Docs: Update 'File Read and Write' and 'Class and Object' Sections for Clarity and Accuracy

[baekilda]

What is this Pull-Request?

This Pull Request addresses specific issues and suggestions in the 'File Read and Write' and 'Class and Object' sections of the documentation.

Changes made

• 498d68f: Update code in read-and-write-files.md to use if-else structure.
• 3bf77ae: Update explanation about the static keyword in classes in class-and-instance.md.

Issue

• Suggestions for Code Correction in 'File Read and Write' and Update on 'Class and Object' Section #40