How can I reference a C# class from a different file?

Question

I'm new to programming, and am trying to learn C# using a Mono compiler for BBEdit's "TextWrangler" program (something like NotePad++, but for Mac). My question, however, is pretty straightforward: I am trying to code a very simple program in C# that uses a class from a different .cs file.

And I am struggling with it. If the classes were in the same .cs file, I have no issues; otherwise, the bash terminal keeps giving me errors. Here's my code:

Program.cs:

//  Client class, where Main method calls the Car method

using System;
using Auto;

namespace Auto
{    
    class Program
    {        
        public static void Main(string[] args)
        {        
            //Instantiate car class
            Car car = new Car("Toyota", "Corolla", "Sedan", 2014, 25000);
            Console.WriteLine(car.Maintenance());
            Console.Read();
        }
    }
}

Car.cs:

//  "Car" class (does NOT include the Main method)

using System;

namespace Auto
{
    public class Car
    {
        //Create various attributes for Car Class with getters and setters
        public string Make { get; set; }
        public int Year { get; set; }
        public string Model { get; set; }
        public string Type { get; set; }
        public int Millage { get; set; }
        public DateTime PurchaseDate { get; set; }

        //Constructor to instantiate Car object that pass all the necessary attribute values 
        public Car(string make, string model, string _type, int year, int millage)
        {
            Make = make;
            Model = model;
            Type = _type;
            Millage = millage;
        }

        //Maintenance method will check all the inspection that the mechanic has to do     based on the millage of the car
        public string Maintenance()
        {
            int index = 1;
            string maintenanceList = string.Empty;
            if (Millage > 5000)
                maintenanceList += (index++).ToString() + ". Oil Change " +Environment.NewLine;     
            if (Millage > 10000)
            {
                maintenanceList += (index++).ToString() + ". Check Brakes " +     Environment.NewLine;
                maintenanceList += (index++).ToString() + ". Rotate Tires " + Environment.NewLine;
                maintenanceList += (index++).ToString() + ". Lube Hinges, Lock, and Latches" + Environment.NewLine;
            }

            if (Millage > 15000)
                maintenanceList += (index++).ToString() + ". Replace air Cleaner element" + Environment.NewLine;

            if (Millage > 30000)
                maintenanceList += (index++).ToString() + ". Replace Dust and Pollen Filter" + Environment.NewLine;

            return maintenanceList;
        }
    }
}

So there you go. The code's simpler than it seems- but whenever I try to compile these files, both saved under the same folder in my Finder, I get these results:

Program.cs:

Compilation failed: 1 error(s), 0 warnings

Program.cs(14,13): error CS0246: The type or namespace name `Car' could not be found.      Are you missing an assembly reference?
Program.cs(15,31): error CS0841: A local variable `car' cannot be used before it is declared

Car.cs:

error CS5001: Program `Car.exe' does not contain a static `Main' method suitable for an entry point

So yeah, I'm stuck. I've poured over many sources on introductory class building in C#, but my luck has yielded nothing. Any help would be very much appreciated.

Answer 1

Your errors in the "Program.cs" file are not relevant here. They will disappear as soon as you've fixed the one in the "Car.cs" file.

1. there is an error in "Car.cs"
2. it does not compile
3. there is no DLL generated
4. it cannot be found when compiling the "Program.cs" file

Fix one, the other will be fixed too.

The question remains: how to fix the error in "Car.cs". This is certainly a problem in the file attributes in your project file.

Some possible answers can be found here be most certainly here when pixaloop wrote:

Change the Output Type under the Project > Properties to that of a “Class Library”. By default, this setting may have been set to a “Console Application”.

As a side note, you should try MonoDevelop for your C# development in MacOS. It will ease your project/files/dll management.