C# 0 The Complete Reference

PART I

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101

PART IPART I

      while(e > 0) {

        result *= 2;

        e--;

      }

      Console.WriteLine("2 to the " + i + " power is " + result);

    }

  }

}

The output from the program is shown here:

2 to the 0 power is 1

2 to the 1 power is 2

2 to the 2 power is 4

2 to the 3 power is 8

2 to the 4 power is 16

2 to the 5 power is 32

2 to the 6 power is 64

2 to the 7 power is 128

2 to the 8 power is 256

2 to the 9 power is 512

Notice that the 

while

 loop executes only when 

e

 is greater than 0. Thus, when 

e

 is 0, as it is 

in the first iteration of the 

for

 loop, the 

while

 loop is skipped.

The do-while Loop

The third C# loop is the 

do

-

while

. Unlike the 

for

 and the 

while

 loops, in which the condition 

is tested at the top of the loop, the 

do-while

 loop checks its condition at the bottom of the 

loop. This means that a 

do-while

 loop will always execute at least once. The general form of 

the

do-while

 loop is

do {

    

statements

;

} while(

condition

);

Although the braces are not necessary when only one statement is present, they are often 

used to improve readability of the 

do-while

 construct, thus preventing confusion with the 

while

. The 

do-while

 loop executes as long as the conditional expression is true.

The following program uses a 

do

-

while

 loop to display the digits of an integer in 

reverse order:

// Display the digits of an integer in reverse order.

using System;

class DoWhileDemo {

  static void Main() {

    int num;

    int nextdigit;

    num = 198;

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102

 

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

    Console.Write("Number in reverse order: ");

    do {

      nextdigit = num % 10;

      Console.Write(nextdigit);

      num = num / 10;

    } while(num > 0);

    Console.WriteLine();

  }

}

The output is shown here:

Number: 198

Number in reverse order: 891

Here is how the loop works: With each iteration, the leftmost digit is obtained by computing 

the remainder of an integer division by 10. This digit is then displayed. Next, the value in 

num

 is divided by 10. Since this is an integer division, this results in the leftmost digit being 

removed. This process repeats until 

num

 is 0.

The foreach Loop

The

foreach

 loop cycles through the elements of a 

collection.

 A collection is a group of objects. 

C# defines several types of collections, of which one is an array. The 

foreach

 loop is examined 

in Chapter 7, when arrays are discussed.

Using break to Exit a Loop

It is possible to force an immediate exit from a loop, bypassing any code remaining in the 

body of the loop and the loop’s conditional test, by using the 

break

 statement. When a 

break

 statement is encountered inside a loop, the loop is terminated, and program control 

resumes at the next statement following the loop. Here is a simple example:

// Using break to exit a loop.

using System;

class BreakDemo {

  static void Main() {

    // Use break to exit this loop.

    for(int i=-10; i <= 10; i++) {

      if(i > 0) break; // terminate loop when i is positive

      Console.Write(i + " ");

    }

    Console.WriteLine("Done");

  }

}

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