Count five LED flashes with a for loop.
Arduino / C: Repeat an LED action a known number of times and print the current count.
void setup() {
Serial.begin(9600);
pinMode(LED_BUILTIN, OUTPUT);
for (byte count = 1; count <= 5; count++) {
Serial.println(count);
digitalWrite(LED_BUILTIN, HIGH);
delay(20);
digitalWrite(LED_BUILTIN, LOW);
delay(20);
}
}
void loop() {
}Expected output EXAMPLE
1 2 3 4 5
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. The for statement starts count at one, checks the limit before each pass, and increments it afterward. Increase both delays for a more visible sequence. The five flashes happen once after upload or Reset.
Tested on Ubuntu 24.04.5 LTS · · 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
cab5d2db008d2a176cd3d4ba5fee033395540a4ab835a3252f17d1a00ebb7523- 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
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Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.
Additional assertions that passed
Checks recorded by the test harness. Where Python assertions are shown, browser cases use Playwright and simulator cases may inspect pin transitions: result.stdout is captured output, work is the temporary directory, and Path is pathlib.Path. The harness also imports json and csv.
trace = [tuple(map(int, line.split(','))) for line in Path('pin13.csv').read_text().splitlines()]
pulses = [(trace[i+1][0] - cycle) / 16000 for i, (cycle, value) in enumerate(trace[:-1]) if value == 1 and trace[i+1][1] == 0]
assert len(pulses) == 5 and all(18 <= width <= 22 for width in pulses) and trace[-1][1] == 0