The While loop is simple and is one of the best ways to execute repeated statements. The structure is widely used by R programmers, as well as other programmers. It consists of a constraint condition that follows the “while” keyword. Following the constraint condition, programming statements are written within the loop brackets. Repetitive conditions are performed until the constraint conditions are met.
The while statement is similar to the repeat statement but uses the following syntax.
while (constraint condition) statement1
The while statement, “constraint condition” is evaluated to test if the value is TRUE. When the
“constraint condition” is evaluated, “statement1” is then evaluated. The evaluation process continues until “constraint condition” is evaluated to FALSE. It can be used to repeat a set of instructions when you do not know how the statements will be executed.
The while loop is also similar to the “for” loop, but the iterations are controlled by a conditional statement.
The following is an example of a while loop:
x <- 0 while(x < 6) { x <- x + 1 print(x) }
The following syntax will further explain the while loop as it is used in R:
while (constraint condition)
// while is a keyword; It returns a true or false value
{ //opening curly brackets //Statements within the curly brackets } // closing curly brackets
The output or the results of the constraint condition is a Boolean (true or false) value. This Boolean value is controlled by the code that will enter or quit the loop to execute the statement. If the constraint condition is not met, the code control (program) will go within the loop and execute the statements within the loop. An execution within a while loop is considered an iteration. When the iteration is complete, the code control will return to the beginning and reevaluate the constraint condition within the while loop.
A while loop may have multiple statements that may look like the following syntax:
1. Initialization – Initialization of the constraint variable is the first step in the loop. At this
point the constraint condition is initialized. It is essential that you initialize the constraint variable before you use it in the while loop. If you do not initialize it, the program may crash or the while loop will go into an indefinite loop because it picks up an invalid value from memory.
2. Evaluate Constraint Condition and Statements – The constraint condition within the
while loop is responsible for termination. The program evaluates the value of the constraint condition and if the constraint condition is met, the code control goes into the “while” loop and execute the statements within the code. While loops are iterated until the condition is met.
3. Loop Termination – When the constraint condition is satisfied, the loop is terminated.
The code control will stop executing the while loop.
1. x <- 0 (Initialization) – The statement “x<- 0” shows the initialization of the constraint variable.
2. x < 5 (Evaluate Condition) – The statement “x < 5” shows the constraint condition.
3. x + 1; and print(x) (Evaluate Statements) - The “x + 1” and “print(x)” are the execution statements within the loop.
In the above example, the first iteration evaluates the constraint condition. The constraint condition is not met since x is not initialized to 0. Therefore, the code control will go within the while loop and
execute the statements. When the while loop is iterated the third time, the value of x will be 3. When the final iteration occurs, the while loop will terminate.
Sometimes you may not know where to implement a while loop or how to create the right constraint condition because you may not know what the results will look like. In these circumstances, you can set the constraint conditions to “true”.
The following syntax shows how to set the constraint conditions to “true” within a while loop:
while (true) { statement1;
statement2; }
The while loop with the constraint condition “true” is also used with for loops. This saves helps with loop performance with dynamically allocated vectors.
Constraint conditions are used to break or terminate the while loop, but it is not the only way. You can also use the break and next statements.
The following example shows how to use the break statement within a while loop.
x<-0; while (x < 5) { x <- x + 1; print (x);
if ( x = 4) { break; } }
The above example shows that the “while” loop will terminate when the value of x is 4. The break statement in the while loop terminates before the constraint condition is met.
Sometimes there are errors with the while loop. They often occur within the constraint conditions.
They are semantic and therefore difficult to detect. They may produce false results. To avoid these errors, you must ensure that the constraint variables are performed within the “while” loop because they can lead to indefinite execution.
Although the while loop exhibit errors, it is widely accepted by R programmers as an option to execute infinite conditions in real world scenarios.
When implementing the while loop, you should adhere to following key points:
1. Learn the basic concepts of the while loops and how they are implemented in R
programming. You should start off with learning how the “while” loop works.
2. Ensure that you initialize the constraint condition variable before executing the while
loop. If not, the constraint variable will detect an invalid value from the memory location
and create an infinite while loop.
3. Ensure that you have a constraint variable within the while loop to prevent an indefinite
execution of the while loop.
4. The while loop is the widely accepted method of executing the infinite loops across
various programming languages and in the real world.
5. You can exit the while loop with the constraint condition and break statements.
These key points will help you better understand how the “while” loop work and know how to carefully use it.