Java Programming - divisibility and counting?

Question

I am a student trying to learn programming on my own, getting help from online sources and people like you. I found an exercise online to create a small program that will do this:

Write a program that will read the numbers a and b (type long) and list how many numbers between a and b are divisible by either 2, 3 or 5.

For example:

a=11 b=30 The counter would be 14, since there are 14 numbers divisible by 2,3 or 5 in between: 12, 14, 15, 16, 18, 20, 21, 22, 24,25, 26, 27, 28, 30

This is what I have already tried, but it doesn't seem to work. I would need your guidance and help to finish this. Thank you for your time and your hard work in advance.

import java.util.Scanner;

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

        long a = sc.nextLong();
        long b = sc.nextLong();

        for (long c = a; c <= b; c++) {
            if (c%2 || c%3 || c%5) {
                System.out.println(c);
            }
        }
    }
}

CURRENT STAGE OF THE PROGRAM:

import java.util.Scanner;

public class Test2 {
    public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);

    long a = sc.nextLong();
    long b = sc.nextLong();

    long count = 0; // counter

    for (long c = a; c <= b; c++) {
        if (c % 2 == 0 || c % 3 == 0 || c % 5 == 0) {
            count++;
            System.out.println(c);
            }

        }
    }

}

There is still a thing to do:

Now it lists me the numbers which are divisible by 2,3 or 5. But all I need is one single number that will count how many numbers there is.

Answer 1

You're on the right way - you just need to turn your modulo expression into condition - i.e., check that the remainder is actually 0. Also, you should separate between the loop variable and the counter of the results:

long c = 0; // counter
for(long l = a; l <= b; l++) {
    if (l % 2 == 0|| l % 3 == 0 || l % 5 == 0) {
        ++c;
    }
}
System.out.println(c);

Answer 2

c%2 returns a integer, not a boolean.

You have to check if (c%2==0 || ...)

Answer 3

I would say it does not even compile:

if(c%2 || c%3 || c%5)

c%2 deos not evaluate to a boolean in java, unlike in C or C++;

You have to use the equal operator ==

if(c%2 == 0 || c%3 == 0 || c%5 == 0)

Answer 4

Try this:

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

    long a = sc.nextLong();
    long b = sc.nextLong();

    int count = 0; // counter

    for (long c = a; c <= b; c++) {
        if (c % 2 == 0 || c % 3 == 0 || c % 5 == 0) {//this where the error is in your program
            count++;
            System.out.println(c);//you are printing c and you are not maintaining the counter
        }
    }
    System.out.println("Counter is " + count);
}

Answer 5

Try this code:

 for(int i=a;i<=b;i++){
  if(i%2 == 0 || i%3 == 0 || i%5 == 0){
    c++;
  }
 }

Answer 6

I would go back and learn about modular arithmetic. Assuming c = 9, c%5 = 4. How is that suppose to be interpreted as a boolean?

In your code you could have an expression like "if(c%2 || c%3 || c%5)" which, assuming c=9, translates to if(1 || 0 || 4). In Java, conditionals need to be written as boolean expressions. You need to write them so your answers can explicitly be true or false.

The right way would be:

if((c % 2 == 0) || (c % 3 == 0) || (c % 5 == 0))

As for counting the number of numbers, use a separate variable and increment if the conditional is true.