Do-While Loop in C#

Unlike for and while loops, which test the loop condition at the top of the loop, the do...while loop checks its condition at the bottom 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 do_while

{
 

class Program
  

{
     

static void Main(string[] args)
      

{
 

 int table,i,res;
       

 table=12;
       

 i=1;
       

 do
         

{
          

 res = table * i;
         

 Console.WriteLine("{0} x {1} = {2}", table, i, res);
          

 i++;
         

}
 // must put semi-colon(;) at the end of while               condition in do...while loop.
       

 while (i <= 10);
 
       

 Console.ReadLine();
      

}
  

 }

}

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

12 x 1 = 12
12 x 2 = 24
12 x 3 = 36
12 x 4 = 48
12 x 5 = 60
12 x 6 = 72
12 x 7 = 84
12 x 8 = 92
12 x 9 = 108
12 x 10 = 120 

For Loop in C#

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:

1. 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.
2. 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.
3. After the body of the for loop executes, the flow of control jumps back up to the incrementstatement. 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.
4. 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 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

While Loop in C#

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. The condition 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 will be skipped and the first statement after the while loop will be 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

Loop in C#

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A loop statement allows us to execute a statement or group of statements multiple times and following is the general from of a loop statement in most of the programming languages:
For brief knowledge about different types of loop click on the link given in table.

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

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

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 (click here)	Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch.
continue statement (click here)	Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating.

The 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.

using System;

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

When the conditional expression is absent, it is assumed to be true. You may have an initialization and increment expression, but programmers more commonly use the for(;;) construct to signify an infinite loop.

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