Doubt while JAVA [duplicate]

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Doubt while JAVA [duplicate]

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#1 by (0 votes)

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Why, if I enter 4.95, does he return the 5 centimos and if I enter 1.95, he does not return it to me?

package ejer30;
import java.util.Scanner;

public class Expendedora {
    private double dinero;
    private static Scanner sc = new Scanner(System.in);

    public void setDinero() {
        dinero=sc.nextDouble();
    }

    public void calculaMonedas() {

        int cont2E=0;
        int cont1E=0;
        int cont50C=0;
        int cont20C=0;
        int cont10C=0;
        int cont5C=0;

        while (dinero>=2) {
            cont2E++;
            dinero=dinero-2;
        }

        while (dinero>=1) {
            cont1E++;
            dinero=dinero-1;
        }

        while (dinero>=0.50) {
            cont50C++;
            dinero=dinero-0.50;
        }

        while (dinero>=0.20) {
            cont20C++;
            dinero=dinero-0.20;
        }

        while (dinero>=0.10) {
            cont10C++;
            dinero=dinero-0.10;
        }

        while (dinero>=0.05) {
            cont5C++;
            dinero=dinero-0.05;
        }
            System.out.println("Monedas de 2€: "+cont2E);
            System.out.println("Monedas de 1€: "+cont1E);
            System.out.println("Monedas de 50 cent: "+cont50C);
            System.out.println("Monedas de 20 cent: "+cont20C);
            System.out.println("Monedas de 10 cent: "+cont10C);
            System.out.println("Monedas de 5 cent: "+cont5C);
    }       

    public static void main(String[] args) {
        Expendedora a = new Expendedora();
        System.out.println("Introduce dinero: ");
        a.setDinero();
        a.calculaMonedas();
    }
}

java

asked by David 14.11.2017 в 19:27

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1 answer

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score 0 · Accepted Answer

As I put you in the link marking this question as a duplicate ( Why can not my programs do arithmetic calculations correctly? ), the type float and double are not precise types. Even if dinero has a value of 0.05 , it may be that internally, the value is something like 0.04999999... , which would cause condition dinero>=0.05 to return false .

To avoid these precision problems with monetary values, you can use the type BigDecimal . Although it is more uncomfortable in its use, at least it is more accurate.

Here is an example of how your code could use BigDecimal :

public class Expendedora {
    private static final BigDecimal DOS_EUROS = new BigDecimal("2.00");
    private static final BigDecimal UN_EURO = new BigDecimal("1.00");
    private static final BigDecimal CINCUENTA_CENTAVOS = new BigDecimal("0.50");
    private static final BigDecimal VEINTE_CENTAVOS = new BigDecimal("0.20");
    private static final BigDecimal DIEZ_CENTAVOS = new BigDecimal("0.10");
    private static final BigDecimal CINCO_CENTAVOS = new BigDecimal("0.05");

    private BigDecimal dinero;
    private static Scanner sc = new Scanner(System.in);

    public void setDinero() {
        dinero=sc.nextBigDecimal();
    }

    public void calculaMonedas() {
        int cont2E=0;
        int cont1E=0;
        int cont50C=0;
        int cont20C=0;
        int cont10C=0;
        int cont5C=0;

        while (dinero.compareTo(DOS_EUROS) >= 0) {
            cont2E++;
            dinero=dinero.subtract(DOS_EUROS);
        }

        while (dinero.compareTo(UN_EURO) >= 0) {
            cont1E++;
            dinero=dinero.subtract(UN_EURO);
        }

        while (dinero.compareTo(CINCUENTA_CENTAVOS) >= 0) {
            cont50C++;
            dinero=dinero.subtract(CINCUENTA_CENTAVOS);
        }

        while (dinero.compareTo(VEINTE_CENTAVOS) >= 0) {
            cont20C++;
            dinero=dinero.subtract(VEINTE_CENTAVOS);
        }

        while (dinero.compareTo(DIEZ_CENTAVOS) >= 0) {
            cont10C++;
            dinero=dinero.subtract(DIEZ_CENTAVOS);
        }

        while (dinero.compareTo(CINCO_CENTAVOS) >= 0) {
            cont5C++;
            dinero=dinero.subtract(CINCO_CENTAVOS);
        }

        System.out.println("Monedas de 2€: "+cont2E);
        System.out.println("Monedas de 1€: "+cont1E);
        System.out.println("Monedas de 50 cent: "+cont50C);
        System.out.println("Monedas de 20 cent: "+cont20C);
        System.out.println("Monedas de 10 cent: "+cont10C);
        System.out.println("Monedas de 5 cent: "+cont5C);
    }       

    public static void main(String[] args) {
        Expendedora a = new Expendedora();
        System.out.println("Introduce dinero: ");
        a.setDinero();
        a.calculaMonedas();
    }
}