Difference between revisions of "Java/C2/while-loop/English"

Welcome

Learning Outcomes

About the while loop.

How To use it.

Tools Used

Ubuntu 11.10,

JDK 1.6 and

Eclipse 3.7

Prerequisites

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While loop

It has two parts.

One is the loop running condition and the second is the loop variable.

Let us now look at an example. Switch to Eclipse

Minimize Slides and open Eclipse

Eclipse should contain the following code.

public class WhileDemo{

public static void main(String[] args){

}

}

I have created a class WhileDemo and added the main method to it.

int n = 1;

Type int n = 1

int n = 1;

while (n <= 10)

while (n <= 10)

It means the loop will run as long as this condition is true.

In our case, it will run as long as the value of n is less than or equal to 10.

And it will stop only when the value of n become greater than 10.

while (n <= 10) {

System.out.println(n);

n = n + 1;

}

 System.out.println(n); and then increment

n = n + 1;

Then increment statement

Highlight print statement

Then increment statement.

Since it is true.

2 is printed and   n becomes 3.

So Let us see the code in action.

As we can see, the numbers from 1 to 10 are printed.

Now we shall print numbers from 50 to 40

Change n = 1 to n = 50

In other words as long as n is greater than or equal to 40. So change the condition to n greater than or equal to 40.

So Change n=n + 1 to n=n - 1

the numbers 50 to 40 has been printed

Now we shall print the first 10 multiples of 7.

Change n >= 40 to n <= 70

Change n = n – 1 to n = n + 7

So change n = 50 to n = 7and then end with 70.

Change the condition to n less than equal to 70

This way, we make sure the loop stops at 70.

So, change n=n - 1 to n=n + 7

This way first 7 is printed and n becomes 14, 14 is printed and so on untill 70. Save and run

We can also use a while loop to get the sum of digits of a number.

Let us see how to do so.

int n equal to 13876. This is the number

n greater than 0 open close bracket

The reason for using this condition will be evident in a while.

dSum = dSum + (n % 10);

n = n / 10;

To do that we use modulo operator.

Type dSum = dSum + (n % 10) So we get the unit digit and add it to dsum

 n = n / 10

n will become 138.

So on, as the loop progresses, the digits will be removed from n and finally

 n   become zero.After that the condition n greater than 0 will be false and the loop will stop

save and run. Point to output

Let us see the code and action. Save and run

As we can see the sum of digit which is 25 has been printed

Slide 6

Summary

In this tutorial we have learnt

• About while loop
• how to use it

Given a number, compute its reverse by using a while loop.

Example: 19435 => 53491

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