Explain a sketch with comments.

Arduino / C: Use single-line and block comments to document what a sketch does.

/* This sketch sends a startup message.
   Comments are ignored by the compiler. */
void setup() {
  Serial.begin(9600); // Match the Serial Monitor baud rate.
  Serial.println("Sketch ready");
}

void loop() {
  // Nothing repeats in this example.
}

Expected output EXAMPLE

Sketch ready

Details

Targets Arduino Uno R3 (ATmega328P, 16 MHz) with the Arduino AVR core. Open as a sketch in the Arduino IDE and select Arduino Uno. Serial output uses 9600 baud. Tested with simavr; electrical characteristics and physical wiring are outside this simulation. Text after // is a comment until the end of that line. A /* ... */ comment may span several lines. Use comments for intent and wiring notes; executable instructions still need semicolons.

✓ Verified

Tested on Ubuntu 24.04.5 LTS · 2026-11-02 18:28:03 UTC · Uno R3 / ATmega328P at 16 MHz; simavr 1.6+dfsg-3build2 · simavr 1.6+dfsg-3build2; arduino-cli Version: 1.5.1 Commit: 01f3d4f2b Date: 2026-06-05T10:22:17Z; Arduino AVR core 1.8.6

Test inputs, results and environment

The exact published code ran in a dedicated Linux test container with prepared inputs. Snippet process uid 65534 with a read-only root filesystem and temporary working files. Networking disabled. The exact sketch was compiled for Uno R3 and simulated at 16 MHz. UART output is shown below; compiler logs and measured GPIO traces are retained in the test evidence. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.

Architecture / host kernel: x86_64 / 6.18.54.1-microsoft-standard-WSL2
Snippet identity / locale: uid=65534, gid=65534 (unprivileged process) / C.UTF-8
Interpreter invocation: arduino-cli compile --fqbn arduino:avr:uno; uno-sim sketch.ino.elf (capture UART and D13 transitions)
Container image ID: sha256:ec91410a8f6ec3e985830b5e3a0560306d36f8c1c5ccd91a6699abe707123fa3
Code SHA-256: 5c55d631c49698d42e1ace455f095b528d979628a795b38fdfcacd0ec1d7eb7c
Dependencies: simavr 1.6+dfsg-3build2; arduino-cli Version: 1.5.1 Commit: 01f3d4f2b Date: 2026-06-05T10:22:17Z; Arduino AVR core 1.8.6

Test input setup

These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.

Simulator inputs: {"sim_ms": 500, "serial_input": "", "pin_input": "none"}

Observed standard output

Sketch ready

Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.