Matlab - user input into array

Question

I need to write a program that returns the largest number entered by a user. The user can enter as many numbers >= 0 as they want and when they enter a -1, the program will stop and return the largest number. I am really struggling to do this. So far, I have this:

validInput = false;
while (~validInput)
  fprintf('Enter a number >= 0 or a negative to quit.\n');
  num = input('Enter a number or -1 to quit: ');
  if(num == -1)
    validinput = true;
    counter = 0;
  elseif(num>=0)
    counter = counter+1;
  end;
  if(counter == 0)
    fprintf('No values entered!');
  else
    array = (counter);
     m = max(counter);
     disp(m);
  end
end``

You have validInput and validinput both. Matlab is case sensitive. And there are other problems as well...for instance setting counter to 0 if one enters -1, instead counter should be initialized to 0 before the while loop. And not storing num anywhere, but calling max(counter) for a scalar counter... And that's still not the end of it. — Andras Deak -- Слава Україні
– Andras Deak -- Слава Україні, Commented Sep 24, 2015 at 22:05
Ok I fixed those 2 things, but how do I read numbers greater than or equal to 0 into the array? — William Diuguid
– William Diuguid, Commented Sep 24, 2015 at 22:10
Check out @NKN's solution below. It makes use of the fact that -1<0, so it spares some checks. — Andras Deak -- Слава Україні
– Andras Deak -- Слава Україні, Commented Sep 24, 2015 at 22:11

NKN · Accepted Answer · 2015-09-24 22:10:25Z

1

enteredNumber = 0;
biggestNumber = 0;
while (enteredNumber ~= -1)
    enteredNumber = input('Enter a number : ');
    if enteredNumber > biggestNumber
        biggestNumber = enteredNumber;
    end
end
disp(['The biggest number entered is: ' num2str(biggestNumber)]);

answered Sep 24, 2015 at 22:10

NKN

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Comments

user1543042 · Accepted Answer · 2015-09-24 22:55:01Z

1

You don't need to limit it to positive numbers but to answer your question, you can do this. And remove the || in < 0 to allow the user to choose negative numbers.

num = [];

while (true)
    in = input('Enter a number or a non-numeric character to quit: ');

    if isempty(in) || ~isnumeric(in) || in < 0
        break
    end

    num(end+1) = in;
end

[M, INDEX] = max(num);

if ~isempty(num)
    disp(['The ', num2str(INDEX),' was the maximum entered value and was: ', num2str(M), '.'])
else
    disp('No value entered.')
end

edited Sep 24, 2015 at 22:55

answered Sep 24, 2015 at 22:26

user1543042

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2 Comments

Andras Deak -- Слава Україні Over a year ago

I suggest renaming MAX to something else: a beginner might not realize that the capitalization is intentional, and they might redefine max later in another application.

user1543042 Over a year ago

That's true. I made the change.

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