IT1907
03 Handout 2 *Pr operty of STI
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Looping
Loops
A loop ref ers to a construct that enable s a program to exe cute a block of stateme nts or a loop body repetitively as long as the
define d condition evaluates to true. Looping i s used whe n an operation needs to repeat multi ple ti mes. The C# pr ovides three
(3) looping structures:
• while – This loop repeats a block of statements as l ong as a given condition evaluates to true. It evaluates the condition
first before executing the loop body.
• do…while – This is similar with while l oop, exce pt that it exe cutes the bl ock of statements be fore eval uating the given
condition regardless if it evaluates to true or false.
• for – This loop repeats a block of statement for a specified number of times.
The while Loop
The while loop repeats a block of statements as long as a given condition is true. The fol lowing is the ge neral syntax of while
loop in C# including an example :
Syntax:
while (condition) {
//statements in loop body
}
For example:
//this will print a sequence of numbers from 1 to 10
int start = 1;
while (start <= 10) {
Console.WriteLine(start);
start++;
}
The conditio n can be a relational or logical expression that must return a true or false value. When the given condition in th e
while loop evaluates to true, the l oop body will execute and the conditi on is reevaluated. If the condition evaluates to true
again, the loop body will continue to execute until the given condition evaluates to false and the execution jumps to the
statements after the while loop.
In the given example, the initialized variable start is a loop control variable that is used to control the loop condition. The
while loop will print the numbers from 1 to 10. It is i mportant to include statements within the loop that will update the loop
condition to false to termi nate the loop exe cution. Otherwi se , the loop body continues to exe cute endlessly. This is called
infinite loop. In the example, the statement start++; is used to update the condition on the while loop.
The do-while Loop
The do…while loop executes the loop body first before evaluating the given loop conditi on. The following is the general syntax
of do…while loop in C# including the example:
Syntax:
do {
//statements in loop body
} while (condition);
For example:
//this will print a sequence of numbers from 1 to 10
int start = 1;
do {
Console.WriteLine(start);
start++;
} while (start <= 10);
The do statement exe cutes the loop body first, then evaluates the given condition in the while statement. If the condition
eval uates to false, the loop terminates. If it eval uates to true, then the loop body is executed again. This process repeats
until the given condition evaluates to false.
In the given e xample, the do statement ex ecutes the loop body fi rst then evaluates the given condition in the while statement.
Similar with while loop, it is important to include statements withi n the loop body that will update the loop condition to false
to terminate the loop execution.
