可以重新定義或重載大部分C#提供內置的運算符。因此，程序員可以使用使用用戶定義類型運算符也是如此。重載運算符符合特殊名稱關鍵字操作之後的操作符號被定義的功能。像其他功能，重載運算符返回類型和參數列表。

例如，看一下下麵的函數：

public static Box operator+ (Box b, Box c)
{
   Box box = new Box();
   box.length = b.length + c.length;
   box.breadth = b.breadth + c.breadth;
   box.height = b.height + c.height;
   return box;
}

上述功能實現了加法運算符(+)，用於一個用戶定義的類Box。它增加了兩個Box對象的屬性，並返回得到Box對象。

運算符重載的實現

下麵的程序顯示了完整的實現：

using System;

namespace OperatorOvlApplication
{
   class Box
   {
      private double length;      // Length of a box
      private double breadth;     // Breadth of a box
      private double height;      // Height of a box

      public double getVolume()
      {
         return length * breadth * height;
      }
      public void setLength( double len )
      {
         length = len;
      }

      public void setBreadth( double bre )
      {
         breadth = bre;
      }

      public void setHeight( double hei )
      {
         height = hei;
      }
      // Overload + operator to add two Box objects.
      public static Box operator+ (Box b, Box c)
      {
         Box box = new Box();
         box.length = b.length + c.length;
         box.breadth = b.breadth + c.breadth;
         box.height = b.height + c.height;
         return box;
      }

   }

   class Tester
   {
      static void Main(string[] args)
      {
         Box Box1 = new Box();         // Declare Box1 of type Box
         Box Box2 = new Box();         // Declare Box2 of type Box
         Box Box3 = new Box();         // Declare Box3 of type Box
         double volume = 0.0;          // Store the volume of a box here

         // box 1 specification
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);

         // box 2 specification
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);

         // volume of box 1
         volume = Box1.getVolume();
         Console.WriteLine("Volume of Box1 : {0}", volume);

         // volume of box 2
         volume = Box2.getVolume();
         Console.WriteLine("Volume of Box2 : {0}", volume);

         // Add two object as follows:
         Box3 = Box1 + Box2;

         // volume of box 3
         volume = Box3.getVolume();
         Console.WriteLine("Volume of Box3 : {0}", volume);
         Console.ReadKey();
      }
   }
}

讓我們編譯和運行上麵的程序，這將產生以下結果：

Volume of Box1 : 210
Volume of Box2 : 1560
Volume of Box3 : 5400

重載與非重載操作符

下表描述了運算符在C#重載的能力：

運算符	描述
+, -, !, ~, ++, --	這些一元運算符需要一個操作數，並可以被重載
+, -, *, /, %	這些二元運算符需要一個操作數，並可以被重載
==, !=, <, >, <=, >=	比較操作符可以被重載
&&, ||	條件邏輯運算符不能直接重載
+=, -=, *=, /=, %=	賦值運算符不能被重載
=, ., ?:, ->, new, is, sizeof, typeof	這些運算符不能被重載

例子：

在上麵討論中，讓我們擴展前麵的例子，並重載幾個運算符：

using System;

namespace OperatorOvlApplication
{
    class Box
    {
       private double length;      // Length of a box
       private double breadth;     // Breadth of a box
       private double height;      // Height of a box
      
       public double getVolume()
       {
         return length * breadth * height;
       }
      public void setLength( double len )
      {
          length = len;
      }

      public void setBreadth( double bre )
      {
          breadth = bre;
      }

      public void setHeight( double hei )
      {
          height = hei;
      }
      // Overload + operator to add two Box objects.
      public static Box operator+ (Box b, Box c)
      {
          Box box = new Box();
          box.length = b.length + c.length;
          box.breadth = b.breadth + c.breadth;
          box.height = b.height + c.height;
          return box;
      }
      
