Quadratic equations solver in java

Question

I tried and succeed to build a quadratic equation solver.

public class Solver {
public static void main (String[] args) {
int a = Integer.parseInt(args[0]);
int b = Integer.parseInt(args[1]);
int c = Integer.parseInt(args[2]);
double positive = (-b + Math.sqrt(b*b-4*a*c))/2*a;
double negative = (-b - Math.sqrt(b*b-4*a*c))/2*a;
System.out.println("First answer is " + positive);
System.out.println("Second answer is " + negative);
} 
}

Sometimes I get NaN in the output. What did i do wrong?

Well what inputs did you give? I suspect you gave values such that there *are* no solutions. (i.e. b^2 - 4ac is negative.) — Jon Skeet, May 18 '14 at 11:13
You need to handle the cases of `a=0` and `b*b-4*a*c` is negative. — BobTheBuilder, May 18 '14 at 11:13
I would declare a, b and c as `double`, sometimes you can get integer / double aritmetic clash (especialy when you divide), but this doesnt seem to be the case. — kajacx, May 18 '14 at 11:18
possible duplicate of [Quadratic Formula Program - getting NaN error](http://stackoverflow.com/questions/20753021/quadratic-formula-program-getting-nan-error) — ΔȺȾΔ, May 18 '14 at 11:28
You need to put the denominator in parentheses: `x/2*a -> x/(2*a)` — Stefan, May 18 '14 at 11:30

Artur Malinowski · Answer 1 · 2014-05-18T11:40:51.423

NaN - not a number - is a value, that represents the result of invalid mathematical operations. Using real numbers, you cannot compute a square root of negative number - so NaN is returned.

Another problem with your solution is /2*a fragment. Division and multiplication have equal priority, so parenthesis are necessary. Moreover, if a is equal to zero, Java will throw java.lang.ArithmeticException: / by zero - you need also to check it.

One possible solution will be:

if (a == 0) {
    System.out.println("Not a quadratic equation.");
    return;
}

double discriminant = b*b - 4*a*c;
if (discriminant < 0) {
    System.out.println("Equation has no ansewer.");
} else {
    double positive = (-b + Math.sqrt(discriminant)) / (2*a);
    double negative = (-b - Math.sqrt(discriminant)) / (2*a);
    System.out.println("First answer is " + positive);
    System.out.println("Second answer is " + negative);
}

Thank you. Did you ment the first double to be discriminant? — Rona, May 18 '14 at 11:31

score 0 · Answer 2 · answered May 18 '14 at 11:23

0

NaN stands for Not a Number. You have entered inputs that caused a mathematically undefined operation. so if the first number "a" is zero you will get that, and if b*b is greater than 4*a*c you will also get that message, the first situation is division by zero and the second is calculating the root of negative number.

answered May 18 '14 at 11:23

Ahmed Wahbi

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How can I prevent Nan? – Rona May 18 '14 at 11:24

Quadratic equations solver in java

2 Answers2