Sentinel-controlled while loop - Java tutorial with PRACTICAL example

Sentinel-controlled while loop - Java tutorial with a PRACTICAL example

Hi and welcome back to this channel
Today we are going to have a look at another form that a while loop may take in a program.
Previously we talked about counter-controlled loops
In this video particularly we will talk about another form of while loops which is called the Sentinel-controlled while loop
This while loop form is often used when you do not know exactly how many times a set of statements needs to be executed
But instead, you do know that the statements need to be executed until a special value is met.
This special value is called a sentinel

The portion of code on the screen is a typical example of a Sentinel-controlled while loop

int sentinel = 100;
int score =0;

while (score != sentinel) {
score = score + 20;
}

In this example, we have started by declaring and initializing the Sentinel variable, here sentinel
Next, we have initialized the loop control variable score as well

In the while statement, we are using the loop condition to test the loop control variable score against the Sentinel variable sentinel

As long as, the loop control variable is different from the sentinel then the action statement will execute
The first action statement will output the values of the variable score
And the second action statement will increment the value of the variable score by 20, whenever the loop condition is met

Let’s take another example
Suppose we want to create a program that will read integer values and sum them up.
But we do not know exactly how many numbers the user needs to type in.
So, in our program, we are going to determine an integer value that will be considered a Sentinel and that value will be used to mark the end of the input data.

In this program, I want the user to input data from the keyboard
So, I will create an input object

Next, I will declare and initialize the Sentinel variable
I prefer it to be a static variable
static final int SENTINEL = 10;

public static void main(String[] args)
{

Next, I need to declare the various variables that will be used in this program
The first variable will be used to store the input numbers by the user
int number;
The second variable will hold the sum of all the numbers inputted by the user
int sum = 0;

The third variable will be the loop control variable
int counter = 0;

Next, we will write an output statement that will prompt the user to input the integer number

Let’s write the input statement

After, we will write the while loop statement
The loop condition will test the variable number against the variable Sentinel
while (number != SENTINEL)
{
If the condition is met
Here are the action statements to execute
The first will be an input statement that will allow the user to input the numbers

The second statement will operate the sum of the numbers entered by the user
sum = sum + number;

The third statement will be used to increment the variable counter
counter++;
}

Out of the while loop
I need to write the output statement

We can also add an if statement
That will allow us to print a message in case there is no input in the program

if (counter != 0) {
}
else {
}

So, once everything is set up correctly
You can now run your program

That’s it about the Sentinel-controlled while loop, in the next video I will talk about the flag-controlled while loop

Thanks for viewing, I hope this video was informative.
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Let’s meet in the next video.

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