My program to calculate roots works incorrectly?

I have the user input a, b, and c (of a quadratic equation) into a dialog box. the discriminate is calculated and if it's greater than 0, it should output "two roots", less than 0 "no roots", etc. However, everything I enter returns "no roots"

prompt={'enter a: ','Enter b: ','Enter c: '};

dlg_title='quadratic';

answer=inputdlg(prompt,dlg_title);

a = (answer{1});

b = (answer{2});

c = (answer{3});

D = b^2 - 4.*a.*c;

p = [a b c];

if D>0

    disp('There are two roots')

    r = roots(p)

elseif D<0

    disp('There are no roots')

else

    disp('There is one root')

    r = roots(p)

end

any ideas how to fix it? I'm not very experience with matlab so I'm sure what I've done wrong.

Answer 1

[Star Strider]

Your ‘answer’ variable is a cell array of strings. You have to liberate the numbers from their string representation:

a = str2num(answer{1});
b = str2num(answer{2});
c = str2num(answer{3});

[Elise M.]

I just tried that and it still isn't working :/

[Star Strider]

It works perfectly for me with the addition of str2num.

Example:

answer = [1,2,1]

There is one root

r =

      -1.0000e+000
      -1.0000e+000

answer = [1,3,2]

There are two roots

r =

      -2.0000e+000
      -1.0000e+000

answer = [1,2,3]

There are no roots

Enter the values for ‘answer’ in the input dialogue and you should get the same results as I did.

[Elise M.]

Okay I made a change that I forgot to switch back before I tried and those worked for mine too, thank you!!

[Star Strider]

My pleasure!

Say ‘Hi!’ to Kayla for me, too!

[Elise M.]

who?

[Star Strider]

Someone who seemed to be working on exactly the same problem as you were. Thought you might have been classmates.