Foundations

Execution Trace

Follow the program counter, the current statement, and how each step changes state.

Variables & Mutation

Assignment, overwriting, and references — watch old values give way to new ones.

Arrays & Indexing

Contiguous storage, indices, traversal, and what going out of bounds really means.

Loops & Invariants

Loop variables, the invariant that holds each pass, and the termination condition.

Recursion & the Call Stack

Calls pushed and popped, return values, and a recursion unwinding frame by frame.

Big-O by Counting Steps

Build O(1), O(n), O(n²), and O(log n) intuition by counting operations on screen.

State Machines

States, events, and transitions — the groundwork for TCP, OS, and parsers.