      public static bool operator == (Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length == rhs.length && lhs.height == rhs.height 
             && lhs.breadth == rhs.breadth)
          {
              status = true;
          }
          return status;
      }
      public static bool operator !=(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length != rhs.length || lhs.height != rhs.height 
              || lhs.breadth != rhs.breadth)
          {
              status = true;
          }
          return status;
      }
      public static bool operator <(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length < rhs.length && lhs.height 
              < rhs.height && lhs.breadth < rhs.breadth)
          {
              status = true;
          }
          return status;
      }

      public static bool operator >(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length > rhs.length && lhs.height 
              > rhs.height && lhs.breadth > rhs.breadth)
          {
              status = true;
          }
          return status;
      }

      public static bool operator <=(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length <= rhs.length && lhs.height 
              <= rhs.height && lhs.breadth <= rhs.breadth)
          {
              status = true;
          }
          return status;
      }

      public static bool operator >=(Box lhs, Box rhs)
      {
          bool status = false;
          if (lhs.length >= rhs.length && lhs.height 
             >= rhs.height && lhs.breadth >= rhs.breadth)
          {
              status = true;
          }
          return status;
      }
      public override string ToString()
      {
          return String.Format("({0}, {1}, {2})", length, breadth, height);
      }
   
   }
    
   class Tester
   {
      static void Main(string[] args)
      {
        Box Box1 = new Box();          // Declare Box1 of type Box
        Box Box2 = new Box();          // Declare Box2 of type Box
        Box Box3 = new Box();          // Declare Box3 of type Box
        Box Box4 = new Box();
        double volume = 0.0;   // Store the volume of a box here

        // box 1 specification
        Box1.setLength(6.0);
        Box1.setBreadth(7.0);
        Box1.setHeight(5.0);

        // box 2 specification
        Box2.setLength(12.0);
        Box2.setBreadth(13.0);
        Box2.setHeight(10.0);

       //displaying the Boxes using the overloaded ToString():
        Console.WriteLine("Box 1: {0}", Box1.ToString());
        Console.WriteLine("Box 2: {0}", Box2.ToString());
        
        // volume of box 1
        volume = Box1.getVolume();
        Console.WriteLine("Volume of Box1 : {0}", volume);

        // volume of box 2
        volume = Box2.getVolume();
        Console.WriteLine("Volume of Box2 : {0}", volume);

        // Add two object as follows:
        Box3 = Box1 + Box2;
        Console.WriteLine("Box 3: {0}", Box3.ToString());
        // volume of box 3
        volume = Box3.getVolume();
        Console.WriteLine("Volume of Box3 : {0}", volume);

        //comparing the boxes
        if (Box1 > Box2)
          Console.WriteLine("Box1 is greater than Box2");
        else
          Console.WriteLine("Box1 is  greater than Box2");
        if (Box1 < Box2)
          Console.WriteLine("Box1 is less than Box2");
        else
          Console.WriteLine("Box1 is not less than Box2");
        if (Box1 >= Box2)
          Console.WriteLine("Box1 is greater or equal to Box2");
        else
          Console.WriteLine("Box1 is not greater or equal to Box2");
        if (Box1 <= Box2)
          Console.WriteLine("Box1 is less or equal to Box2");
        else
          Console.WriteLine("Box1 is not less or equal to Box2");
        if (Box1 != Box2)
          Console.WriteLine("Box1 is not equal to Box2");
        else
          Console.WriteLine("Box1 is not greater or equal to Box2");
        Box4 = Box3;
        if (Box3 == Box4)
          Console.WriteLine("Box3 is equal to Box4");
        else
          Console.WriteLine("Box3 is not equal to Box4");

        Console.ReadKey();
      }
    }
}

讓我們編譯和運行上麵的程序，這將產生以下結果：

Box 1: (6, 7, 5)
Box 2: (12, 13, 10)
Volume of Box1 : 210
Volume of Box2 : 1560
Box 3: (18, 20, 15)
Volume of Box3 : 5400
Box1 is not greater than Box2
Box1 is less than Box2
Box1 is not greater or equal to Box2
Box1 is less or equal to Box2
Box1 is not equal to Box2
Box3 is equal to Box4