Looping Statements

It is the type of the control flow statement which will execute the group of statements multiple times by checking the condition in each time.
Looping statement is classified into 1) for loop 2) while loop 3) do while loop

1) for loop

It is the type of looping statements which will have fix initial and final point to execute the given statements multiple times.
Syntax
Que1 Print “*” four times.

class Que1
{
    public static void main(String[]args)
    {
        for (int i = 0; i < 4; i++)
        {
            System.out.println("*");
        }
    }
}

Ans =
*
*
*
*
*
Que2 Write the program to print even number between 100 to 80 using for loop.

class Que2
{
    public static void main(String[]args)
    {
        for (int i = 100; i >= 80; i--)
        {
            if (i % 2 == 0)
            {
                System.out.println(i);
            }
        }
    }
}

Ans =
100
98
96
94
92
90
88
86
84
82
80
Que3 Write the program to find summation of first ten numbers starting from 1.

class Que3
{
    public static void main(String[]args)
    {
        int sum = 0;
        for (int i = 1; i <= 10; i++)
        {
            sum = sum + i;
        }
        System.out.println(sum);
    }
}

Ans = 55
Que4 Write the program to find summation of all even numbers between 20 to 10 using for loop.

class Que4
{
    public static void main(String[]args)
    {
        int sum = 0;
        for (int i = 20; i >= 10; i--)
        {
            if(i % 2 == 0 )
            {
                sum = sum + i;
            }
        }
        System.out.println(sum);
    }
}

Ans = 90

2) while loop

It will execute the group of statements multiple times until condition is true.
while loop first check the condition if it is true then it will execute the statements.

Syntax

while (condition)
{
  statements;
  update;
}

flowchart
eg.

 class Program 1
 {
     public static void main (String [] args)
     {
         while (false)
         {
             System.out.println("Hello World")
         }
     }
 }

Ans = Unreachable Statement (Compile Time Error)

 class Program2
 {
     public static void main (String [] args)
     {
         int i =0;
         while (i < 5)
         {
             System.out.println("*")
         }
     }
 }

Ans =
*
*
*
*
*
Que1 Write a program to print the numbers in reverse order from 20 to 10 using while loop

class Que1
{
    public static void main(String[]args)
    {
        int i = 20;
        while (i >= 10)
        {
            System.out.print(i +" ");
            i--;
        }
    }
}

Ans = 20 19 18 17 16 15 14 13 12 11 10
Que2 Write a program to print all the even numbers between 25 to 50 using while loop

class Que2
{
    public static void main(String[]args)
    {
        int i = 25;
        while (i <= 50)
        {
            if (i % 2 == 0)
            System.out.print(i +" ");
            i++;
        }
    }
}

Ans = 26 28 30 32 34 36 38 40 42 44 46 48 50
Que3 Write a program to print all the numbers which are divisible by 3 & 7 between 100 to 50

class Que3
{
    public static void main(String[]args)
    {
        int i = 100;
        while (i >= 50)
        {
            if (i % 3 == 0 && i % 7 == 0)
            System.out.print(i +" ");
            i--;
        }
    }
}

Ans = 84 63
Note
Increment/decrement always gives after completing decision making block.

3) do while loop

It is used to execute group of statements multiple times depending on condition.
do while loop executes atlest once even though condition is false.
do will first executes statements and then check the condition.
Syntax

do
{
    statements;
    update;
}
while(condition);

Note
In do while loop the while condition should be ended with semicolon (;).
In do while even if condition either true/false, the statement gets execute atlest onces.
eg.1

class Example1
{
    public static void main(String[]args)
    {
        int a = 0;
        do
        {
            System.out.print(a++);
        }
        while (a > 10);
    }
}

Ans = 0
Que1 Write a program to print all the numbers between 0 to 10 using do while loop.

class Que1
{
    public static void main(String[]args)
    {
        int a = 0;
        do
        {
            System.out.print(a +" ");
            a++;
        }
        while (a <= 10);
    }
}

Ans = 0 1 2 3 4 5 6 7 8 9 10
Que2 Write the difference between whie loop and do while loop.

No	while loop	do while loop
1.	Condition is tested at the beginning of the loop.	Condition is tested at the end of the loop.
2.	If condition is true then only statements will executed.	Even condition is true/false statements will executed at least once.
3.	In while loop condition should not be ended with (;) semicolon.	In do while loop condition should be ended with (;) semicolon.