Making loops in order to test values

Question

I need help making a loop that looks at each value from 1 to number-1. Also how to test each value to see if it is a divisor of number, and if it is, adding it to the sum.

This is what I have so far:

public static void main(String[] args) {
  Scanner input = new Scanner (System.in);

  System.out.print("Please enter a positive integer: ");
  int n = input.nextInt();

  while (n < 0) {
    System.out.println(n + " is not positive.");
    System.out.print("Please enter a positive integer: ");
    n = input.nextInt();
  }
}

If `n` is a positive number then your loop will run forever. You need a running index to start from 1 and a loop that runs while it's smaller than `n`. Did you learn about loops? You must have seen examples. — user1803551, Feb 08 '16 at 06:27

JD9999 · Answer 1 · 2016-02-08T20:46:47.037

You can use this as a starting block for your application:

    package Testers;

import java.io.Console;

public class Application {

    public static void main(String[] args)
    {
        Console console = System.console();
        if (console == null) 
        {
            System.err.println("No console.");
            System.exit(1);
        }

        boolean keepRunning = true;
        while (keepRunning)
        {       
            String name =  console.readLine("Type your positive integer");
            try{
            int integer = Integer.parseInt(name);
            if(integer < 0){
                System.out.println("You must specify a positive integer!");
            }
            for(int i = 1; i<integer; i++){ 
                // our variable "i" is smaller than "integer". This will parse all the numbers between one and "integer" -1.
                if(i % 2 == 0){
                    //"i" IS divisible by 2. Of course, you can change this value to what you want to change it to.
                    //Here you can add it to a sum
               }else{
                //"i" is not divisible by 2. Of course, you can change this value to what you want to change it to.
                }
            }
            }catch(NumberFormatException e){
                System.out.println("You must specify a positive integer!");
            }
        }
    }   

}

(1) Use a `Scanner` instead of `Console` as it might not be available. (2) No need for `int one = 1` when it can be assigned directly to `i`. (3) Format your code properly. — user1803551, Feb 08 '16 at 10:16
Edited indenting and removed the "one" variable. I have never had a problem using `Console` instead of `Scanner`, I am reluctant to change that. Thank you for your help! — JD9999, Feb 08 '16 at 20:47

score 0 · Answer 2 · answered Feb 08 '16 at 21:04

If you want to do something for a known number of times, it is mostly a good idea to use a for loop. If you want to do something for number 1 to n-1, the loop could look like

for(int i = 1; i < n; i++) { // do stuff }

Note that it starts counting from 1 and stops as soon as i is greater or equal than n.

In order to know whether a number, say n, is divisible by some number, say k, the modulo-operator % could be used. If n % k == 0 this means that n is divisible by k. With an if-statement this can be tested and when you have some sum variable you can add whatever you want to that variable to sum things up.

Hope that helps

Making loops in order to test values

2 Answers2