Sentinel Loops
Explore how to use sentinel values in JavaScript while loops to manage repetition when the number of iterations is unknown. This lesson helps you understand pretest loops, implement input-based loop termination, and practice writing programs like reversing digits, geometric sequences, and finding greatest common divisors.
We'll cover the following...
The sentinel value
Sometimes, the loop doesn’t have a fixed number of repetitions. Instead, an indicator value stops the loop. This special value is called the sentinel value. For example, we don’t know how much data is in a file without reading it all. However, we know that every file ends with an end-of-file (EOF) mark. So, the EOF mark is the sentinel value in this case.
Note: We should select a sentinel value that’s not expected in the normal input.
The while loop
We use the while loop when the termination of the loop depends on the sentinel value instead of a definite number of iterations.
As a simple example, we want to display the reverse sequence of digits in a positive integer value input by the user.
Remember: For some ...