Lectures

We formalize the “rules” of the “Guess the Number” game as a model: what counts as an attempt, when the game ends, and how to handle invalid input. We separate settings and state using val/ var, introduce invariants and early checks via require(...), express rules as functions ( validateGameSettings, isInRange), and agree on where exactly attempt ++ lives. At the end, we outline the scenario skeleton and review typical mistakes.

We break down how to fairly generate a secret number in Kotlin using kotlin.random.Random: the Random.nextInt( from, until) contract, why the upper bound is excluded, where the “off-by-one” error comes from, and how to avoid it with the max + 1 formula. We write the generateSecret() function, add require for fail-fast, do a quick boundary check, and discuss nuances: nextInt(range) and seed for reproducible debugging.

We break down how to turn a “wall of code” in main() into a set of clear functions: move input into readGuessOrNull() with result type Int ?, isolate pure logic in compareGuess(), assemble human-readable hints via hintText(), and formulate contracts (“input/output/side effects/error”) so that null and toIntOrNull() work for you, not against you.

We break down the “heartbeat” of a Kotlin guessing game: how to build an attempts loop using while with an attempt counter, why the condition attempt <= maxAttempts reads more honestly, how to integrate robust input via readGuessOrNull and Int ?, where continue and break fit, and how to avoid off-by-one bugs caused by putting attempt ++ in the wrong place. At the end — a single main () and an execution-flow diagram.

We break down how to turn “kinda works” into reproducible behavior: we build scenarios (input, boundaries, win/lose), lock down randomness via debug mode, add targeted println logs, catch “off-by-one” issues around attempt ++ and <= conditions, verify branching via when, add safety checks with require/ check, and use the basic debugger in IntelliJ IDEA (breakpoints, stepping, value inspection).