rukmini santoshi

Posted on Nov 24

Top C MCQs Every Student Must Master Before Interviews

#c #mcqs #viva #clanguage

If you are preparing for technical interviews in 2025, you’ve probably realized one thing: C MCQs are no longer “just theory.” Companies use them to judge how well you understand logic, memory behavior, pointers, and the tiny details that differentiate an average programmer from an industry-ready one. This can feel overwhelming, especially when interview MCQs expose gaps you didn’t know existed.

Many students study syntax but struggle when those same concepts appear in tricky multiple-choice questions. Why does a simple increment operator behave differently? Why does a missing header break the entire code? Why does pointer arithmetic confuse even those who code daily? If you’ve asked these questions, you’re exactly where most candidates stand before interviews.

This guide gives you a mentor-style walkthrough of the most essential C MCQs you must master for placements in 2025, handpicked, simplified, and fully explained from basics to advanced concepts. By the end, you won’t just memorize answers; you’ll understand how C behaves under the hood so you can solve exam questions, debug code confidently, and impress in interviews.

Let’s get you technically sharp, step by step.

Foundational C MCQs Every Beginner Should Know (Basics)

These are the MCQs interviewers use to test your foundational clarity. They look simple, but they reveal how strong your basics really are.

Which of the following is a correctly written variable name in C?
a) 1num
b) num-1
c) value_1
d) int
Answer: c) value_1
Explanation: Identifiers must start with a letter/underscore and cannot contain symbols like hyphens.
Which of these represents a valid comment format in C?
a) // comment
b) /* comment /
c) # comment
d) Both a and b
Answer: d) Both a and b
Explanation: C allows both single-line (//) and multi-line (/ */) comments.
How do you access members of a structure stored in a variable (not pointer)?
a) ->
b) .
c) ::
d) :
Answer: b) .
Explanation: The dot operator accesses members when you have a normal structure variable.
What will printf("%d", x++); print when x = 5?
a) 6
b) 5
c) Undefined
d) Error
Answer: b) 5
Explanation: Post-increment returns the current value, then increments afterward.
Which data types can store decimal values in C?
a) int
b) double
c) float
d) Both b and c
Answer: d) Both b and c
Explanation: float and double support fractional values.
Which symbol is used for a bitwise AND operation?
a) &&
b) &
c) |
d) ^
Answer: b) &
Explanation: & performs bit-level AND; && is logical AND.
The XOR (exclusive OR) operator in C is represented by:
a) ^
b) ~
c) &&
d) |
Answer: a) ^
Which operator flips every bit in an integer?
a) ~
b) &
c) ^
d) !
Answer: a) ~
Explanation: The bitwise NOT operator toggles all bits.
Which statement exits the nearest loop immediately?
a) continue
b) break
c) exit()
d) skip
Answer: b) break
Select the correct syntax for a do-while loop:
a) do { } while (condition);
b) while() { } do
c) do(condition) {}
d) repeat {} until(condition);
Answer: a)
Which keyword jumps to a labeled part of the program?
a) goto
b) break
c) jump
d) next
Answer: a) goto
How many times will this print?
for (;;) { if(i==2) break; printf("%d", i++); }

a) 0 1 2
b) 0 1
c) Infinite
d) 1 2
Answer: b) 0 1

Which function is mandatory in every C program?
a) start()
b) main()
c) entry()
d) init()
Answer: b) main()
Header files in C typically use which extension?
a) .c
b) .exe
c) .h
d) .bin
Answer: c) .h
Which of the following is a valid function prototype for returning float and taking two ints?
a) float f(int, int);
b) float f(a, b);
c) float f(int a, int b);
d) Both a and c
Answer: d)
Where is a global variable declared?
a) Inside a function
b) Outside all functions
c) Inside main()
d) In a loop
Answer: b)
Which represents a character constant?
a) 'A'
b) "A"
c) 65
d) A
Answer: a)
Which keyword ensures a variable cannot be modified?
a) const
b) static
c) register
d) immutable
Answer: a) const
Which storage class is automatically applied to local variables?
a) auto
b) static
c) extern
d) register
Answer: a) auto
Which is a valid identifier?
a) 1data
b) data-point
c) dataset
d) char constant
Answer: c) dataset
Which preprocessor directive defines a constant/macro?
a) #include
b) #define
c) #ifdef
d) #pragma
Answer: b) #define
The #include directive is used to:
a) Define macros
b) Add header/source files
c) Start execution
d) Allocate memory
Answer: b)
Which directive checks whether a macro exists before compiling code?
a) #ifdef
b) #define
c) #include
d) #pragma
Answer: a) #ifdef
Which statement about identifiers is correct?
a) They may include spaces
b) They cannot be keywords
c) They must start with numbers
d) They can contain hyphens
Answer: b)
What does the sizeof operator return?
a) Number of variables
b) Total memory used by program
c) Size of data type/variable in bytes
d) Index count
Answer: c)

*Quick Note *
Most companies now start interviews with quick MCQs to immediately judge your comfort with the language before moving to coding rounds.

