Loops

Loops?

  • 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 :

  • While Loop
  • For Loop
  • 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 : 

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.

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();
      }
   }
}

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 : 

for ( init; condition; increment ) {
   statement(s);
}
  • 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 the increment 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.

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();
      }
   }
}

Do...While Loop

Unlike for and while loops, which test the loop condition at the start of the loop, the do...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 : 

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.

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();
      }
   }
}