C Programming — Complete Notes + 50 MCQs

SEO-friendly, mobile-ready page with clean UI. Correct answers highlighted.

Overview

C is a general-purpose, procedural programming language developed by Dennis Ritchie at Bell Labs in the early 1970s. It provides low-level access to memory, efficient mapping to machine instructions, and is widely used for system programming, embedded systems, and performance-critical applications.

Why learn C?

Foundation for many languages (C++, C#, Java)
Fine-grained control of memory (pointers)
Lightweight runtime and efficient execution
Essential for systems programming and embedded devices

Fundamental Concepts

Syntax & Structure

A C program consists of functions and declarations. Execution begins at main(). Statements end with semicolons.

// basic structure
#include <stdio.h>

int main(void) {
  printf("Hello, world!\n");
  return 0;
}

Data Types & Variables

Primary types: int, char, float, double. Use sizeof() to find storage size. Qualifiers: short, long, signed, unsigned.

Operators

Arithmetic, relational, logical, bitwise, assignment, and ternary (?:) operators. Precedence matters; use parentheses to clarify.

Control Flow

Conditional statements: if, if-else, switch. Loops: for, while, do-while. Use break and continue.

Functions

Declare prototypes, define functions, pass by value (C passes arguments by value). For arrays/large data, pass pointers.

int add(int a, int b) { return a + b; }

Arrays & Strings

Arrays: contiguous memory for elements of same type. Strings are arrays of char terminated by '\0'. Use functions in <string.h> like strcpy, strlen.

Pointers

A pointer stores memory address. Pointer arithmetic, dereference (*), address operator (&). Pointers to pointers and function pointers exist. Understand NULL and pointer safety.

int x=10; int *p = &x; printf("%d", *p); // prints 10

Structures & Unions

struct groups related variables; union shares memory for members. Use typedef for readability.

Dynamic Memory

Use malloc, calloc, realloc and free memory with free(). Avoid memory leaks and dangling pointers.

File I/O

Use fopen, fclose, fread, fwrite, fprintf, fscanf. Check for NULL file pointers.

Preprocessor

Directives: #include, #define, #ifdef. Used for macros and conditional compilation.

Compilation & Debugging

Compile: gcc -o prog prog.c. Compilation stages: preprocessing, compilation, assembly, linking. Use -Wall to enable warnings. Debug using gdb or printf debugging, and tools like Valgrind for memory issues.

Best Practices

Initialize variables before use.
Check return values (e.g., file opens, malloc).
Avoid magic numbers — use named constants.
Free dynamically allocated memory.
Write modular code and keep functions small and single-purpose.

50 Practice MCQs — Correct answers highlighted

1. Who developed the C programming language?

A) Bjarne Stroustrup
B) Dennis Ritchie ✅
C) James Gosling
D) Ken Thompson

2. Which function is the entry point of a C program?

A) start()
B) main() ✅
C) init()
D) program()

3. Which header file is required for printf?

A) <stdio.h> ✅
B) <stdlib.h>
C) <string.h>
D) <math.h>

4. Which of the following is a valid variable name in C?

A) 2count
B) count2 ✅
C) #value
D) void

5. Size of int on a typical 32-bit system is:

A) 1 byte
B) 4 bytes ✅
C) 8 bytes
D) 2 bytes

6. What does the '*' operator denote in declarations like int *p;?

A) Pointer to int ✅
B) Multiplication
C) Dereference
D) Address of

7. String in C is terminated by:

A) '0'
B) '\0' (null character) ✅
C) '\n'
D) EOF

8. Which declaration declares an array of 10 integers?

A) int a[10]; ✅
B) int a();
C) int a{10};
D) int 10[a];

9. By default, arguments in C are passed by:

A) Value ✅
B) Reference
C) Pointer only
D) Shared memory

10. Which function allocates memory dynamically?

A) malloc() ✅
B) free()
C) alloc()
D) new()

11. Which function releases memory allocated by malloc?

A) free() ✅
B) delete()
C) release()
D) freeall()

12. What does sizeof(char) typically return?

A) 1 ✅
B) 2
C) 4
D) Depends on OS

13. Which directive includes a header file?

A) #include ✅
B) #define
C) #ifdef
D) #pragma

14. What is typedef used for?

A) Create type aliases ✅
B) Define constants
C) Inline functions
D) Comment code

15. How do you access members of a struct through pointer p?

A) p->member ✅
B) p.member
C) (*p).member
D) Both A and C ✅

16. An enum in C is used to:

A) Create functions
B) Define named integer constants ✅
C) Define arrays
D) Allocate memory

