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Loops in C#

There may be a situation, when you need to execute a block of code several number of times. In general, the statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.

Programming languages provide various control structures that allow for more complicated execution paths.

A loop statement allows us to execute a statement or a group of statements multiple times and following is the general from of a loop statement in most of the programming languages:

C# provides following types of loop to handle looping requirements. Click the following links to check their detail.

Loop Type	Description
while loop	It repeats a statement or a group of statements while a given condition is true. It tests the condition before executing the loop body.
for loop	It executes a sequence of statements multiple times and abbreviates the code that manages the loop variable.
do...while loop	It is similar to a while statement, except that it tests the condition at the end of the loop body
nested loops	You can use one or more loop inside any another while, for or do..while loop.

While Loop

A while loop statement in C# repeatedly executes a target statement as long as a given condition is true.

Syntax

The syntax of a while loop in C# is:

while(condition)
{
   statement(s);
}

Here, statement(s) may be a single statement or a block of statements. Thecondition may be any expression, and true is any non-zero value. The loop iterates while the condition is true.

When the condition becomes false, program control passes to the line immediately following the loop.

Flow Diagram

Here, key point of the while loop is that the loop might not ever run. When the condition is tested and the result is false, the loop body is skipped and the first statement after the while loop is executed.

Example

using System;
namespace Loops 
{
   class Program
   {
      static void Main(string[] args)
      {
         /* local variable definition */
         int a = 10;

         /* while loop execution */
         while (a < 20)
         {
            Console.WriteLine("value of a: {0}", a);
            a++;
         }
         Console.ReadLine();
      }
   }
} 

When the above code is compiled and executed, it produces the following result:

value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19

For Loop

A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.

Syntax

The syntax of a for loop in C# is:

for ( init; condition; increment )
{
   statement(s);
}

Here is the flow of control in a for loop:

• The init step is executed first, and only once. This step allows you to declare and initialize any loop control variables. You are not required to put a statement here, as long as a semicolon appears.
• Next, the condition is evaluated. If it is true, the body of the loop is executed. If it is false, the body of the loop does not execute and flow of control jumps to the next statement just after the for loop.
• After the body of the for loop executes, the flow of control jumps back up to theincrement statement. This statement allows you to update any loop control variables. This statement can be left blank, as long as a semicolon appears after the condition.
• The condition is now evaluated again. If it is true, the loop executes and the process repeats itself (body of loop, then increment step, and then again testing for a condition). After the condition becomes false, the for loop terminates.

Flow Diagram

Example

using System;
namespace Loops
{
   class Program
   {
      static void Main(string[] args)
      {
         /* for loop execution */
         for (int a = 10; a < 20; a = a + 1)
         {
            Console.WriteLine("value of a: {0}", a);
         }
         Console.ReadLine();
      }
   }
} 

When the above code is compiled and executed, it produces the following result:

value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19

Do...While Loop

Unlike for and while loops, which test the loop condition at the start of the loop, thedo...while loop checks its condition at the end of the loop.

A do...while loop is similar to a while loop, except that a do...while loop is guaranteed to execute at least one time.

Syntax

The syntax of a do...while loop in C# is:

do
{
   statement(s);

}while( condition );

Notice that the conditional expression appears at the end of the loop, so the statement(s) in the loop execute once before the condition is tested.

If the condition is true, the flow of control jumps back up to do, and the statement(s) in the loop execute again. This process repeats until the given condition becomes false.

Flow Diagram

Example

using System;
namespace Loops
{
   class Program
   {
      static void Main(string[] args)
      {
         /* local variable definition */
         int a = 10;
         
         /* do loop execution */
         do
         {
            Console.WriteLine("value of a: {0}", a);
            a = a + 1;
         } 
         while (a < 20);
         Console.ReadLine();
      }
   }
} 

When the above code is compiled and executed, it produces the following result:

value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19

Nested Loops

C# allows to use one loop inside another loop. Following section shows few examples to illustrate the concept.

Syntax

The syntax for a nested for loop statement in C# is as follows:

for ( init; condition; increment )
{
   for ( init; condition; increment )
   {
      statement(s);
   }
   statement(s);
}

The syntax for a nested while loop statement in C# is as follows:

while(condition)
{
   while(condition)
   {
      statement(s);
   }
   statement(s);
}

The syntax for a nested do...while loop statement in C# is as follows:

do
{
   statement(s);
   do
   {
      statement(s);
   }
   while( condition );

}
while( condition );

A final note on loop nesting is that you can put any type of loop inside of any other type of loop. For example a for loop can be inside a while loop or vice versa.

Example

The following program uses a nested for loop to find the prime numbers from 2 to 100:

using System;
namespace Loops
{
   class Program
   {
      static void Main(string[] args)
      {
         /* local variable definition */
         int i, j;
         for (i = 2; i < 100; i++)
         {
            for (j = 2; j <= (i / j); j++)
            if ((i % j) == 0) break; // if factor found, not prime
            if (j > (i / j))
            Console.WriteLine("{0} is prime", i);
         }
         Console.ReadLine();
      }
   }
} 

When the above code is compiled and executed, it produces the following result:

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime

Loop Control Statements

Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.

