A struct or a class binds a set of data and the related behavior in a logical unit. This logical unit is like a blueprint for a more abstract data type in our program than those built into the language. So does that mean structs and classes are interchangeable? When would you use a struct instead of a class or vice versa? This article highlights the differences between structures and classes and discusses the use cases of each with examples.
The general rule to follow is that structs should be small, simple (one-level) collections of related properties, that are immutable once created; for anything else, use a class.
C# is nice in that structs and classes have no explicit differences in declaration other than the defining keyword; so, if you feel you need to "upgrade" a struct to a class, or conversely "downgrade" a class to a struct, it's mostly a simple matter of changing the keyword (there are a few other gotchas; structs can't derive from any other class or struct type, and they can't explicitly define a default parameterless constructor).