Java Program to Find the Sum of Series 2-4+6-8+…-/+N

In the previous article, we have discussed about Java Program to Find the Sum of Series (a*2) + (a*3) + (a*4) + …… + N

In this article we are going to see how to find sum of the series 2-4+6-8+…-/+N by using Java programming language

Java Program to Find the Sum of Series 2-4+6-8+…-/+N

On observing the pattern carefully, we can see first number is positive and second number is negative.

While 1^st number starts with 2, 2^nd number is 2 added with previous number.

Example:

X = 2

N = 20

2 – 4 + 6 – 8 + …… – 20 = -10

Let’s see different ways to find sum of the series 2-4+6-8+…-/+N.

By Using for Loop
By Using while Loop
By Using User Defined Method

Method-1: Java Program to Find the Sum of Series 2-4+6-8+…-/+N By Using For Loop

Approach:

Declare an integer variable say ‘n’ which holds the last term of the series.
Create Scanner class object.
Prompt the user to enter a number as value of n.
Declare an integer variable say ‘sum ‘and initialize it with 0.
Use a for loop from i =1 to i<=n/2
Inside for loop we will first check the index of i, if i is even then we will subtract i*2 from sum Else we will add i*2 in sum.

Print the result.

Program:

import java.util.*;
public class Main
{
    public static void main(String args[])
    {
        //creating object of Scanner class 
        Scanner s = new Scanner(System.in);
        //Taking input of number of elements in the series
        System.out.println("Enter the value of last number 'n' ");
        int n = s.nextInt();
        //for loop to print the series
        int sum = 0;
        for (int i = 1; i <= n/2; i++) 
        {
            if (i % 2 == 0) 
                sum -= i * 2;
            else
                sum += i * 2;
        } 
        System.out.println("Sum of the series is " + sum);
    }
}

Output:

Enter the value of last number 'n' 
20
Sum of the series is -10

Method-2: Java Program to Find the Sum of Series 2-4+6-8+…-/+N By Using While Loop

Approach:

Declare an integer variable say ‘n’ which holds the last term of the series.
Create Scanner class object.
Prompt the user to enter a number as value of n.
Declare an integer variable say ‘sum ‘and initialize it with 0.
Declare an integer variable i and initialize it with 1.
Continue a while loop till i<=n/2
Inside while loop we will first check the index of i, if i is even then we will subtract i*2 from sum Else we will add i*2 in sum.

Print the result.

Program:

import java.util.*;
public class Main
{
    public static void main(String args[])
    {
        //creating object of Scanner class 
        Scanner s = new Scanner(System.in);
        //Taking input of number of elements in the series
        System.out.println("Enter the value of last number 'n' ");
        int n = s.nextInt();
        // while loop to print the series
        int sum = 0;
        int i = 1;
        while(i <= n/2)
        {
            if (i % 2 == 0) 
                sum -= i * 2;
            else
                sum += i * 2;
            i++;
        }
        System.out.println("Sum of the series is " + sum);
    }
}

Output:

Enter the value of last number 'n' 
40
Sum of the series is -20

Method-3: Java Program to Find the Sum of Series 2-4+6-8+…-/+N By Using User Defined Method

Approach:

Declare an integer variable say ‘n’ which holds the last term of the series.
Create Scanner class object.
Prompt the user to enter a number as value of n.
Then call a user defined method say m1() and pass n as parameter.
Inside method declare an integer variable say ‘sum ‘and initialize it with 0.
Use a for loop from i =1 to i<=n/2
Inside for loop we will first check the index of i, if i is even then we will subtract i*2 from sum Else we will add i*2 in sum.

Print the result.

Program:

import java.util.*;
public class Main
{
    public static void main(String[] args)
   {
        // creating object of scanner class 
        Scanner s = new Scanner(System.in);
        //Taking input of number of elements in the series
        System.out.println("Enter the value of last exponent 'n' ");
        int n = s.nextInt();
       // calling m1 method to print the series
        m1(n);
   }
    public static void m1(int n)
    {
        //for loop to print the series
       int sum = 0;
        for (int i = 1; i <= n/2; i++) 
        {
            if (i % 2 == 0) 
                sum -= i * 2;
            else
                sum += i * 2;
        } 
        System.out.println("Sum of the series is " + sum);
    }
}

Output:

Enter the value of last exponent 'n' 
10
Sum of the series is 6

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