Can't Add Objects to a TArray

i’m a Unreal Engine beginner, i’m not able to add objects to my TArray.

UPROPERTY(BlueprintReadWrite, Category = "Code")
		TArray<UTrash*> Trashes;

When a call TArray::Add nothing happends and TArray::Num is still 0.

UE_LOG(LogTemp, Warning, TEXT("Elements: %f"),Trashes.Num());     //It always writes 0!

UTrash is a my custom class, should the problem be in UTrash?
Thanks for the help.

Trashes.Num() returns an int value but %f logs a float. If you want to log an int value use %d.

For other values see: