Nested switch Statements

Þ   Nested switch Statements

→   It is possible to have a switch as part of the statement sequence of an outer switch. This is called a nested switch.

*      2.2.2 Looping structure

1.    The For Loop

→   You can repeatedly execute a sequence of code by creating a loop. C# supplies a powerful assortment of loop constructs. The one we will look at here is the for loop.

→   For repeating a block, the general form is

for(initialization; condition; iteration)

{

statement sequence

   }

→   The initialization is usually an assignment statement that sets the initial value of the loop control variable, which acts as the counter that controls the loop.

→   The condition is a Boolean expression that determines whether the loop will repeat. The iteration expression defines the amount by which the loop control variable will change each time the loop is repeated.

→   Notice that these three major sections of the loop must be separated by semicolons. The for loop will continue to execute as long as the condition tests true.

→   Once the condition becomes false, the loop will exit, and program execution will resume on the statement following the for.

→   An important point about for loops is that the conditional expression is always tested at the top of the loop. This means that the code inside the loop may not be executed at all if the condition is false to begin with.

2.    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. As with the for loop, the while checks the conditional expression at the top of the loop.

3.    The do-while Loop

→   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.

4.    The foreach Loop

→   The foreach loop is used to cycle 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 general form of foreach is shown here:

foreach(type loopvar in collection) statement;

→   Here, type loopvar specifies the type and name of an iteration variable. The iteration variable receives the value of the next element in the collection each time the foreach loop iterates.

→   When the loop begins, the first element in the array is obtained and assigned to loopvar. Each subsequent iteration obtains the next element from the array and stores it in loopvar. The loop ends when there are no more elements to obtain. Thus, the foreach cycles through the array one element at a time, from start to finish.

→   One important point to remember about foreach is that the iteration variable loopvar is read-only. This means you can’t change the contents of an array by assigning the iteration variable a new value.