Write a program to print factorial of any number

import java.util.*;
class factorial
{
public static void main (String arg[])
{
Scanner in = new Scanner (System.in);

int a,b=1;
System.out.print ("\n\t Enter the number = ");
a=in.nextInt();

while (a>0)
{
b*=a;
--a;
}

System.out.println ("\n\t Factorial = "+b);

}
}

Note:
     First of all computer will check the condition of while loop. If it is true then it will
 multiply b by a. After that it will decrease the value of a by 1 and repeat the same task. This
 will continue until a=0. When a=0 the loop will be broken and the next statement to it will
be executed.

Write a program that print all odd numbers from 0 to a user specific number using do while loop

import java.util.*;
class odd
{
public static void main (String arg[])
{
Scanner in = new Scanner (System.in);
int a;
System.out.print ("\n\t Enter the ending number = ");
a=in.nextInt();

 

do
{
if (a%2!=0)
System.out.print ("\n\t "+a);
--a;
}while (a>0);

}
}

Note:

        In this program if we divide a by 2 and it do not returns 0, then it will be printed on
screen otherwise not.

Write a program to calculate sum and product of even numbers

import java.util.*;
class sumeven
{
public static void main (String arg[])
{
Scanner in = new Scanner (System.in);
int a,s=0,p=1;
System.out.print ("\n\t Enter the ending number = ");
a=in.nextInt();

while (a>0)
{
if (a%2==0)
{
s+=a;
p*=a;
}
--a;
}

System.out.println ("\n\t Sum of even numbers = "+s);
System.out.println ("\n\t Product of even numbers = "+p);
}
}

Note:
         In this program we have used two arithmetic operators in the body of if statement. First
is adding, whatever the value of a, in s and second is multiplying all values of a.

Write a program that print all even numbers from 0 to a given range

import java.util.*;
class even
{
public static void main (String arg[])
{
int a;
System.out.print ("\n\t Enter the number = ");
a=in.nextInt();

while (a>0)
{
if (a%2==0)
System.out.print ("\n\t "+a);
--a;
}

}
}

Note:
         In this program, body of the loop will be executed till a is greater than 0. As you have
noticed a conditional statement in the body of the loop, this is the actual code in our program
which is checking that either the number is even or odd.