How to use "GetComponent" and "transform" code in dll file?

When i try to use "GetComponent" and "transform" codes in my **dll** file but it shows some error like "This name GetComponent and transform does not exist in current context". I use using UnityEngine also but it's still the same error. Here is my code 1. Bounds bounds = GetComponent().mesh.bounds; 2. Vector4 v3Center = transform.GetComponent().center;