I am getting NaN for an answer to my quadratic equation calculator- JAVA

Question

This is my main class:

import java.util.Scanner;

public class calc {
public static void main(String[] args){
    Scanner variablea = new Scanner(System.in);
    Scanner variableb = new Scanner(System.in);
    Scanner variablec = new Scanner(System.in);
    int a1, b1, c1;
    System.out.println("enter your 'A' variable");
    a1 = variablea.nextInt();
    System.out.println("enter your 'B' variable");
    b1 = variableb.nextInt();
    System.out.println("enter your 'C' variable");
    c1 = variablec.nextInt();

    algorithm algorithmObject = new algorithm();
    algorithmObject.algorithm(a1, b1, c1);

}

}

and this is the second one

      public class algorithm{
public void algorithm(int a, int b, int c){
    double x1;
    double square = Math.sqrt(b*b - 4*a*c);
    double numerator = b*-1 + square;
    double finalanswer = numerator/2*a;

    System.out.println(finalanswer);
}

}

Eclipse doesn't give me any errors, but after it asks for my 3 variables and I enter them, it just gives NaN. Any idea what I have done wrong?

Answer 1

There are issues with the code but the culprit is most likely this line:

double square = Math.sqrt(b*b - 4*a*c);

If b*b - 4*a*c is negative (there is no solution to the equation) then square is NaN and every computation involving it will be NaN as well. You can check it here.

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You could improve your calculator by first checking if b*b - 4*a*c < 0 and if it is so then you could write to the console that there is no real solution (and of course stop the computations there).

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I would change public void algorithm(int a, int b, int c) to

public void algorithm(double a, double b, double c)

Integer arithmetic can surprise you when you least expect it and I see no reason why a, b and c should be constrained to be int-s.

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OK, hope this helped.