In C, what happens when a function is called before its declaration?

The correct answer is B: Compilation error occurs. C requires function declaration before use (forward declaration or definition). Calling without prior declaration causes compilation error in modern C standards.

What is the output of: printf("%d", (int)3.7);?

The correct answer is B: 3. Type casting (int)3.7 truncates the decimal part, converting 3.7 to 3. The fractional part is discarded.

Which of the following correctly uses #pragma once for header file protection in 2024 standards?

The correct answer is B: #pragma once is widely supported by modern compilers and is preferred over include guards. While #pragma once is technically non-standard, it is supported by virtually all modern compilers (GCC, Clang, MSVC) since 2024. It's simpler than include guards and prevents multiple inclusion more elegantly. Both approaches work, but #pragma once is increasingly preferred.

What is the primary purpose of function pointers in C?

The correct answer is B: To provide polymorphism and dynamic function dispatch. Function pointers enable polymorphism by allowing runtime selection of which function to call. They are crucial for implementing callbacks and dynamic function dispatch.

In a for loop for(int i = 0; i < 5; i++), at what point does the increment happen?

The correct answer is B: After executing the loop body. For loop order: initialization → check condition → execute body → increment → repeat from condition check.

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C Programming
File Handling

C language from basics to advanced placement prep

52 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 52

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.11 Medium File Handling

Which statement correctly counts non-comment lines in a text file?

A Read each line and skip if first non-whitespace char is '//'

B Use grep to filter comments before processing

C Read line with fgets(), check for '//' pattern, increment counter if not found

D Use fscanf() with format specifier to skip comment lines

Correct Answer: C. Read line with fgets(), check for '//' pattern, increment counter if not found

EXPLANATION

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.

Test

Q.12 Medium File Handling

A program reads struct records using fread(). After reading 100 records of 64 bytes each, what is the total bytes read if successful?

A 100

B 64

C 6400

D fread() doesn't return bytes, only count

Correct Answer: C. 6400

EXPLANATION

fread(ptr, 64, 100, fp) reads 100 items of 64 bytes each = 6400 bytes total. fread() returns count of items read, not bytes.

Test

Q.13 Medium File Handling

What happens if you call fclose() on an already closed file pointer?

A Returns 0

B Returns EOF and may cause undefined behavior

C Silently succeeds

D Raises compile-time error

Correct Answer: B. Returns EOF and may cause undefined behavior

EXPLANATION

Calling fclose() on closed file causes undefined behavior and returns EOF. This is a runtime issue, not compile-time.

Test

Q.14 Medium File Handling

A program needs to append 500 integers to an existing binary file. Which combination is correct?

A fopen(file, 'ab') with fwrite()

B fopen(file, 'a') with fprintf()

C fopen(file, 'ab') with fprintf()

D fopen(file, 'wb') with fwrite()

Correct Answer: A. fopen(file, 'ab') with fwrite()

EXPLANATION

Binary append requires 'ab' mode with fwrite(). Option B uses text mode. Option D would overwrite. Option C mixes binary mode with text function.

Test

Q.15 Medium File Handling

A C program must securely close a file and handle potential errors. What is the best approach?

A if(fclose(fp) != 0) { handle_error(); }

B fclose(fp); assuming it always succeeds

C Just let the OS close file when program exits

D Use multiple fclose() calls for safety

Correct Answer: A. if(fclose(fp) != 0) { handle_error(); }

EXPLANATION

fclose() returns 0 on success and EOF (-1) on error. Checking return value ensures buffered data is flushed and handles errors like write failures.

Test

Q.16 Medium File Handling

In competitive exam file handling questions, if fseek() is called with SEEK_CUR, what does it indicate?

A Seek relative to current file pointer position

B Seek from the beginning of file

C Seek from the end of file

D Seek to current directory location

Correct Answer: A. Seek relative to current file pointer position

EXPLANATION

SEEK_CUR is a constant meaning 'current position'. fseek(fp, offset, SEEK_CUR) moves the pointer by 'offset' bytes from its current position.

Test

Q.17 Medium File Handling

A program reads structured data: fread(ptr, sizeof(struct), count, fp). If fread() returns a value less than 'count', what could be the reason?

A End of file reached before reading all items

B File pointer is NULL

C sizeof(struct) is too large

D The file was opened in text mode instead of binary

Correct Answer: A. End of file reached before reading all items

EXPLANATION

fread() returns the number of items actually read. If less than 'count' is returned, it indicates EOF was reached or a read error occurred before completing the request.

Test

Q.18 Medium File Handling

In a file opened with 'rb+' mode, what operations can be performed?

A Reading and writing binary data without truncating

B Only reading binary data

C Only writing binary data

D Reading, writing, and truncating

Correct Answer: A. Reading and writing binary data without truncating

EXPLANATION

'rb+' opens a binary file for both reading and writing. The file must exist. Existing content is preserved and can be overwritten at any position.

Test

Q.19 Medium File Handling

What is the difference between 'rb' and 'r' modes when opening a file?

A 'rb' opens in binary mode, 'r' opens in text mode with newline conversion

B 'rb' allows reading, 'r' allows both reading and writing

C Both are identical in modern C compilers

D 'r' is faster than 'rb' for large files

Correct Answer: A. 'rb' opens in binary mode, 'r' opens in text mode with newline conversion

EXPLANATION

'rb' (binary read) reads data as-is without converting line endings. 'r' (text read) converts platform-specific newlines (\r\n on Windows) to \n.

Test

Q.20 Medium File Handling

A program needs to update specific bytes in the middle of a file without affecting other data. Which approach is most suitable?

A Use fseek() to position pointer, then fwrite() the new data

B Read entire file, modify in memory, write back

C Use file append mode to add changes

D Create new file with corrected data

Correct Answer: A. Use fseek() to position pointer, then fwrite() the new data

EXPLANATION

Using fseek() with r+ or w+ mode allows direct access to specific file positions. This is efficient for small modifications without rewriting the entire file.

Test

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