Question

How can I store (save) a variable, so that i can use it after I close and run the program again? I can’t use saveFileDialog cause it is 2D array. Other programs have their own extension. Can I make my own extension, too? Something like “Save project as…”.

Answer 1

If you want to save some object to the disk, you either need to devise some file format for your data, or use one of the existing, generic ones.

In .Net, probably the simplest way is to use the binary formatter to do this:

void Save(SomeType obj, string fileName)
{
    using (var stream = File.OpenWrite(fileName))
    {
        var formatter = new BinaryFormatter();
        formatter.Serialize(stream, obj);
    }
}

The obj object and all objects it references have to be serializable. Most primitive types already are serializable and you can make your own types serializable by using the [Serializable] attribute.

The Load() method would be similar, except it would use File.OpenRead() and formatter.Deserialize().

How to choose the file name is up to you, but you certainly can use SaveFileDialog for that.