C# 0 The Complete Reference

PART I

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PART IPART I

public static bool operator false(

param-type operand

)

{

   // return true or false

}

Notice that each returns a 

bool

 result.

The following example shows how 

true

 and 

false

 can be implemented for the 

ThreeD

class. Each assumes that a 

ThreeD

 object is true if at least one coordinate is non-zero. If all 

three coordinates are zero, then the object is false. The decrement operator is also implemented 

for the purpose of illustration.

// Overload true and false for ThreeD.

using System;

// A three-dimensional coordinate class.

class ThreeD {

  int x, y, z; // 3-D coordinates

  public ThreeD() { x = y = z = 0; }

  public ThreeD(int i, int j, int k) { x = i; y = j; z = k; }

  // Overload true.

  public static bool operator true(ThreeD op) {

    if((op.x != 0) || (op.y != 0) || (op.z != 0))

      return true; // at least one coordinate is non-zero

    else

      return false;

  }

  // Overload false.

  public static bool operator false(ThreeD op) {

    if((op.x == 0) && (op.y == 0) && (op.z == 0))

      return true; // all coordinates are zero

    else

      return false;

  }

  // Overload unary --.

  public static ThreeD operator --(ThreeD op)

  {

    ThreeD result = new ThreeD();

    // Return the decremented result.

    result.x = op.x - 1;

    result.y = op.y - 1;

    result.z = op.z - 1;

    return result;

  }

  // Show X, Y, Z coordinates.

  public void Show()

  {

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    Console.WriteLine(x + ", " + y + ", " + z);

  }

}

class TrueFalseDemo {

  static void Main() {

    ThreeD a = new ThreeD(5, 6, 7);

    ThreeD b = new ThreeD(10, 10, 10);

    ThreeD c = new ThreeD(0, 0, 0);

    Console.Write("Here is a: ");

    a.Show();

    Console.Write("Here is b: ");

    b.Show();

    Console.Write("Here is c: ");

    c.Show();

    Console.WriteLine();

    if(a) Console.WriteLine("a is true.");

    else Console.WriteLine("a is false.");

    if(b) Console.WriteLine("b is true.");

    else Console.WriteLine("b is false.");

    if(c) Console.WriteLine("c is true.");

    else Console.WriteLine("c is false.");

    Console.WriteLine();

    Console.WriteLine("Control a loop using a ThreeD object.");

    do {

      b.Show();

      b--;

    } while(b);

  }

}

The output is shown here:

Here is a: 5, 6, 7

Here is b: 10, 10, 10

Here is c: 0, 0, 0

a is true.

b is true.

c is false.

Control a loop using a ThreeD object.

10, 10, 10

9, 9, 9

8, 8, 8

7, 7, 7

6, 6, 6

5, 5, 5

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