-- 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.

Remarks

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.

Example

// cs_operator_decrement.cs
using System;
class MainClass
{
    static void Main() 
    {
        double x;
        x = 1.5;
        Console.WriteLine(--x);
        x = 1.5;
        Console.WriteLine(x--);
        Console.WriteLine(x);
    }
}

Output

0.5
1.5
0.5

See Also

Reference

C# Operators

Concepts

C# Programming Guide

Other Resources

C# Reference