Do while loop repetition control structure - Java tutorial for beginners

do while loop repetition control structure - Java tutorial for beginners

In this video, we are going to talk about the third type of repetition control structure which is the do while loop

Here is a typical example of how a do while loop statement looks like

int score = 0;

do {
System.out.print(score + “ “);
score++;
}
while (score less than 10);

Let me now explain the various elements in this statement
First, do, here is a reserved word in Java and it is telling us that this particular statement is a do while loop
After the keyword, do, we get the action statements
These action statements can be a simple statement, having just one statement like this
Or, it can be a compound statement which is made up of more than one action statement
Always make sure to surround with curly braces in case of compound action statement

Next, there is another reserved word while
Then, the following expression is called the loop condition

You can notice that in this loop statement the action statement comes before the condition

That means that during the execution, the action statement executes first
And then the loop condition is evaluated right after.

If the loop condition evaluates to true, then the action statement will execute again
As long as the loop condition evaluates to true, then the action statement will continue to execute
So, in order to avoid an infinite loop, you have to make sure that the body of the loop contains a statement that would make the loop condition evaluate to false at a certain point of the execution

That’s the reason why we put the statement score++
See, if we remove that statement score++ from the code
And run, there we are going to get an infinite loop

Let me put the statement score++ back
And run
There, we have the result in the console

The do while loop is somehow different from the while loop or the for loop
In the while and for loops, the loop condition is evaluated first before the action statement
So, these loops might never activate at all
Especially, in the cases where the condition evaluates to false right from the entry point of the loop

Consider this while loop

int score = 10;
while (score less than 10)
{
System.out.print(score + " ");
score++;
}
System.out.println();

Run this while loop and notice that it produces nothing
This is because, the entry condition evaluates to false right at the beginning
So, the while loop will not activate at all
You either need to adjust the condition or the value stored in the variable score

Meanwhile, in the do while loop, the condition is evaluated after the action statement
That means that the body of the loop always executes at least once
Even if the condition is false at the beginning of the execution


Consider this do while loop
int score = 10;
do
{
System.out.print(score + " ");
score++;
}
while (score less than 10);
System.out.println();

Run this portion of code
Notice that it returns the number 10 and it also increments the value of score to 11

So guys, that’s it about do while looping structure

Thanks for watching and I hope it was informative.
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Let’s meet in the next video.

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