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## Program to Calculate the Sum of Natural Numbers

Natural numbers are the numbers 1, 2, 3, 4… which are also called counting numbers. These are basically whole numbers except 0.

We can find the sum of natural numbers in Java using the following methods-

- Sum of natural numbers using while loop
- Sum of natural numbers using for loop
- Sum of natural numbers using formula
- Sum of natural numbers using recursion
- Sum of natural numbers between a range using an user defined function(do-while loop)

### Method-1 : Sum of natural numbers using while loop

We will be taking the last element as input from the user and run the while loop while our counter is less than the number.

Let’s see the below program to understand it more clearly.

import java.util.Scanner; class sumNatural { public static void main(String args[]) { System.out.println("Enter the last element"); //Taking input from user Scanner scan = new Scanner(System.in); int num = scan.nextInt(); int i=0, sum=0; while(i<=num) { //Iterating the counter for each iteration //and adding the value to the previously existing sum. sum+=i; i++; } System.out.println("The sum of natural numbers including "+num+" is "+sum); } }

Output: Enter the last element 50 The sum of natural numbers including 50 is 1275

### Method-2 : Sum of natural numbers using for loop

Like the previous example we will be taking the last element as input from the user and run the for loop but, here we won’t have to use another iterator. The for loop iterator will do the work.

Let’s see the below program to understand it more clearly.

import java.util.Scanner; class sumNatural { public static void main(String args[]) { System.out.println("Enter the last element"); //Taking input from user Scanner scan = new Scanner(System.in); int num = scan.nextInt(); int sum=0; for(int i=1;i<=num;i++) { //adding the iterator valueto the prevously existing sum. sum+=i; } System.out.println("The sum of natural numbers including "+num+" is "+sum); } }

Output: Enter the last element 50 The sum of natural numbers including 50 is 1275

### Method-3 : Sum of natural numbers using formula

We can also find the sum of natural numbers using the math formula.

Sum = n(n+1)/2;

Let’s see the below program to understand it more clearly.

import java.util.Scanner; class sumNatural{ public static void main(String args[]) { System.out.println("Enter the last element"); //Taking input from user Scanner scan = new Scanner(System.in); int num = scan.nextInt(); //Using the math formula to calculate the sum int sum=num*(num+1)/2; System.out.println("The sum of natural numbers including "+num+" is "+sum); } }

Output: Enter the last element 50 The sum of natural numbers including 50 is 1275

### Method-4 : Sum of natural numbers using recursion

** **We can find the sum of natural numbers using recursion inside an user defined function.

import java.util.Scanner; class sumNatural { public static int sumNumbers(int num) { //Recursive function if (num != 0) return num + sumNumbers(num - 1); else return num; } public static void main(String args[]) { System.out.println("Enter the last element"); //Taking input from user Scanner scan = new Scanner(System.in); int num = scan.nextInt(); //Using recursive function to calculate the sum System.out.println("The sum of natural numbers including "+num+" is "+sumNumbers(num)); } }

Output: Enter the last element 50 The sum of natural numbers including 50 is 1275

### Method-5 : Sum of natural numbers between a range using an user defined function(do-while loop)

We can find the sum of a particular range using a do-while loop inside a user-defined function. We have to set the counter to the lower limit of the range.

import java.util.Scanner; class sumNatural { public static int sumNumbers(int lowerRange, int upperRange) { int sum = 0; do{ sum+=lowerRange++; }while(lowerRange!=upperRange); return sum; } public static void main(String args[]) { int lowerRange = 10, upperRange = 90; System.out.println("The sum of natural numbers from "+lowerRange+" and "+upperRange+" is "+sumNumbers(lowerRange,upperRange)); } }

Output: The sum of natural numbers from 10 and 90 is 3960

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