This pull request adds a corrected version of the "Quick Quiz" program from Chapter 3.

Changes made:

• Created a new file named fix_quiz.c
• Fixed the grading logic based on the correct mark ranges:
  • 90–100 : Grade A
  • 80–89 : Grade B
  • 70–79 : Grade C
  • 60–69 : Grade D
  • 50–59 : Grade E
  • Below 50 : Grade F
• Used scanf to take marks as input from the user
• Added printf to display the calculated grade

This version avoids overlapping or incorrect conditions and ensures accurate output based on the given grading criteria.