C file modes: Given FILE *fp; fp = fopen('NOTES.TXT', 'r+'); which operations on the file are permitted by the mode 'r+' (read/update without truncation)?

Introduction / Context:
In C standard I/O, the two-character (or three-character) mode string passed to fopen controls not only whether a file is opened for reading or writing, but also whether it is treated as text or binary, whether content is preserved or truncated, and whether writes append at end. Understanding the exact meaning of each mode prevents accidental data loss and enables the correct combination of reading and writing behaviors for update-style workflows.

Given Data / Assumptions:

• Code uses: FILE *fp; fp = fopen('NOTES.TXT', 'r+');
• We assume the file exists and can be opened.
• Platform is a standard-conforming C environment; text vs. binary is not explicitly specified (no 'b').

Concept / Approach:

• Mode 'r' means open an existing file for reading; the file must already exist.
• Adding '+' upgrades the stream to update mode: both input and output are permitted on the same stream.
• Without an 'a' (append) or 'w' (write-truncate) component, the file is neither truncated nor forced to append-only. You may read and write anywhere (subject to fseek/fflush rules between direction changes).

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• Reading: Incomplete; 'r+' also allows writing.
• Writing: Incomplete; 'r+' also allows reading.
• Appending: That is characteristic of 'a'/'a+' modes, not 'r+'.
• None of the above: Incorrect because 'Read and Write' precisely describes 'r+'.

Common Pitfalls:

• Forgetting to call fflush or fseek between a read then write (or vice versa) on the same update stream; the C standard requires a positioning or flush operation when switching direction.
• Assuming 'r+' creates the file if missing; it does not—use 'w+' or 'a+' when creation is needed.

Final Answer: