Write a program in Java to display the n terms of even natural number and their sum

Improve Article

Save Article

Improve Article

Save Article

Print first N natural numbers using an iterative approach i.e. using for loop. For loop has three parameters initialization, testing condition, and increment/decrement.

Input:     N = 10
Output:    First 10 Numbers = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
           Sum of first 10 Natural Number = 55

Input:     N = 5
Output:    First 5 Numbers = 1, 2, 3, 4, 5
           Sum of first 5 Natural Number = 15

Approach

1. Start for loop initialization with i = 1.
2. Write testing condition as i <= N.
3. Add increment statement as i++ or i+=1.
4. Initialize a variable sum with 0.
5. Start adding i with the sum at each iteration of for loop and print i.
6. Print sum at the end for loop. 
    

Below is the implementation of above approach

Java

import java.io.*;

class GFG {

    public static void main(String[] args)

    {

        int N = 10;

        int sum = 0;

        System.out.print("First " + N + " Numbers = ");

        for (int i = 1; i <= N; i++) {

            System.out.print(i + " ");

            sum += i;

        }

        System.out.println();

        System.out.println("Sum of first " + N

                           + " Natural Number = " + sum);

    }

}

Output

First 10 Numbers = 1 2 3 4 5 6 7 8 9 10 
Sum of first 10 Natural Number = 55

Time Complexity: O(n)

Alternate Approach

1. Start for loop initialization with i = 1.
2. Write testing condition as i <= N.
3. Add increment statement as i++ or i+=1.
4. Start Printing i for each iteration.
5. Print sum using first N natural number formula at the end of for loop.

Below is the implementation of the above approach

Java

import java.io.*;

class GFG {

    public static void main(String[] args)

    {

        int N = 5;

        System.out.print("First " + N + " Numbers = ");

        for (int i = 1; i <= N; i++) {

            System.out.print(i + " ");

        }

        System.out.println();

        System.out.println("Sum of first " + N

                           + " Natural Number = " + (N*(N+1))/2);

    }

}

Output

First 5 Numbers = 1 2 3 4 5 
Sum of first 5 Natural Number = 15

Time Complexity: O(n)

Auxiliary Space: O(1) as it is using constant space for variables