C questions in placement tests and university exams are rarely about syntax alone. Most of what you will find here is output prediction, pointer arithmetic, arrays and strings, structures and unions, storage classes, recursion, and file handling. The explanations walk through memory behaviour step by step, which is usually where the confusion sits rather than in the code itself.
A program reads struct records using fread(). After reading 100 records of 64 bytes each, what is the total bytes read if successful?
Answer: C
fread(ptr, 64, 100, fp) reads 100 items of 64 bytes each = 6400 bytes total. fread() returns count of items read, not bytes.
Q.42Medium
Which statement correctly counts non-comment lines in a text file?
Answer: C
Pure C solution uses fgets() to read lines and strstr() or manual checking for comment patterns. Option B uses external tool. Option D is inefficient.
Q.43Medium
In a program processing a CSV file, what is the most robust approach for reading variable-length lines?
Answer: B
Dynamic allocation with getc() handles variable-length lines robustly. fgets() with fixed buffer may truncate. fscanf() with %s doesn't handle spaces. Option D wastes memory.
Q.44Medium
A file opened with 'r+b' mode has pointer at position 100. After fwrite(buffer, 1, 50, fp), the pointer is at:
Answer: B
After fwrite() of 50 bytes from position 100, pointer moves to 150. File pointer advances after read/write operations.
Q.45Medium
Which approach correctly implements a file copy function for both text and binary files?
Answer: D
Binary mode works for all files because it's just byte-for-byte copy. Text mode conversions are unnecessary for copying.
Q.46Medium
A program crashes after reading a file. What's most likely the cause if error checking is minimal?
Answer: A
Not checking fopen() return value leads to NULL pointer dereference. Buffer overflow and permissions cause different errors. Disk space affects writing.
Q.47Medium
For a file with 1000 records, which approach minimizes I/O operations?
Answer: B
Single fread() for all records = 1 I/O operation. Loop-based approaches = 1000 operations. Fewer I/O calls = better performance.
Q.48Medium
A program needs to read and write to the same file alternately. Which file mode is most appropriate?
Answer: A
'r+' mode allows both reading and writing without truncating the file. 'w+' truncates the file on opening, 'a+' is for append operations. 'r+' preserves existing content while allowing modifications.
Q.49Medium
What will be the output of fseek(fp, -10, SEEK_END) in a file of 100 bytes?
Answer: A
fseek(fp, -10, SEEK_END) positions the pointer 10 bytes before the end of file. For a 100-byte file, this places it at position 90 (0-indexed). Negative offsets with SEEK_END are valid.
Q.50Medium
In a data structure serialization scenario, what is returned by fwrite() on successful completion?
Answer: A
fwrite(ptr, size, nmemb, fp) returns the number of complete items written, not bytes. If writing 10 items of 4 bytes each but only 35 bytes written, it returns 8, not 35.
Q.51Medium
A competitive exam question requires processing a 500MB CSV file line by line. Which approach is most efficient in terms of memory?
Answer: B
fgets() with a fixed buffer reads one line at a time, maintaining constant memory usage regardless of file size. Option A wastes memory, option D is slowest, and option C may cause issues with large files on some systems.
Q.52Medium
What is the critical issue if ferror(fp) returns non-zero during file operations in a banking application?
Answer: A
ferror() returns non-zero if an error has occurred in file operations. In critical applications like banking, this must be checked to ensure data integrity. This is different from EOF (checked by feof()).
