Why does Arduino require a void loop() even if it’s empty

Question

Today i had my 10th, or 12th hour of Arduino in University, we were assigned a paper with only 2 parts, the questions and a picture of a TinkerCAD circuit, we had to wire this circuit, then wrote a code to light up the LED TinkerCAD Circuit

i know void setup(){} runs only once, and that void loop(){} loops forever, i wrote the following code to light up the led

 void setup(){
  pinMode(7,OUTPUT);
  digitalWrite(7,HIGH);
}

but Arduino expected a void loop()at the end, even if its empty, why is that?, why cant it run without it since an empty loop is essentially the same as no loop?, what is the reason the compiler cant ignore the lack of a void loop?

Answer 1

What you see in your Arduino sketch is not everything that will be executed in the Arduino board.

Instead they provide you with some friendly functions, so it's easier for makers to easily produce code for the Atmega microcontrollers present in the Arduinos.

You can imagine that there's the following pseudo-program executing in the background of what you see

setup();

while (true) {
    loop();
}

So this program requires you to have a function called setup and a function called loop.

The setup will be called once at the beginning, and the loop will be called again and again in an infinite loop

Leaving loop empty if you don't need it to do anything is perfectly fine, but it's mandatory that you define such function.