Can anybody spot the error in this simple program?

Hey, this is probably going to be very obvious to you guys, but I have written this program to assign grades to students marks, and I can't seem to spot the error, it always seems to give me 'fail' and just keeps repeating fail over and over again!

score = input('What did the pupil score?');
while 100>= score >= 0
    if 40>score>=0 
        disp('Fail');
    end
    if 50>score>=40 
        disp('Third');
    end

      if 70>score>=50 
          disp('Second');
      end

      if 100>=score>70; 
          disp('First'); 
      end;
  end;

Thank you in advance!

[Daniel Shub]

I always go to http://matlab.wikia.com/wiki/FAQ looking for this question. It surprises me that it is not an FAQ yet.

Answer 1

[Daniel Shub]

This 100>= score >= 0 doesn't do what you think it does.

100>= score

either evaluates to 0 or 1, so you then compare

0>=0

or

1>=0

which are both true.

Answer 2

[Wayne King]

Daniel's absolutely correct. You're writing your inequalities like you would write them on a piece of paper, but MATLAB is a programming language

score = 0;
while (score>=0 && score <= 100)

score = input('What did the pupil score?\n');

      if (40>score && score>=0) 
          disp('Fail');
      end
      if (50>score && score >=40 )
          disp('Third');
      end
        if (70>score && score>=50) 
            disp('Second');
        end
        if (100>=score && score>=70)
            disp('First'); 
        end;
    end;

[Eike]

Since the time of my first C programs I'm waiting for the programming language that allows me to write my inequalities like Edward did... I mean how often do you come across such situations?

Anybody knows a language owning that feature? :)

Answer 3

[Edward]

That's great thanks guys! If I knew how to, or could, I would give you rep!

[Daniel Shub]

It is easy. Click the triangle next to "0 votes" to upvote and click the big box "accept answer" for the answer that answers your question.