Newbie Question

Ruby
1

Help I am completely new to ruby and to OO programming. Why-does my code
not compile??

class Quadratic

def findroots()
    b = (ARGV[0])
    c = (ARGV[1])
    $stdout.print("You entered " , ARGV[1], ARGV[0], "\n")
    discriminant = b * b - 4.0 * c
    sqroot =  Math.sqrt(discriminant)

    root1 = (-b + sqroot) / 2.0
    root2 = (-b - sqroot) / 2.0

    $stdout.print(root1)
    $stdout.print(root2)
end

end

if FILE == $0
qf = Quadratic.new
qf.findroots
end

2

On Mon, Feb 25, 2008 at 3:18 PM, Christian Rubio
[email protected] wrote:

    sqroot =  Math.sqrt(discriminant)

if FILE == $0
qf = Quadratic.new
qf.findroots
end

Hi,

First, please, next time post the exact error message. You’ll save
people that want to help you some investigation.

If the folowing message is similar to your error:
W:/var/x.rb:7:in *': can't convert String into Integer (TypeError) from W:/var/x.rb:7:in findroots’
from W:/var/x.rb:21

then you’re trying to multiply numbers by strings.
Replace

    b = (ARGV[0])
    c = (ARGV[1])

by
b = ARGV[0].to_f
c = ARGV[1].to_f
to_f will convert string to float. For more info, read the docs of
String#to_f and possibly the whole String class
(e.g. using RI or RDoc Documentation)

If the message is different, please post it and will see.

Jano

3

Jano S. wrote:

    c = (ARGV[1])

Jano

Hi Thanks for your help and directions. I made the above substitutions
and now I get the following error

% ruby quadratic.rb 1.0 1.0
You entered 1.0 1.0
quadratic.rb:17:in sqrt': Numerical argument out of domain - sqrt (Errno::EDOM) from quadratic.rb:17:infindroots’
from quadratic.rb:30
Here is my program,

#!/usr/bin/env ruby

###########################

program that solve quadratic equation

###########################

class Quadratic

def findroots()
    b = (ARGV[0].to_f)
    c = (ARGV[1].to_f)
    $stdout.print("You entered " , ARGV[1]," ", ARGV[0], "\n")
    discriminant = b * b - 4.0 * c
    sqroot =  Math.sqrt(discriminant)

    root1 = (-b + sqroot) / 2.0
    root2 = (-b - sqroot) / 2.0

    $stdout.print(root1)
    $stdout.print(root2)
end

end

if FILE == $0
qf = Quadratic.new
qf.findroots
end

4

On Mon, Feb 25, 2008 at 3:53 PM, Christian Rubio
[email protected] wrote:

If the message is different, please post it and will see.
(Errno::EDOM)
from quadratic.rb:17:in `findroots’
from quadratic.rb:30

That means you passed a number that has no real square root, for example
-1.
Refresh your high school math and check the discriminant before you
call Math.sqrt :wink:
Otherwise, require ‘complex’ :wink:

Jano

5

Sebastian H. wrote:

HTH,
Sebastian

Thanks all for your replies. The input was invalid. I need to check for
legal input.
But I am new and just learning. Still trying to figure out whats going
on here.
The docs are hard to understand. So I am programming very basically.

Thanks so much
Chris

6

Christian Rubio wrote:

quadratic.rb:17:in sqrt': Numerical argument out of domain - sqrt (Errno::EDOM) from quadratic.rb:17:infindroots’
from quadratic.rb:30

This means that your argument to sqrt is negative.
What values for b and c did you supply?

HTH,
Sebastian