I can't use some codes in dll file?

I try to create an dll file and i have to use the following codes in it
1.float Val= PlayerPrefs.GetFloat (“value”);
2.Time.deltaTime
3.Input.GetMouseButtonDown.
it gives an error “The name “PlayerPrefs” does not exist in current context”.
I am new for unity.

The script stubs created by Unity’s editor have “using UnityEngine;” added to their top. But in your dll, the namespace “UnityEngine” is not automatically included. So it doesn’t know what PlayerPrefs is, because that’s a static class which is a member of the UnityEngine namespace.

Add “using UnityEngine;” to the top of those of your classes that use it in the DLL.