It is a sample code of "Completed code" on the reference site, but the class name QUICKSTART_API<-this is the code name to show, but adding this will result in a syntax error. If i lose it again, an error will occur. What does this mean? Also, I did copy and paste, but it could not be executed due to a syntax error. I want to know the intention of the official tutorial.

The environment is 4.23.1 of the latest version of Windows 10 Unreal Engine. The editor is Visual studio.
The error message is a syntax error. : Is not a colon;it is

Reference site: https://docs.unrealengine.com/en/Programming/QuickStart/3/index.html

// Copyright 1998-2017 Epic Games, Inc.All Rights Reserved.
#pragma once
#include "GameFramework/Actor.h"
#include "FloatingActor.generated.h"
////// ↓ code.
class QUICKSTART_API AFloatingActor: public AActor
    // Sets default values ​​for this actor's properties
    AFloatingActor ();
    // Called when the game starts or when spawned
    virtual void BeginPlay () override;
    // Called every frame (called every frame)
    virtual void Tick (float DeltaSeconds) override;
float RunningTime;