updated the parentheses_checker.cpp

[Dhaval-0511]

Issues found and fixed in parentheses_checker.cpp by me :
this issue is #8760

1. Use of non-standard header <bits/stdc++.h>:

   • Issue: <bits/stdc++.h> is a GCC-specific header that includes all standard libraries.
     This reduces portability and increases compile time unnecessarily.
   • Fix: Replaced with specific standard headers: , , and .

2. Single line input only:

   • Issue: The code reads only one line from input and then exits, which limits usage in batch testing.
   • Fix: Changed to a loop reading multiple lines until EOF to allow processing multiple input lines.

3. Lack of descriptive comments for functions and code blocks:

   • Issue: Code lacks sufficient inline comments, which may confuse future readers or collaborators.
   • Fix: Added clear, concise comments explaining each function’s purpose and key logic points.

4. Vague input prompt message:

   • Issue: The prompt only requests a single line and doesn't clarify how to end input.
   • Fix: Updated the prompt to instruct users on how to input multiple lines and how to terminate input.

5. Unused commented code with vector tests:

   • Issue: Unnecessary commented-out vector tests in main(), cluttering the code.
   • Fix: Removed or suggested to move to separate unit tests to keep main() clean and focused.

6. Minor formatting and style inconsistencies:

   • Issue: Inconsistent indentation and style affect readability.
   • Fix: Reformatted code consistently following common C++ style conventions.

7. Ignored other characters in string without comment:

• Issue: The treatment of non-parenthesis characters was implicit and not clearly noted.
  • Fix: Added a brief comment to clarify that non-bracket characters are ignored.

These fixes improve code clarity, portability, usability for multiple inputs, maintainability, and user experience.