Beginner Java Exercise: Sentinel Values and Do-While Loops

In my previous post on while loops, we used a loop-continuation-condition to test the arguments. In this example, we'll loop at a sentinel-controlled loop. The sentinel value is a special input value that tests the condition within the while loop.

To jump right to it, we'll test if an int variable is not equal to 0.

The data != 0 within the while (data != 0) { ... } is the sentinel-controlled-condition.

In the following example, we'll keep adding an integer to itself until the user enters 0. Once the user enters 0, the loop will break and the user will be displayed with the sum of all of the integers that he/she has entered.



As you can see from the code above, the code is somewhat redundant. It asks the user to enter an integer twice: Once before the loop begins, and an x amount of times within the loop (until the user enters 0).

A better approach would be through a do-while loop. In a do-while loop, you "do" something "while" the condition is true. Since the "do" is placed ahead of the while conditional testing scenario, PHP will execute that code first. So the first time PHP reads the code, it'll execute the "do" statement and then test the while scenario. This ensures that the code is executed at least once before any condition is tested.