CODEWITHSUNDEEP
javainputjava.util.scanneroutputquadratic
user2288274
user2288274

Reputation: 1

quadratic formula with scanner inputs

Okay so I am a complete Java noob, and I'm trying to create a program for class that runs a quadratic equation using scanner inputs. So far what I've got is this:

import java.util.*;

public class QuadraticFormulaSCN {


public static void main(String[]args) {
  System.out.println("insert value for a:");
  Scanner scan1 = new Scanner(System.in);
   double a = scan1.nextDouble();
    System.out.println("insert value for b:");
  Scanner scan2 = new Scanner(System.in);
    double b = scan2.nextDouble();
    System.out.println("insert value for C:");
  Scanner scan3 = new Scanner(System.in);
   double c = scan3.nextDouble();

    double answer =((Math.sqrt(Math.pow(b,2)-(4*a*c))-b)/2);
      double final2 =(-b + Math.sqrt(Math.pow(b,2)-(4*a*c)))/2;
  System.out.println("The x values are:" + answer + final2);
}
}

But I get a weird output, specifically NaNaN... What do I do to fix this? What am I doing wrong?

Upvotes: 0

Views: 35989

Answers (5)

Quintinium
Quintinium

Reputation: 7

One thing I always try to do is put all my math in appropriate parenthesis to avoid an, all too easy, Order of Operations mistake. The NaN is saying "Not a number." You would also get that message if the user input numbers that could not produce a result, such as a trying to get the square root of a negative number. Also, just as a note, you can save sometime by only using on Scanner for a,b, and c. 

public class QuadraticFormula{

   public static void main(String[] args){
      java.util.Scanner input = new java.util.Scanner(System.in);
      double a = input.nextDouble();
      double b = input.nextDouble();
      double c = input.nextDouble();

      double quadPos = (-b + Math.sqrt(Math.pow(b,2)-(4*a*c)))/(2*a);
      double quadNeg = (-b - Math.sqrt(Math.pow(b,2)-(4*a*c)))/(2*a);

      System.out.println("-b - = " + quadNeg + "\n-b + = " + quadPos);

      }
   }

Upvotes: 0

DeltaLima
DeltaLima

Reputation: 5944

NaN is something you get when the calculation is invalid. Such as dividing by 0 or taking the squareroot of -1.

When I test your code with a = 1, b = 0 and c = -4 the answers is 2.02.0

The formatting is not right and the calculation of final2 is not negated.

Otherwise the code is right.

To improve you could check whether the discriminant is negative. 

double d = b*b -4 * a * c;
if (d < 0){
   System.out.println("Discriminant < 0, no real solutions" );
   return;
}
double x1 = (-b  -sqrt(d))/(2*a);
double x2 = (-b +sqrt(d))/(2*a);
System.out.format("The roots of your quadratic formula are %5.3f and %5.3f\n",x1,x2);

Or, if you prefer support for solutions from the complex domain:

if (d < 0) {
    System.out.println("Discriminant < 0, only imaginary solutions");
    double r = -b / (2 * a);
    double i1 = -sqrt(-d) / (2 / a);
    double i2 = sqrt(-d) / (2 / a);
    System.out.format("The roots of your quadratic formula are (%5.3f + %5.3fi) and (%5.3f + %5.3fi)\n",r, i1, r, i2);
    return;
}

Upvotes: 2

syb0rg
syb0rg

Reputation: 8247

I'm a little late to answer, but I corrected your problems (described in the other answers), fixed one of your calculations, and cleaned up your code.

import java.util.*;

public class Test {

    public static void main(String[] args)
    {
        Scanner s = new Scanner(System.in);
        System.out.println("Insert value for a: ");
        double a = Double.parseDouble(s.nextLine());
        System.out.println("Insert value for b: ");
        double b = Double.parseDouble(s.nextLine());
        System.out.println("Insert value for c: ");
        double c = Double.parseDouble(s.nextLine());
        s.close();

        double answer1 = (-b + Math.sqrt(Math.pow(b, 2) - (4 * a * c))) / (2 * a);
        double answer2 = (-b - Math.sqrt(Math.pow(b, 2) - (4 * a * c))) / (2 * a);

        if (Double.isNaN(answer1) || Double.isNaN(answer2))
        {
            System.out.println("Answer contains imaginary numbers");
        } else System.out.println("The values are: " + answer1 + ", " + answer2);
    }
}

Upvotes: 2

Ramiro Motteta
Ramiro Motteta

Reputation: 104

You should only do the calculation when discriminant is equal or greater than zero

if(((Math.pow(b,2)-(4*a*c))>= 0){ /* Calculation here */ } 
else {/*error message or complex number calculus*/};

Upvotes: 0

rgettman
rgettman

Reputation: 178253

You are getting NaN because you are attempting to take the square root of a negative number. In math that's not allowed unless you are allowing complex numbers, e.g. 1 +/- 2i.

This can happen in quadratic formulas when the discriminant (the thing in the square root) is negative, e.g. x^2 + 6*x + 100: b^2 - 4ac = 36 - 400 = -364. Taking the square root of a negative number in Java leads to NaN. (not a number)

To test for NaN, use Double.isNaN and handle the NaN appropriately.

In addition, your calculations are incorrect even if NaN isn't being encountered:

$ java QuadraticFormulaSCN
insert value for a:
1
insert value for b:
5
insert value for C:
6
The x values are:-2.0-2.0

This should have outputted 2.0 and 3.0

Upvotes: 1

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