Error C2065: 'UBoxComponent': undeclared identifier

I have created a new empty C++ project and then added an AActor class.

On its constructor I have tried to create a UBoxComponent but I get this error:
error C2065: ‘UBoxComponent’: undeclared identifier

This is the header:

// Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "SpawnVolume.generated.h"

UCLASS()
class PLANETARIUMVR_API ASpawnVolume : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	ASpawnVolume();

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;
};

And the class:

// Fill out your copyright notice in the Description page of Project Settings.

#include "SpawnVolume.h"


// Sets default values
ASpawnVolume::ASpawnVolume()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

	UBoxComponent* WhereToSpawn = CreateDefaultSubobject<UBoxComponent>(TEXT("WhereToSpawn"));

	RootComponent = WhereToSpawn;
}

// Called when the game starts or when spawned
void ASpawnVolume::BeginPlay()
{
	Super::BeginPlay();
	
}

// Called every frame
void ASpawnVolume::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

}

I’m very confused because I have another project created with a previous version of Unreal Engine, I have migrated to Unreal 4.16 and I don’t have to include anything to use UBoxComponent.

Do I have to include anything? I think so, but it is very confusing.

You need to include it to use it:

#include "Components/BoxComponent.h"

such as:

 #pragma once
 
 #include "CoreMinimal.h"
 #include "GameFramework/Actor.h"
 #include  "Components/BoxComponent.h"
 #include "SpawnVolume.generated.h"

https://docs.unrealengine.com/latest/INT/Programming/UnrealBuildSystem/IWYUReferenceGuide/

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