How Does Arduino Run setup and loop?

• Computer with the Arduino IDE
• Arduino board
• Output signal

What you will learn

• Say what Arduino is and how code is loaded.
• Describe the run order of setup() and loop().
• Explain why loop() has no pause.

Before you start

It helps to know what GPIO is.

What is Arduino?

Arduino is an open-source platform used for building electronics projects. The Arduino IDE uses a simplified version of C++, making it easier to learn to program.

The USB connection is also how you load code onto an Arduino board. The Arduino UNO contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable.

• Sketch
• setup function
• loop function

In what order do setup() and loop() run?

A new sketch in this tutorial is created with the two functions setup() and loop(). The setup() function runs once when the sketch runs, while the loop() function repeats continuously.

After the board is powered up, setup() runs first, followed by loop(). If both are removed and the sketch is left completely blank, it does not pass verification.

• Power up
• setup runs once
• loop runs
• Back to loop

Why does loop() have no pause?

There is no delay automatically built into the loop. When the code in loop() finishes, it starts again immediately.

To slow the loop down, a delay can be added with the delay() function. The first example sketch in the Arduino IDE is Blink.

• Loop without delay
• Loop with delay
• The pause

Real-world example

With an adult, think of a blinking indicator light. The preparation is done once in setup(). Turning the light on and off again and again sits in loop().

Common misunderstandings

setup() repeats along with loop(). setup() runs once, while loop() is the one that repeats continuously.

loop() waits by itself between rounds. No delay is automatically built into the loop; delay() or another timing approach can space operations out.

Frequently asked questions

How do setup() and loop() differ?

setup() runs once when the sketch runs, while loop() repeats continuously.

Can loop() have an empty body?

Yes. The function can be present with no statements inside its braces. Removing both setup() and loop() leaves a blank sketch that does not pass verification.

What is delay() for?

To add a delay and slow the loop down.

How is code loaded onto an Arduino?

Through the USB connection.

Summary

• Arduino is an open-source platform, and a sketch normally includes setup() and loop().
• After power-up, setup() runs once and then loop() repeats continuously.
• loop() has no automatic delay; delay() slows the loop down.