15-minute session: read for 3 minutes, trace for 3, experiment for 7, and complete the check for 2. Spend longer whenever you need.
A program is a set of instructions. Read the example from its entry point to the output statement. Text in quotes is data; the output operation is an instruction. Predict the printed line before running. Change only the message, run again, then remove one required punctuation mark and read the first error. Restore the working source.
let introduces an immutable binding and var a mutable one. Converting text with Int(raw) may produce nil. if let unwraps a present value without force-unwrapping missing data.
print("Ready")
Expected result: Ready
Keep three notes: your prediction, the actual result, and why they match or differ. The completion check grades understanding; the practice task builds skill.