Csharp/CSharp Tutorial/Operator/Prefix Postfix Operator

Increment and Decrement

The ++ and the -- are the increment and decrement operators.

The increment operator adds 1 to its operand, and the decrement operator subtracts 1.

<source lang="csharp">x = x + 1;</source>

Operators ++

<source lang="csharp">using System;

 class Class1
 {
   [STAThread]
   static void Main(string[] args)
   {
     MyCar car = 5;
           for( int i = 0; i < 20; ++i )
           {
               car++;
               Console.WriteLine( "{0}", car.GetSpeed());
           }
   }
 }
 public class MyCar
 {
       private static int speed = 2;
       private const int maxSpeed = 200;
       
       public bool ChangeSpeed(int newSpeed)
       {
           if( newSpeed > maxSpeed )
               return false;
           speed = newSpeed;
           return true;
       }
       public static MyCar operator ++( MyCar car )
       {
           car.ChangeSpeed(++speed);
           return car;
       }
       public static implicit operator MyCar( int from )
       {
           MyCar car = new MyCar();
           car.ChangeSpeed( from );
           return car;
       }
       public int GetSpeed()
       {
           return speed;
       }
 }</source>

postfix decrement

<source lang="csharp">class MainClass {

 public static void Main()
 {
   int length = 3;
   int newLength = length--;
   System.Console.WriteLine("Postfix decrement example");
   System.Console.WriteLine("length = " + length);
   System.Console.WriteLine("newLength = " + newLength);
 }

}</source>

Postfix decrement example
length = 2
newLength = 3

postfix increment

<source lang="csharp">class MainClass {

 public static void Main()
 {
   int length = 3;
   int newLength = length++;
   System.Console.WriteLine("Postfix increment example");
   System.Console.WriteLine("length = " + length);
   System.Console.WriteLine("newLength = " + newLength);
 }

}</source>

Postfix increment example
length = 4
newLength = 3

Pre And Post Increment

<source lang="csharp">using System; class MainClass {

  static void Main()
  {
     int x = 5, y;
     y = x++;                        
     Console.WriteLine("y: {0}, x: {1}", y, x);
     x = 5;
     y = ++x;                        
     Console.WriteLine("y: {0}, x: {1}", y, x);
     x = 5;
     y = x--;                        
     Console.WriteLine("y: {0}, x: {1}", y, x);
     x = 5;
     y = --x;                        
     Console.WriteLine("y: {0}, x: {1}", y, x);
  }

}</source>

y: 5, x: 6
y: 6, x: 6
y: 5, x: 4
y: 4, x: 4

prefix decrement

<source lang="csharp">class MainClass {

 public static void Main()
 {
   
   int length = 3;
   int newLength = --length;
   System.Console.WriteLine("Prefix decrement example");
   System.Console.WriteLine("length = " + length);
   System.Console.WriteLine("newLength = " + newLength);
 }

}</source>

Prefix decrement example
length = 2
newLength = 2

prefix increment

<source lang="csharp">class MainClass {

 public static void Main()
 {
   int length = 3;
   int newLength = ++length;
   System.Console.WriteLine("Prefix increment example");
   System.Console.WriteLine("length = " + length);
   System.Console.WriteLine("newLength = " + newLength);
 }

}</source>

Prefix increment example
length = 4
newLength = 4

The difference between prefix and postfix forms of ++

<source lang="csharp">using System;

class Example {

 public static void Main() {    
   int x, y; 
   int i; 

   x = 1; 
   Console.WriteLine("Series generated using y = x + x++;"); 
   for(i = 0; i < 10; i++) { 
     y = x + x++; // postfix ++ 
     Console.WriteLine(y + " "); 
   } 
   Console.WriteLine(); 

   x = 1; 
   Console.WriteLine("Series generated using y = x + ++x;"); 
   for(i = 0; i < 10; i++) { 
     y = x + ++x; // prefix ++ 
     Console.WriteLine(y + " "); 
   } 
   Console.WriteLine(); 
   
 } 

}</source>

Series generated using y = x + x++;
2
4
6
8
10
12
14
16
18
20
Series generated using y = x + ++x;
3
5
7
9
11
13
15
17
19
21

Using the Post-Increment Operator

<source lang="csharp">class MainClass {

 static void Main()
 {
   int count;
   int result;
   count = 0;
   result = count++; 
   System.Console.WriteLine("result = {0} and count = {1}",result, count);
 }

}</source>

Using the Pre-Increment Operator

<source lang="csharp">class MainClass {

 static void Main()
 {
   int count;
   int result;
   count = 0;
   result = ++count;
   System.Console.WriteLine("result = {0} and count = {1}", result, count);
 }

}</source>