C# 0 The Complete Reference

i

 is not accessible outside the 

for

 loop. If you need to use the loop control 

variable elsewhere in your program, you will not be able to declare it inside the 

for

 loop.

Before moving on, you might want to experiment with your own variations on the 

for

loop. As you will find, it is a fascinating loop.

The while Loop

Another of C#’s loops is the 

while

. The general form of the

 while

 loop is

while(

condition

)

statement

;

where 

statement

 can be a single statement or a block of statements, and 

condition

 defines the 

condition that controls the loop and may be any valid Boolean expression. The statement is 

performed while the condition is true. When the condition becomes false, program control 

passes to the line immediately following the loop.

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Here is a simple example in which a 

while

 is used to compute the order of magnitude of 

an integer:

// Compute the order of magnitude of an integer

using System;

class WhileDemo {

  static void Main() {

    int num;

    int mag;

    num = 435679;

    mag = 0;

    Console.WriteLine("Number: " + num);

    while(num > 0) {

      mag++;

      num = num / 10;

    };

    Console.WriteLine("Magnitude: " + mag);

  }

}

The output is shown here:

Number: 435679

Magnitude: 6

The

while

 loop works like this: The value of 

num

 is tested. If 

num

 is greater than 0, the 

mag

counter is incremented, and 

num

 is divided by 10. As long as the value in 

num

 is greater 

than 0, the loop repeats. When 

num

 is 0, the loop terminates and 

mag

 contains the order of 

magnitude of the original value.

As with the 

for

 loop, the 

while

 checks the conditional expression at the top of the loop, 

which means that the loop code may not execute at all. This eliminates the need for performing 

a separate test before the loop. The following program illustrates this characteristic of the 

while

loop. It computes the integer powers of 2 from 0 to 9.

// Compute integer powers of 2.

using System;

class Power {

  static void Main() {

    int e;

    int result;

    for(int i=0; i < 10; i++) {

      result = 1;

      e = i;

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