-- Operator (C# Reference)
The decrement operator (--) decrements its operand by 1. The decrement operator can appear before or after its operand: --variable and variable--. The first form is a prefix decrement operation. The result of the operation is the value of the operand "after" it has been decremented. The second form is a postfix decrement operation. The result of the operation is the value of the operand "before" it has been decremented.
Numeric and enumeration types have predefined decrement operators.
User-defined types can overload the -- operator (see operator). Operations on integral types are generally allowed on enumeration.