Bottom Line
Mastering basics prevents silly mistakes that can cost you marks in exams and confidence in interviews.

Intermediate MCQs Every Interview Panel Expects You to Know

These MCQs test practical understanding, memory allocation, headers, control flow, and operator precedence.

What is the purpose of sizeof?
a) Returns array length
b) Returns memory needed for a type
c) Returns RAM usage
d) Counts elements
Answer: b)
What will this print?
int x=10, y=20; printf("%d", x+y);
a) 20
b) 10
c) 30
d) None
Answer: c)
malloc() and free() are declared in which header?
a) string.h
b) stdio.h
c) stdlib.h
d) memory.h
Answer: c)
If a function has no return type mentioned, what is assumed?
a) void
b) int
c) char
d) float
Answer: b)
Which operator represents logical AND?
a) &
b) &&
c) and
d) ||
Answer: b)
Which header is required for printf and scanf?
a) stdlib.h
b) stdio.h
c) conio.h
d) math.h
Answer: b)
Function to read a single character from standard input:
a) scanf
b) getchar
c) gets
d) putchar
Answer: b)
Which function computes power values?
a) sqrt
b) pow
c) exp
d) abs
Answer: b)
Mathematical functions like sin() require:
a) stdio.h
b) math.h
c) string.h
d) time.h
Answer: b)
Keyword used to define an enum:
a) struct
b) enum
c) typedef
d) define
Answer: b)
What does typedef do?
a) Creates a new type alias
b) Allocates memory
c) Removes variables
d) Converts types
Answer: a)
Output?
typedef int num; num a=5; printf("%d", a);
a) 0
b) 5
c) Error
d) Undefined
Answer: b)
Correct float declaration:
a) float value;
b) int value;
c) float value="2.3";
d) double value;
Answer: a)
Equality check operator is:
a) =
b) ==
c) !=
d) :=
Answer: b)
Solve: 5 + 2 * 3
a) 21
b) 11
c) 17
d) 27
Answer: b)
Operator giving size in bytes:
a) size()
b) sizeof
c) length
d) bytes()
Answer: b)
Increment operator is:
a) ++
b) +=
c) --
d) **
Answer: a)
Which loop is nested?
a) for(i) for(j)
b) for(i)
c) while(1)
d) if(a>b)
Answer: a)
Labels in C must:
a) Be inside main only
b) Be unique inside a function
c) Start with #
d) Be global
Answer: b)
Correct enum usage:
a) enum color {RED}; enum color c=RED;
b) wrong syntax
c) enum={RED};
d) None
Answer: a)
Purpose of typedef in complex struct declarations:
a) Makes syntax shorter
b) Makes code slower
c) Prevents errors
d) Removes pointers
Answer: a)
offsetof returns:
a) Total struct size
b) Offset of a member
c) Element count
d) Address
Answer: b)
fclose() is used to:
a) Open files
b) Close files
c) Write to files
d) Flush output
Answer: b)
Global variables are:
a) Local
b) Entire program visibility
c) Destroyed early
d) Invalid
Answer: b)
A function call is recognized by:
a) Declaring a function
b) Using its name with parentheses
c) Creating headers
d) Using typedef
Answer: b)

Quick Note **
Intermediate MCQs are common in online assessments, especially for product-based companies where precision matters.
**Bottom Line
These are the MCQs that separate students who “know syntax” from those who understand how C actually behaves.
*Summary *
You now understand headers, memory size, arithmetic evaluations, and dynamic memory basics. These are must-know concepts for clearing written rounds.

Advanced MCQs for Final Placement Rounds

These MCQs involve bitwise operations, memory behavior, function nuances, and low-level execution, the areas interviewers love to test.

