What will be the size of the following structure? struct test { char c; int i; float f; };

The correct answer is D: Depends on padding and alignment. Size depends on compiler's padding and alignment rules. Typically 12 bytes with padding, but varies by system.

What is the purpose of the #ifdef directive?

The correct answer is A: To check if a macro is defined. #ifdef checks if a macro identifier is currently defined. Code following it is compiled only if the macro is defined.

What is the difference between 'const int *p' and 'int * const p'?

The correct answer is C: First prevents changing value, second prevents changing pointer. 'const int *p' - pointer can change but value cannot. 'int * const p' - value can change but pointer cannot.

What is the difference between char str[20] and char *str in C?

The correct answer is B: First is array allocation, second is pointer declaration requiring separate allocation. char str[20] allocates 20 bytes on stack. char *str only declares a pointer and requires separate memory allocation (malloc/static string).

What is the advantage of dynamic allocation over static allocation in competitive programming?

The correct answer is A: Flexibility to use memory based on input size, avoiding stack limits. Dynamic allocation allows using memory proportional to actual input size, preventing TLE from stack overflow with large static arrays and enabling solutions for variable-sized problems.

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C Programming

C language from basics to advanced placement prep

490 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 111–120 of 490

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.111 Medium File Handling

In a program processing a CSV file, what is the most robust approach for reading variable-length lines?

A Use fixed-size buffer with fgets()

B Use getc() in loop and dynamically allocate memory

C Use fscanf() with %s format

D Read entire file into memory at once

Correct Answer: B. Use getc() in loop and dynamically allocate memory

EXPLANATION

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.

Test

Q.112 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.113 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.114 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.115 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.116 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.117 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.118 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.119 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.120 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

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