In C#, What is different between local struct instance and member struct instance? -

it simple c# struct example below.

public struct mystruct {     public int a;      public void foo()     {          //do     } }  public class test {     mystruct st;     void dosomething()     {         st.foo();     }     } 

i had known if use struct instance without new, member field must initialized before use. example above don't have error. why?

this has nothing struct.

in c#, every (local) variable has initialized (assigned value) before can use it.

fields of classes initialized default value when instance of class created, don't have assign value explicitly in constructor.