C# provides the following control statements. Click the following links to check their details.

Control Statement	Description
break statement	Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch.
continue statement	Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating.

Break Statement

The break statement in C# has following two usage:

• When the break statement is encountered inside a loop, the loop is immediately terminated and program control resumes at the next statement following the loop.
• It can be used to terminate a case in the switch statement.

If you are using nested loops (i.e., one loop inside another loop), the break statement will stop the execution of the innermost loop and start executing the next line of code after the block.

Syntax

The syntax for a break statement in C# is as follows:

break;

Flow Diagram

Example

using System;
namespace Loops 
{
   class Program
   {
      static void Main(string[] args)
      {
         /* local variable definition */
         int a = 10;
         
         /* while loop execution */
         while (a < 20)
         {
            Console.WriteLine("value of a: {0}", a);
            a++;
            if (a > 15)
            {
               /* terminate the loop using break statement */
               break;
            }
         }
         Console.ReadLine();
      }
   }
} 

When the above code is compiled and executed, it produces the following result:

value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15

Continue Statement

The continue statement in C# works somewhat like the break statement. Instead of forcing termination, however, continue forces the next iteration of the loop to take place, skipping any code in between.

For the for loop, continue statement causes the conditional test and increment portions of the loop to execute. For the while and do...while loops, continuestatement causes the program control passes to the conditional tests.

Syntax

The syntax for a continue statement in C# is as follows:

continue;

Flow Diagram

Example

using System;
namespace Loops
{
   class Program
   {
      static void Main(string[] args)
      {
         /* local variable definition */
         int a = 10;
         
         /* do loop execution */
         do
         {
            if (a == 15)
            {
               /* skip the iteration */
               a = a + 1;
               continue;
            }
            Console.WriteLine("value of a: {0}", a);
            a++;
         } 
         while (a < 20);
         Console.ReadLine();
      }
   }
} 

When the above code is compiled and executed, it produces the following result:

value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 16
value of a: 17
value of a: 18
value of a: 19

Infinite Loop

A loop becomes infinite loop if a condition never becomes false. The for loop is traditionally used for this purpose. Since none of the three expressions that form the for loop are required, you can make an endless loop by leaving the conditional expression empty.

Example

using System;
namespace Loops
{
   class Program
   {
      static void Main(string[] args)
      {
         for (; ; )
         {
            Console.WriteLine("Hey! I am Trapped");
         }
      }
   }
} 

BMW has the first smart emergency system for motorcycles

While cars and trucks have long had smart emergency systems to send help in the event of a crash (think services like OnStar), motorcycles have had to go without -- a scary thought if you've ever worried about wiping out miles away from help. That's where BMW might just save the day, though. It's introducing the first smart emergency tech for motorbikes, Intelligent Emergency Call, to give the two-wheel crowd a proper safety net. You can trigger it yourself, such as when you need to help a fellow motorist, but the real magic comes with its automatic responses.

IEC's acceleration and lean angle sensors can not only tell if your bike falls or crashes, but time the call for help based on severity. A bad accident will call for help immediately, for instance, while a gentler incident provides a delay so that you can cancel the call. If things are dire enough for that call to go out, it'll send your ride's position at the same time.

Don't expect to see this system in North America, at least not any time soon. IEC will first launch in Germany sometime in early 2017, and it'll spread to other European countries soon afterward. There's no mention of availability in other countries, unfortunately. However, you may well see equipment like this become widespread among bike makers eager to one-up the competition.

World Of Hacking! KALI LINUX

About the Kali Linux Distribution

Kali Linux is an open source project that is maintained and funded by Offensive Security, a provider of world-class information security training and penetration testing services. In addition to Kali Linux, Offensive Security also maintains the Exploit Database and the free online course, Metasploit Unleashed.

Kali Linux Core Developers

Mati Aharoni (muts) is the lead Kali developer, trainer and founder of Offensive Security. With over 10 years of experience as a professional penetration tester, Mati has uncovered several major security flaws and is actively involved in the offensive security arena.

Devon Kearns (dookie) is an Offensive Security instructor, Kali Linux developer, the administrator of the Exploit Database, co-creator of the Metasploit Unleashed project, exploitation fanatic, and co-author of Metasploit: The Penetration Tester’s Guide.

Raphaël Hertzog (buxy) is an experienced Debian developer and consultant, author of the well known Debian Administrator’s Handbook. He’s the packaging wizard in our team and manages our continuously growing development infrastructure.

Kali Linux Developers and Forum Moderators

bolexxx has been administering the Kali forums (and previously BackTrack forums) for over 7 years now, keeping the forums running and spam free. 

steev does our ARM development for Kali Linux. Steev has been working with and on arm devices since 2009 and is also a co-lead of the Gentoo ARM team.

g0tmi1k has been a helping hand and active member since the days of remote-exploit and was promoted to a staff member in 2010.

Sickness is an object of torture and abuse in Offensive Security, and often gets the bad end of our masochistic jokes. He also does kernel exploit stuff.