Write a program that reads a numeric grade and prints a letter grade. Use these ranges: 90-100 is A, 80-89 is B, 70-79 is C, 60-69 is D, below 60 is F. You'll practice chaining else if statements in the right order.
I'll show you why checking 90 first, then 80, then 70 works, but reversing the order breaks the logic. Test with scores like 95, 85, 75, 65, and 55. Your program should print exactly one letter for each input.
Handle invalid input like negative numbers or scores over 100.