What is the correct way to allocate and initialize a structure dynamically? struct Node { int data; int next; };

The correct answer is D: Both A and B are equally correct. Both A and B allocate memory correctly; B includes explicit typecasting which is optional in C but good practice.

What will be printed? #define DEBUG 1 #if DEBUG printf("Debug mode ON"); #else printf("Debug mode OFF"); #endif

The correct answer is A: Debug mode ON. Since DEBUG is defined as 1 (non-zero), the #if DEBUG condition is true, so only the code in #if block executes. The #else block is skipped.

Which storage class has a default value of 0 if not explicitly initialized?

The correct answer is C: static. Static variables are initialized to 0 by default. auto and register variables have garbage values if not initialized. extern variables are declared elsewhere.

What does the third parameter of fseek() represent?

The correct answer is B: The reference point (origin) for seeking. Third parameter is 'whence': SEEK_SET (beginning), SEEK_CUR (current position), SEEK_END (end). Second parameter specifies offset in bytes.

What will be the output of this recursive function? int fact(int n) { if(n

The correct answer is C: 120. This calculates factorial. fact(5) = 5*4*3*2*1 = 120. Base case n

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C Programming

C language from basics to advanced placement prep

197 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–50 of 197

Topics in C Programming

All Basics & Syntax 86 Data Types & Variables 97 Control Flow 100 Functions 99 Arrays & Strings 100 Pointers 99 Structures & Unions 100 File Handling 100 Dynamic Memory 98 Preprocessor 99

Q.41 Hard Dynamic Memory

Which statement about dynamic memory is TRUE?

A Dynamic memory is faster than stack memory

B Dynamic memory persists until explicitly freed

C Dynamic memory is limited by cache size

D Dynamic memory is automatically freed at function end

Correct Answer: B. Dynamic memory persists until explicitly freed

EXPLANATION

Dynamic memory persists until free() is called, unlike automatic variables which are freed at function end.

Test

Q.42 Hard Dynamic Memory

What will happen if malloc() fails and returns NULL but code doesn't check?

A Program automatically allocates from stack

B Dereferencing NULL causes undefined behavior/crash

C Memory is automatically reallocated

D Exception is raised

Correct Answer: B. Dereferencing NULL causes undefined behavior/crash

EXPLANATION

Dereferencing a NULL pointer causes undefined behavior, typically resulting in segmentation fault or program crash.

Test

Q.43 Hard File Handling

In a program that processes binary files with variable-length records, what could cause fread() to return fewer items than requested without reaching EOF?

A A read error occurred during I/O operation

B The file is opened in text mode instead of binary mode

C The buffer size is larger than remaining file size

D All of the above

Correct Answer: D. All of the above

EXPLANATION

fread() can return fewer items due to: (A) I/O errors, (B) text mode conversions affecting byte count, or (C) insufficient data remaining. For robust code, check ferror() and feof() after fread() returns less than requested.

Test

Q.44 Hard File Handling

For implementing a file locking mechanism in a competitive exam environment, which approach correctly handles concurrent file access in POSIX systems?

A Using flock() or fcntl() system calls with F_WRLCK

B Opening file in 'a' mode ensures automatic locking

C Using fseek() to check if file is accessible

D Creating a separate lock file and checking its existence

Correct Answer: A. Using flock() or fcntl() system calls with F_WRLCK

EXPLANATION

flock() and fcntl() with F_WRLCK provide kernel-level file locking in POSIX systems. Option B is false, option C doesn't provide locking, and option D is unreliable due to race conditions.

Test

Q.45 Hard File Handling

A program reads serialized objects using fread(). What's the primary risk when file format changes between versions?

A fread() will fail silently

B Buffer overflow or misaligned struct interpretation

C File size becomes invalid

D Automatic version detection prevents issues

Correct Answer: B. Buffer overflow or misaligned struct interpretation

EXPLANATION

Changed file format causes struct misalignment, leading to buffer overflow or garbage data. No automatic detection in C. Need version headers or checksums.

Test

Q.46 Hard File Handling

When implementing a log file writer with concurrent access, what's the critical issue with standard fopen()?

A fopen() is too slow

B No built-in file locking mechanism

C fopen() doesn't support append atomically

D Memory leaks after multiple opens

Correct Answer: B. No built-in file locking mechanism

EXPLANATION

Standard C fopen/fwrite lack file locking. Multiple processes can corrupt data. Need OS-specific locking (flock/fcntl on Unix) or use 'a' mode with small writes.

Test

Q.47 Hard File Handling

For competitive exam file validation: A 2GB file must be processed without loading entirely in memory. Which strategy is optimal?

A Read entire file into heap-allocated buffer

B Use mmap() for memory-mapped I/O

C Read in fixed-size chunks in loop

D Use external sorting tools

Correct Answer: C. Read in fixed-size chunks in loop

EXPLANATION

Fixed-size chunk processing is standard for large files. mmap() helps but may not be portable. Loading entire file exhausts memory. External tools bypass C programming.

Test

Q.48 Hard File Handling

A program processes encrypted binary data with fread(). Why might using 'r' mode instead of 'rb' cause corruption?

A Text mode converts line endings, corrupting binary data

B Text mode stops at null bytes

C Text mode is slower

D Text mode reduces buffer size

Correct Answer: A. Text mode converts line endings, corrupting binary data

EXPLANATION

Text mode on Windows converts CRLF to LF and vice versa, corrupting binary. Binary mode preserves exact bytes. Null byte handling is secondary concern.

Test

Q.49 Hard File Handling

What does rewind(fp) accomplish compared to fseek(fp, 0, SEEK_SET)?

A rewind() is faster

B rewind() also clears error indicators; fseek() doesn't

C They are functionally identical

D fseek() works only in binary mode

Correct Answer: B. rewind() also clears error indicators; fseek() doesn't

EXPLANATION

rewind(fp) resets pointer AND clears EOF/error flags. fseek(fp, 0, SEEK_SET) only repositions. rewind is essentially: fseek(...); clearerr(...);

Test

Q.50 Hard File Handling

For reading a configuration file line-by-line where lines may exceed 256 characters, which function is recommended for ISRO/GATE 2024 exams?

A fgets(buffer, sizeof(buffer), fp) with dynamic memory if needed

B fscanf(fp, "%s", buffer) with fixed-size array

C fgetc() in a loop to manually read lines

D fread() to read entire file at once

Correct Answer: A. fgets(buffer, sizeof(buffer), fp) with dynamic memory if needed

EXPLANATION

fgets() is safest for line reading with size protection. For lines exceeding buffer size, use dynamic allocation or getline(). fscanf() with %s is vulnerable to buffer overflow.

Test

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