CODEWITHSUNDEEP
java
Baxter Lopez
Baxter Lopez

Reputation: 1139

Mod ignored by java compiler

I have a problem with a program that prints a list of prime numbers, but as modulus is ignored, the program is not working. Can someone find something wrong here?

import java.util.Scanner;


public class Primos {

    public static void main(String[] args){
        Scanner entrada = new Scanner(System.in);
        System.out.println("Dame el numero hasta el cual sacare primos");
        int hasta = entrada.nextInt();

        for(int actual = 2 ; actual <= hasta ; actual++){
            boolean primo = true;
            for(int probando = 2 ; probando < actual ; probando ++){
                double valor = (double)actual/(double)probando;
                System.out.println("1." +valor);
                valor = valor % 10;
                System.out.println("2." +valor);
                if(valor == 0){
                    primo = false;
                    break;
                }
            }

            if(primo)
                System.out.println("El numero " + actual + " es primo");
        }
    }   
}

prints

Dame el numero hasta el cual sacare primos
3
El numero 2 es primo
1.1.5 <before mod
2.1.5 < after mod
El numero 3 es primo

Upvotes: 0

Views: 97

Answers (4)

TheKojuEffect
TheKojuEffect

Reputation: 21101

As mentioned in assylias's comment, 1.5 % 10 = 1.5

Replace your statement

valor = valor % 10;

with

valor = valor - (long) valor;

Upvotes: 1

Joop Eggen
Joop Eggen

Reputation: 109613

It should be

int valor = actual % probando;

As actual / probando gives the integer division (rounding down / truncating the fraction), actual % probando gives the remainder of such division:

12 / 7 = 1
12 % 7 = 5


(p / q) * q + (p % q) == p

If value is 0, probando is a divisor of actual. What you meant.

Upvotes: 0

Alcanzar
Alcanzar

Reputation: 17165

Your logic is wrong. A number is prime if no number less than it divide evenly into it (ie number % factor == 0 means it's not prime)

public static void main(String[] args){
    Scanner entrada = new Scanner(System.in);
    System.out.println("Dame el numero hasta el cual sacare primos");
    int hasta = entrada.nextInt();

    boolean primo = true;
    for(int factor = 2 ; primo && factor < hasta/2 ; factor++){
      primo = hasta % factor != 0;
    }
    if(primo)
      System.out.println("El numero " + actual + " es primo");
    }
}

Upvotes: 0

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 280138

In your first iteration, the nested for loop doesn't execute because actual=2 is not smaller than probando=2.

for (int probando = 2; probando < actual; probando++) {

So your next iteration occurs where actual=3 and probando=2, printing the values you see.

Upvotes: 0

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