Update stack.c

[Imran-imtiaz48]

Improvements Made:

1. Renamed Functions:Changed isfull to isFull and isempty to isEmpty to follow standard camelCase naming conventions.
2. Error Messages: Added newlines (\n) in error messages for better formatting.
3. Print Logic: Updated printStack to iterate from 0 to s->top (inclusive) instead of using count. This avoids relying on a global variable.
4. Memory Management: Added free(s) at the end of the main function to release allocated memory.
5. Comments: Added detailed comments to explain the purpose of each function and critical lines of code.
6. Variable Names: Used more descriptive names (e.g., Stack instead of st, newItem instead of newitem) for better clarity.