure type.
80. Question: How do you create a header file and use it in multiple source files?
Answer: To create a header file, define function prototypes and include guards, then use the “#include” directive to include it in multiple source files.
81. Question: Explain the concept of “endianness” in C.
Answer: Endianness refers to the order of bytes in a multi-byte data type. In “big-endian,” the most significant byte comes first; in “little-endian,” the least significant byte comes first.
82. Question: What are “function prototypes” in C?
Answer: Function prototypes provide information about the function’s name, return type, and parameter types. They are used to declare functions before they are defined.
83. Question: How do you use “const” with pointers in C?
Answer: You can use “const” to declare a pointer to a constant variable, a constant pointer, or a constant pointer to a constant variable.
84. Question: Explain the purpose of the “continue” statement in a loop.
Answer: The “continue” statement skips the current iteration of a loop and continues with the next iteration.
85. Question: How do you implement a binary search in C?
Answer: Binary search involves dividing a sorted array in half and comparing the target value with the middle element to eliminate half of the remaining values.
86. Question: What is the difference between “realloc” and “free”?
Answer: “realloc” is used to resize a dynamically allocated memory block, while “free” is used to release memory back to the system.
87. Question: Explain the concept of a “multidimensional pointer” in C.
Answer: A multidimensional pointer is a pointer that points to a block of memory containing elements of a multidimensional array.
88. Question: How do you define a constant string in C?
Answer: A constant string can be defined using the “const” keyword before the string declaration.
89. Question: Explain the difference between “return 0” and “return EXIT_SUCCESS.”
Answer: “return 0” and “return EXIT_SUCCESS” are both used to indicate successful program termination, but “EXIT_SUCCESS” is a macro defined in the standard library.
90. Question: How do you implement a bubble sort algorithm in C?
Answer: Bubble sort involves repeatedly stepping through the list, comparing adjacent elements, and swapping them if they’re in the wrong order.
91. Question: What is the “calloc” function used for?
Answer: The “calloc” function allocates memory for an array and initializes the memory to zero.
92. Question: Explain the concept of “recursion termination” in recursive functions.
Answer: Recursion termination refers to the base case of a recursive function, where the function stops calling itself and returns a result.
93. Question: How can you concatenate two strings in C?
Answer: You can use the “strcat” function to concatenate two strings. The destination string should have enough space to hold both strings.
94. Question: What is a “trailing comma” in C?
Answer: A trailing comma is a comma that appears after the last element in an initializer list, which is allowed in C.
95. Question: Explain the “modulus” operator (%) in C.
Answer: The modulus operator (%) returns the remainder of a division operation. For example, “a % b” gives the remainder when “a” is divided by “b.”
96. Question: What is the purpose of the “offsetof” macro in C?
Answer: The “offsetof” macro is used to calculate the offset of a structure member from the beginning of the structure.
97. Question: How can you implement a quicksort algorithm in C?
Answer: Quicksort involves selecting a pivot element and partitioning the array into two sub-arrays such that elements less than the pivot are on one side and greater on the other.
98. Question: Explain the “strncpy” function in C.
Answer: “strncpy” is used to copy a specified number of characters from one string to another, potentially preventing buffer overflow.
99. Question: How can you define a global variable that can be accessed across multiple source files?
Answer: By declaring the variable as “extern” in one source file and then defining it without “extern” in another source file.
100. Question: What is the “sizeof” operator used for with structures in C?
Answer: The “sizeof” operator returns the size in bytes of a structure, including its members and any padding added by the compiler.
101. Question: How can you reverse a string in C?
Answer: You can reverse a string by swapping characters from the start to the middle of the string until the whole string is reversed.