Q:

How to create a common function for all forms using c#?

I need to call a single function from all forms. In vb.net there is an option module. In this module we can create functions/variables and we call them from anywhere in the project. Is there any option in C# like this module? 
Finally, if I need to use a single function in my entire project, is this possible or not? 

A:

Are you looking for a static class?
 namespace MyNamespace {
   ...
   public static class MyStaticClass {
     public static int MyFunc(int x) {
       return x * 2;
     } 
   }
   ...
 }

And you can call it 
 using MyNamespace;

 ...

 int result = MyStaticClass.MyFunc(123);

you may want to add static import in order to get rid of MyStaticClass:
 using static MyNamespace.MyStaticClass;

 ...

 // Just "MyFunc", no need to the class name being mentioned 
 int result = MyFunc(123);

