[c#] How to use class from other files in C# with visual studio?

I am a newbie of C# and MS visual studio, and I want to use the C# class which defined in another file, but can't get it work.

Here is the program.cs(and why can't I rename that file ?)

using System;

namespace TestCSharp2
{
    class Program
    {
        static void Main(string[] args)
        {
            Class2 class2 = new Class2();
            // here the IDE will complain that cant find namespace or balabala..
            class2.setValue(10);
            Console.WriteLine(class2.getValue().ToString());
            Console.ReadKey();
        }
    }
}

And here is the Class2 that I want to use in file Class2.cs:

namespace TestCSharp2
{
    class Class2
    {
        int i;
        public void setValue(int i)
        {
            this.i = i;
        }
        public int getValue()
        {
            return this.i;
        }
    }
}

Should I #include or something? isn't use namespace enough?

As some guys asked if they are in the same assembly/same project, I presume they were, because here is the procedure how they are created:

• A new project using the template of Console C# Project, then the program.cs was created by default.
• The Class2.cs was created with [File] -> [New] -> [File] -> [C# class] and saved in the same folder where program.cs lives.

To be honest, I don't know if they are in same assembly / same project, but I guess they were.

Yeah, I just made the same 'noob' error and found this thread. I had in fact added the class to the solution and not to the project. So it looked like this:

Just adding this in the hope to be of help to someone.

It would be more beneficial for us if we could see the actual project structure, as the classes alone do not say that much.

Assuming that both .cs files are in the same project (if they are in different projects inside the same solution, you'd have to add a reference to the project containing Class2.cs), you can click on the Class2 occurrence in your code that is underlined in red and press CTRL + . (period) or click on the blue bar that should be there. The first option appearing will then add the appropriate using statement automatically. If there is no such menu, it may indicate that there is something wrong with the project structure or a reference missing.

You could try making Class2 public, but it sounds like this can't be a problem here, since by default what you did is internal class Class2 and thus Class2 should be accessible if both are living in the same project/assembly. If you are referencing a different assembly or project wherein Class2 is contained, you have to make it public in order to access it, as internal classes can't be accessed from outside their assembly.

As for renaming: You can click Program.cs in the Solution Explorer and press F2 to rename it. It will then open up a dialog window asking you if the class Program itself and all references thereof should be renamed as well, which is usually what you want. Or you could just rename the class Program in the declaration and again open up the menu with the small blue bar (or, again, CTRL+.) and do the same, but it won't automatically rename the actual file accordingly.

Edit after your question edit: I have never used this option you used, but from quick checking I think that it's really not inside the same project then. Do the following when adding new classes to a project: In the Solution Explorer, right click the project you created and select [Add] -> [Class] or [Add] -> [New Item...] and then select 'Class'. This will automatically make the new class part of the project and thus the assembly (the assembly is basically the 'end product' after building the project). For me, there is also the shortcut Alt+Shift+C working to create a new class.

namespace TestCSharp2
{
    **public** class Class2
    {
        int i;
        public void setValue(int i)
        {
            this.i = i;
        }
        public int getValue()
        {
        return this.i;
        }
    }
}

Add the 'Public' declaration before 'class Class2'.

I was having the same problem here. Found out that the problem was with an Advanced Property of the file. There is there an option with the name 'Compilation Action' (may be not with the exact words, I am translating - my VS is in Portuguese).

My Class1.cs file was there as "Content" and I just had to change it to "Compile" to make it work, and have the classes recognized by the others files in the same project.

According to your example here it seems that they both reside in the same namespace, i conclude that they are both part of the same project ( if you haven't created another project with the same namespace) and all class by default are defined as internal to the project they are defined in, if haven't declared otherwise, therefore i guess the problem is that your file is not included in your project. You can include it by right clicking the file in the solution explorer window => Include in project, if you cannot see the file inside the project files in the solution explorer then click the show the upper menu button of the solution explorer called show all files ( just hove your mouse cursor over the button there and you'll see the names of the buttons)

Just for basic knowledge: If the file resides in a different project\ assembly then it has to be defined, otherwise it has to be define at least as internal or public. in case your class is inheriting from that class that it can be protected as well.