In C#, an operator is a program element that is applied to one or more operands in an expression or statement. Operators that take one operand, such as the increment operator (++) or new, are referred to as unary operators. Operators that take two operands, such as arithmetic operators (+,-,*,/), are referred to as binary operators. One operator, the conditional operator (?:), takes three operands and is the sole ternary operator in C#.
This sixth iteration of the C# language is provided by the Roslyn compiler. This compiler came out with version 4.6 of the .NET Framework, however it can generate code in a backward compatible manner to allow targeting earlier framework versions. C# version 6 code can be compiled in a fully backwards compatible manner to .NET 4.0. It can also be used for earlier frameworks, however some features that require additional framework support may not function correctly.
Constructors are methods in a class that are invoked when an instance of that class is created. Their main responsibility is to leave the new object in a useful and consistent state.
Destructors/Finalizers are methods in a class that are invoked when an instance of that is destroyed. In C# they are rarely explicitely written/used.