Java Program to Find the Sum of Natural Numbers using Recursion

In this article, we will understand how to find the sum of natural numbers using recursion. All possible positive numbers from 1 to infinity are called natural numbers. A recursive function is a function that calls itself multiple times until a particular condition is satisfied.

Recursion is the process of repeating items in a self-similar way. In programming languages, if a program allows you to call a function inside the same function, then it is called a recursive call of the function.

Many programming languages implement recursion by means of stacks. Generally, whenever a function (caller) calls another function (callee) or itself as callee, the caller function transfers execution control to the callee. This transfer process may also involve some data to be passed from the caller to the callee.

Below is a demonstration of the same −

Input

Suppose our input is −

Enter the number : 25

Output

The desired output would be −

The sum of natural numbers up to 25 is 325

Algorithm

Step 1 - START
Step 2 - Declare 2 integer values namely my_input and my_sum.
Step 3 - Read the required values from the user/ define the values
Step 4 - A recursive function ‘Add’ is defined which takes an integer as input and returns the sum of the input value and its previous value until the input value is reduced to 0.
Step 5 - The recursive function is called and the value ‘my_input’ is passed to it. Store the return value.
Step 6 - Display the result
Step 7 - Stop

Example 1

Here, the input is being entered by the user based on a prompt. You can try this example live in ourcoding ground tool .

import java.util.Scanner;
public class NaturalNumbers {
   public static void main(String[] args) {
      int my_input, my_sum;
      System.out.println("Required packages have been imported");
      Scanner my_scanner = new Scanner(System.in);
      System.out.println("A reader object has been defined ");
      System.out.print("Enter the number : ");
      my_input = my_scanner.nextInt();
      System.out.println("The number is defined as " +my_input);
      my_sum = Add(my_input);
      System.out.println("The sum of natural numbers up to " + my_input + " is " + my_sum);
   }
   public static int Add(int my_input) {
      if (my_input > 0)
         return my_input + Add(my_input - 1);
      else
         return my_input;
   }
}

Output

Required packages have been imported
A reader object has been defined
Enter the number : 25
The number is defined as 25
The sum of natural numbers up to 25 is 325

Example 2

Here, the integer has been previously defined, and its value is accessed and displayed on the console.

public class NaturalNumbers {
   public static void main(String[] args) {
      int my_input, my_sum;
      my_input = 25;
      System.out.println("The number is defined as " +my_input);
      my_sum = Add(my_input);
      System.out.println("The sum of natural numbers up to " + my_input + " is " + my_sum);
   }
   public static int Add(int my_input) {
   if (my_input > 0)
      return my_input + Add(my_input - 1);
   else
      return my_input;
   }
}

Output

The number is defined as 25
The sum of natural numbers up to 25 is 325