C Programming — MCQ Practice Questions & Answers

Question 1

Write a code snippet to read 100 bytes from a file. Which is correct?

Accepted Answer

Correct answer: A. fread(buffer, 1, 100, fp); — fread() syntax is fread(ptr, size, count, stream). To read 100 bytes, size=1 and count=100. Option B reads 100 items of 1 byte each, which is equivalent but less clear.

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B. fread(buffer, 100, 1, fp);

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C. fread(buffer, 100, fp);

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D. fread(100, buffer, fp);

Question 2

Which of the following correctly implements appending to a file?

Accepted Answer

Correct answer: A. FILE *fp = fopen("file.txt", "a"); — Mode "a" opens a file for appending. New data is written at the end of the file. Mode "w" truncates the file, "r+" requires file to exist, "ab+" is appending in binary with both read/write.

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B. FILE *fp = fopen("file.txt", "w");

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C. FILE *fp = fopen("file.txt", "r+");

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D. FILE *fp = fopen("file.txt", "ab+");

Question 3

In a program reading a binary file of 1000 integers, fread() is called as: fread(arr, sizeof(int), 1000, fp). If only 500 integers are present, what will fread() return?

Accepted Answer

Correct answer: A. 500 — fread() returns the number of complete items successfully read, not the number of bytes. It will return 500 even if 1000 were requested.

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B. An error code

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C. NULL

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D. The bytes read (typically 2000)

Question 4

Consider using fseek() on a file opened in text mode with SEEK_END and a non-zero offset. What is the standard behavior?

Accepted Answer

Correct answer: B. It is undefined behavior and may not work correctly on all platforms — In text mode, fseek() with non-zero offset relative to SEEK_END is undefined behavior. Use fseek(fp, 0, SEEK_END) for reliable behavior.

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A. It is guaranteed to work correctly on all platforms

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C. It always returns an error

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D. It works only on Windows systems

Question 5

A program writes data using fprintf() and later attempts to read it back. However, the read operation fails intermittently. What could be the most likely cause?

Accepted Answer

Correct answer: B. The buffer was not flushed before reading, causing incomplete data — fprintf() buffers output. Without flushing (fflush() or fclose()), subsequent read operations may see incomplete data. This is a common source of bugs.

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A. fprintf() is not suitable for output operations

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C. The file was opened in binary mode instead of text mode

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D. The file pointer was not reset after writing

Question 6

What is the purpose of using fflush() in file handling, and when is it critical to use it?

Accepted Answer

Correct answer: B. To write buffered data to the actual file on disk — fflush() writes any buffered data to the underlying file. It's critical when you need to ensure data is written to disk before continuing, especially before reading the same file.

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A. To move file pointer to the beginning of the file

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C. To close the file gracefully

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D. To clear error flags from the stream

Question 7

A program writes binary data using fwrite() but reads it back with fprintf(). What will happen?

Accepted Answer

Correct answer: B. Binary data will be misinterpreted; text formatting won't apply — Mixing write (fwrite - binary) and read (fprintf - formatted text) functions on same data causes mismatch. Binary data won't have format specifiers; misinterpretation results.

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A. Data will be read correctly

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C. Program will crash

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D. Only null bytes will be read

Question 8

A program uses fgetc() to read 100,000 characters from a file sequentially. Which alternative would be more efficient?

Accepted Answer

Correct answer: B. Use fread() with appropriate buffer size — fread() with buffer reads multiple bytes per call, reducing function call overhead. fgetc() makes 100,000 separate calls. fgets() is limited to reading up to newline.

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A. Use fgets() with larger buffer

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C. Use fscanf() with %c format

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D. Continue with fgetc(); efficiency doesn't matter

C Programming - MCQ Practice Questions