Do you have to read in the entire formula? Or can you ask the user for separate values? The latter is going to be much much easier.
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
System.out.println("Enter a: ");
double a = scan.nextDouble();
System.out.println("Enter b: ");
double b = scan.nextDouble();
System.out.println(Enter c: ");
double c = scan.nextDouble();
// compute quadratic ...
}
If you must extract all the numbers from a single string, then you can still use the Scanner so long as they are separated somehow (usually spaces), and there is nothing else in the string.
String values = "1.0 2.3 4.5"; // a = 1, b = 2.3, c = 4.5
Scanner reader = new Scanner(values);
double a = values.nextDouble();
double b = values.nextDouble();
double c = values.nextDouble();
However, if the given string is like this:
"1.0X^2 + 3.5X + 2 = 0"
, you'll have an extremely hard time extracting the numbers you want. It's not impossible, but I doubt that's what your teacher wants from you. If you really want to know, try doing a google search on regular expressions.