Detailed explanation and use of swift guard keyword

func buy( money: Int , price: Int , capacity: Int , volume: Int){

  if money >= price{
    if capacity >= volume{
      print("I can buy it!")
      print("\(money-price) Yuan left.")
      print("\(capacity-volume) cubic meters left")
    }
    else{
      print("No enough capacity")
    }
  }
  else{
    print("Not enough money")
  }
}

func buy2( money: Int , price: Int , capacity: Int , volume: Int){

  guard money >= price else{
    print("Not enough money")
    return
  }

  guard capacity >= volume else{
    print("Not enough capacity")
    return
  }

  print("\(money-price) Yuan left.")
  print("\(capacity-volume) cubic meters left")
}