Read a single character grade and print a category, using a switch statement – not an if/else if chain.
Both the uppercase and lowercase form of a letter should count: 'A' and 'a' both mean Excellent, 'B' and
'b' both mean Good, and everything else means Needs work.
This is exactly the “stack case labels with no code between them” trick from the lesson, applied on purpose: two
labels, one shared block, one break at the end of each group.