# 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 1st number starts with 2, 2nd 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.

### 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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