17. What is NULL?

A) Uninitialized pointer
B) Pointer with value zero ✅
C) Pointer to code
D) End of file marker

18. Which operator gives the address of a variable?

A) & ✅
B) *
C) ->
D) %

19. Which has higher precedence?

A) Multiplication (*) over Addition (+) ✅
B) Addition over Multiplication
C) Both equal
D) Depends on compiler

20. Which loop will execute body at least once?

A) for
B) while
C) do-while ✅
D) None

21. Which function reads formatted input from stdin?

A) scanf() ✅
B) gets()
C) fgets()
D) read()

22. What is the format specifier for double?

A) %f
B) %lf ✅
C) %d
D) %c

23. fopen with mode "r" does what?

A) Opens file for reading ✅
B) Opens for writing
C) Appends
D) Reads and writes

24. Standard error stream is:

A) stderr ✅
B) stdin
C) stdout
D) stdlog

25. A macro is defined using:

A) #define ✅
B) typedef
C) #include
D) #pragma

26. The qualifier 'const' means:

A) The variable is read-only ✅
B) Variable is volatile
C) Variable is static
D) Variable is extern

27. Static variable inside a function retains its value between calls. True or false?

A) True ✅
B) False
C) Depends on compiler
D) Only for global

28. Which operator performs bitwise AND?

A) & ✅
B) &&
C) |
D) ^

29. sizeof operator returns size in:

A) Bytes ✅
B) Bits
C) Words
D) Kilobytes

30. volatile keyword tells compiler that variable may change unexpectedly. This prevents optimization. True or false?

A) True ✅
B) False
C) Only for globals
D) Only for pointers

31. In old C, function declarations without return type defaulted to int. Modern compilers warn against this. True?

A) True ✅
B) False
C) Depends on standard
D) Only in C++

32. A function pointer can be used to:

A) Call different functions at runtime ✅
B) Allocate memory
C) Define macros
D) Replace structs

33. Recursion is:

A) A function calling itself ✅
B) Loop unrolling
C) Pointer arithmetic
D) Dynamic allocation

34. Segmentation fault often occurs due to:

A) Invalid memory access (e.g., dereferencing NULL) ✅
B) Syntax error
C) Linker error
D) IO error

35. Linker stage does:

A) Resolve external references and combine object files ✅
B) Convert source to assembly
C) Execute program
D) Preprocess code

36. Which header provides malloc and free?

A) <stdlib.h> ✅
B) <stdio.h>
C) <string.h>
D) <math.h>

37. getchar() reads from:

A) stdin ✅
B) stdout
C) stderr
D) File

38. Pointer arithmetic increments by size of pointed type. True or false?

A) True ✅
B) False
C) Only on 32-bit
D) Only for char*

39. fopen mode "w" will:

A) Create file for writing (truncate if exists) ✅
B) Open for reading
C) Append only
D) Read+write without truncate

40. Macro vs function: macro is expanded by preprocessor. True or false?

A) True ✅
B) False
C) Macros are runtime
D) Functions are preprocessed

41. sizeof returns size for types and expressions. It is evaluated at compile time for types. True?

A) True ✅
B) False
C) Only for built-ins
D) Only for variables

42. Implicit type conversion is called:

A) Coercion ✅
B) Casting
C) Promotion
D) Demotion

43. Left shifting 1 by 3 (1<<3) gives:

A) 8 ✅
B) 3
C) 4
D) Undefined

44. errno is used to:

A) Report error codes from system calls ✅
B) Store last printf output
C) Track memory usage
D) Manage file descriptors

45. Undefined behavior in C means compiler may do anything. True or false?

A) True ✅
B) False
C) It prints error
D) It is runtime exception

46. Reentrant function is safe to call from signal handlers. True?

A) True ✅
B) False
C) Only for static
D) Only for globals

47. Which header provides fixed width integer types like int32_t?

A) <stdint.h> ✅
B) <inttypes.h>
C) <stddef.h>
D) <limits.h>

48. fflush(stdout) is used to:

A) Flush output buffer ✅
B) Close stream
C) Read from stream
D) Clear stdin

49. exit(0) indicates successful termination. True?

A) True ✅
B) False
C) exit(-1) is success
D) Depends on OS

50. Which function compares two memory blocks?

A) memcmp() ✅
B) strcmp()
C) memcpy()
D) memset()