volatile indicates:
a) Value never changes
b) Compiler must not optimize it
c) Acts like const
d) Both a and b
Answer: b)
Output?
int i=0; while(i<3) printf("%d ", i++);
a) 0 1 2
b) 1 2
c) Infinite
d) Error
Answer: a)
malloc, calloc, and realloc are all used for:
a) String functions
b) Dynamic memory
c) Math operations
d) File handling
Answer: b)
Evaluate: (5>3 && 3<4)
a) True
b) False
c) Error
d) Undefined
Answer: a)
Left shifting x by 2 bits means:
a) Divide by 2
b) Multiply by 2
c) Multiply by 4
d) Divide by 4
Answer: c)
Bitwise OR of 5 and 3 is:
a) 1
b) 7
c) 8
d) 6
Answer: b)
Output?
int x = 8; printf("%d", x>>1);
a) 8
b) 4
c) 2
d) 16
Answer: b)
Result of 12 & 5:
a) 4
b) 5
c) 0
d) 12
Answer: a)
Which is true about bitwise operators?
a) Work only on floats
b) Work on integer bits
c) Same as logical operators
d) Work on strings
Answer: b)
Output of printf("%d", printf("C"));
a) C1
b) 1C
c) C2
d) CC
Answer: a)
Safest function for reading text with spaces:
a) gets
b) scanf
c) fgets
d) strcpy
Answer: c)
stdarg.h is used for:
a) Arrays
b) File handling
c) Variadic functions
d) Pointers
Answer: c)
feof() checks:
a) Input errors
b) End of file
c) Line numbers
d) Buffer size
Answer: b)
A switch case without break causes:
a) Exit
b) Error
c) Fall-through
d) Restart
Answer: c)
continue in a for-loop:
a) Stops loop
b) Skips to next iteration
c) Ends program
d) None
Answer: b)
Correct nested loop:
a) for(i) for(j)
b) for(i)
c) if(){}
d) while(){}
Answer: a)
restrict keyword tells compiler:
a) Pointer is constant
b) Pointer is only reference to object
c) Pointer is volatile
d) Pointer can't change
Answer: b)
Which keyword prevents compiler optimization?
a) static
b) volatile
c) const
d) inline
Answer: b)
pragma is used for:

a) Defining variables
b) Compiler-specific instructions
c) Memory allocation
d) Type definitions
Answer: b)
Macros are:
a) Variables
b) Functions
c) Preprocessed text replacements
d) Structs
Answer: c)
ifdef compiles code only if:

a) Macro is undefined
b) Macro is defined
c) File is missing
d) Program ends
Answer: b)
Size of struct:
struct T{int a; char b;};
a) 5 bytes
b) 8 bytes
c) 6 bytes
d) 4 bytes
Answer: b)
Size of union:
union D{int a; char b; double c;};
a) sum of all
b) size of double
c) size of char
d) undefined
Answer: b)
Bit-fields are used in embedded systems to:
a) Slow execution
b) Map hardware registers efficiently
c) Replace arrays
d) Remove structs
Answer: b)
Writing to one union member will:
a) Update all members
b) Corrupt other members
c) Keep others intact
d) Expand memory
Answer: b)

Quick Note

Bitwise and volatile-based questions are heavily used in embedded, IoT, and system-level job roles, which are in high demand.

Bottom Line
Advanced MCQs test whether you can think like a systems programmer, precise, logical, and detail-oriented.

Summary
You now know how advanced operators, memory-level instructions, and compiler behaviour influence your C programs, a huge advantage in interviews.

Why These MCQs Matter in 2025

Companies want concept clarity, not memorized syntax.
MCQs expose misunderstandings quickly.
They prepare you for coding rounds, debugging tests, and embedded roles.
Modern interviews heavily rely on online MCQ platforms before allowing coding rounds.
Maste ring these few, high-impact MCQs can dramatically improve your placement performance.

Conclusion

Mastering C MCQs isn’t about memorizing answers; it’s about sharpening the way you think as a programmer. These questions strengthen your fundamentals, expose hidden gaps, and prepare you for real interview logic. With every MCQ you solve, you learn how C behaves internally, not just how it looks in syntax. Consistent practice builds the confidence needed for coding rounds, debugging tests, and system-level interviews. If you stay disciplined and focused, these MCQs will transform you into a clearer, faster, and more industry-ready C programmer.

Why It Matters in 2025
As hiring becomes more competitive, MCQ-based filtering rounds are increasing. Strong MCQ mastery shows technical clarity, something companies value over memorized theory.

Practical Advice

Practice MCQs with explanations, not just answers.
Re-run code fragments to see real behavior.
Build mini projects to strengthen the concepts behind the questions.
Focus on weak areas like pointers, bitwise, and memory management.

FAQs

1. Are C MCQs really used in interviews now?

Yes. Most companies use MCQ-based screening tests before coding rounds because they instantly reveal your concept clarity.

2. How many MCQs should I practice daily?

Even 10–15 well-explained MCQs per day can significantly improve your accuracy and confidence.

3. Do I need to memorize all operators and precedence rules?

No, understanding the logic is far more important. MCQs train you to remember the right patterns.

4. Will these MCQs help for embedded or IoT roles?

Absolutely. Those fields rely heavily on bitwise logic, memory behavior, volatile variables, and pointers.

5. What if I get confused easily during MCQs?

Slow down, revisit the underlying concept, and always read explanations. MCQs make sense only when the concept is clear.

DEV Community