import java.util.Scanner; /** * calculates sum of odd integers from 1 to n, with n being a user given odd positive integer */ public class OddSum { /** * recursively finds sum of odd integers from 1 to n * @param int n determines when to stop adding * @return returns sum */ public static int oddSum(int n) { if (n == 1) { return 1; } else { return oddSum(n - 2) + n; } } public static void main(String[] args) { int n, value; Scanner in = new Scanner(System.in); System.out.println("Give me a positive odd integer n and I'll give you the sum of odd integers from 1 to n."); System.out.print("n? "); if (!in.hasNextInt()) { //checks if user input is int String wrong = in.next(); System.err.printf("%s is not an integer.\n", wrong); return; } n = in.nextInt(); if (n <= 0 || n % 2 == 0) { //checks if user input is positive and odd System.err.println("This integer is either negative or even."); return; } value = oddSum(n); System.out.println(value); } }