Thread: What is wrong with this code ( an exercise )

So the exercise tells me to get the values a, b and c from the user and then use the quadratic formula to get both roots.

if both are above 0, display both roots
if both are 0, display 1 root
if both are negative, no real root

So all is good until this:

if (root1 && root2 > 0) {
System.out.println("The equation has two roots: " + root1 + " and " + root2);
else if(root1 && root2 == 0) {
System.out.println("The equation has one root: " + root1);
}
}else{
System.out.println("The equation has no real roots");
}

if i only placed the braces on if and else (but not else if) the compiler doesn't recognise else and wants it disposed, if i place the braces on all, it says i cant convert double into int even tho i didnt specify anything of the sort.

Could you guys help me out ? much thanks!

Please edit your post and wrap your code with code tags:

[code]
**YOUR CODE GOES HERE**
[/code]

to get highlighting and preserve formatting.

Start with the first { and find its matching }
There is a } on line 1. Where is its matching }?

Do the same with the if and else.
There is an if on line 1, where is its matching else?

Please copy the full text of the error message and paste it here. It has important info about the error.

The operator && is undefined for the argument type(s) double, boolean

The && operator works with two boolean operands: boolean1 && boolean2
In the expression:
root1 && root2 == 0
Only the expression: root2 == 0 has a boolean value
root1 is a double and not a boolean
To fix the error, change the first operand to a boolean. For example: x > 3

Exception in thread "main" java.util.NoSuchElementException
at java.util.Scanner.throwFor(Scanner.java:862)
at java.util.Scanner.next(Scanner.java:1485)
at java.util.Scanner.nextDouble(Scanner.java:2413)
at ChapterThree.main(ChapterThree.java:10)

At line 10 the program calls the nextDouble method but there isn't any double value available.

What was entered for the Scanner class's nextDouble method to read?

This had nothing to do with your problem but is provided for your reading pleasure. From the Wiki on the quadratic formula.

Regards,
Jim


Avoiding loss of significance

Although the quadratic formula provides an exact solution, the result is not exact if real numbers are approximated during the computation, as usual in numerical analysis, where real numbers are approximated by floating point numbers (called "reals" in many programming languages). In this context, the quadratic formula is not completely stable.

This occurs when the roots have different order of magnitude, or, equivalently, when b² and b² − 4ac are close in magnitude. In this case, the subtraction of two nearly equal numbers will cause loss of significance or catastrophic cancellation in the smaller root. To avoid this, the root that is smaller in magnitude, r, can be computed as (c/a)/R where R is the root that is bigger in magnitude.

There is a way to use the Scanner class that does not require a console: Put the input values into the Scanner class's constructor:

 Scanner input = new Scanner("3.4 5.6 7.8"); //  Load 3 floating numbers to read with nextDouble