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

| Welcome to the spoken tutorial on '''While Loop''' in java.

|  In this tutorial, you will learn: * about the '''while loop'''

* how to use it.

|  For this tutorial, we are using:

|  To follow this tutorial, you must have knowledge of '''relational operators in Java'''.

| If not, for relevant tutorials, please visit our website as shown. [http://spoken-tutorial.org]

| Here is the '''structure''' of a '''while loop'''.  

|  Let us now look at an example. Switch to '''Eclipse'''.

| Here, we have the '''eclipse IDE''' and  the skeleton  required  for rest of the code.

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

|  | We shall print numbers from '''1''' to '''10''' using a '''while loop'''. Type: '''int n = 1'''.

|  This variable 'n' is going to be our '''loop variable'''.

|  Type: '''while''' in parenthesis '''n''' less than or  equal to '''10''' open and close braces.

| This condition is called '''looping running condition'''.

| 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' becomes greater than 10.

| Inside the '''loop''', we shall print the value of 'n'.  

| '''System.out.println(n);''' and then increment '''n = n + 1;'''

| This way, first 1 is printed and then the value of 'n' becomes 2.  

| Then the '''loop condition''' is checked.

| Since it is true, 2 is printed and n becomes 3.

|  And so on.. loop progresses until 10 is printed. After that 'n' becomes 11 and the condition is not true and the '''loop''' will stop.

|  So, let us see the code in action.

|  '''Save''' and  '''run'''.

| Now we shall  print numbers from '''50''' to '''40'''.

|  So, we start with 50.   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.

| And since we are looping from a bigger number to a smaller number, we have decremented the loop variable.

| So Change '''n=n+1''' to '''n=n-1'''.

| '''Save''' and '''run'''. As we can see, the numbers 50 to 40 have been printed.

|  To do that, we start with 7.

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

| Change the condition to '''n''' less than equal to '''70'''.

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

| To get the multiples, we shall increment the '''loop variable''' by 7.

|So, change '''n=n-1''' to '''n= n+7'''.

|  This way, first 7 is printed and  then 'n' becomes 14, 14 is printed and so on until 70. '''Save''' and '''run'''.

|  | As we can see, the first 10 multiples of 7 are  printed.

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

| First, clear the '''main method'''.

|-

| '''int n''' equal to '''13876'''. This is the number.

| Then '''int dSum''' equal to '''0''' The variable '''dsum''' with symbolic for digit sum will contain the sum of digits.

|  Type: '''while n''' greater than '''0''' open close parenthesis.

| To do that, we use '''modulo operator'''.  

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

|After that  we remove the digit by dividing by 10. n = n / 10

| So when the '''loop''' is  '''run''' for the first time, '''dSum''' will be 6 and 'n' will be 1387.

| And when the loop is '''run''' for the second time, '''dSum''' will be sum of 7 and 6 which is 13 and 'n' will become 138.

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

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

| So, let us now add a print statement:

| '''System.out.println(dSum)'''

| Let us see the code and action. '''Save''' and '''run'''.

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

| This way, a '''while loop''' which is one of the most fundamental '''constructs''' in programming, can be used.

|  This brings us to the end of the tutorial.  

| In this tutorial, we have learnt:

* How to use it.

| As an assignment for this tutorial, solve the following problem.

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