CODEWITHSUNDEEP
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Reputation: 630

Best way to force a user to input an integer in Matlab

I'm writing a simple program in Matlab and am wondering the best way to ensure that the value a user is inputting is a proper integer.

I'm currently using this:

while((num_dice < 1) || isempty(num_dice))
    num_dice = input('Enter the number of dice to roll: ');
end

However I really know there must be a better way, because this doesn't work all the time. I would also like to add error checking ala a try catch block. I'm brand new to Matlab so any input on this would be great.

EDIT2:

try
    while(~isinteger(num_dice) || (num_dice < 1))
        num_dice = sscanf(input('Enter the number of dice to roll: ', 's'), '%d');
    end

    while(~isinteger(faces) || (faces < 1))
        faces = sscanf(input('Enter the number of faces each die has: ', 's'), '%d');
    end

    while(~isinteger(rolls) || (rolls < 1))
        rolls = sscanf(input('Enter the number of trials: ', 's'), '%d');
    end
catch
    disp('Invalid number!')
end

This seems to be working. Is there anything noticeably wrong with this? isinteger is defined by the accepted answer

Upvotes: 5

Views: 22346

Answers (5)

gnovice
gnovice

Reputation: 125874

One easy way to check the properties of function/user-supplied inputs is to use the validateattributes function. I don't know when this function was first introduced; it may not have been present when the question was first asked, but I think it bears mentioning even though the question is older.

If you want to check that a user-supplied input is a scalar, positive, non-zero, real-valued integer of any numeric data type, you can do so using a try-catch block like so:

invalidInput = true;
while invalidInput
  num_dice = input('Enter the number of dice to roll: ');
  try
    validateattributes(num_dice, {'numeric'}, ...
                       {'scalar', 'integer', 'real', 'finite', 'positive'})
    invalidInput = false;
  catch
    disp('Invalid input. Please reenter...');
  end
end

If you're dealing with function inputs instead of a user-supplied input, you could also make use of the inputParser class.

Upvotes: 3

Alp Giray &#214;zen
Alp Giray &#214;zen

Reputation: 1

Try this one. I think it is simpler :)

% Assume false input at the beginning
checkDice = 0;  

% As long as the input is false, stay in the loop
while ~checkDice
    % Take the input as a string
    strDice = input('Enter the number of dice to roll: ', 's');
    % Convert string to number
    dice = str2num(strDice);

    % Length of dice will be 1 iff input is a single number
    if length(dice) ~=1
        checkDice = 0;
    else
        % Search for a positive integer
        checkDice = ((dice>=1) && dice == floor(dice));   
    end

end

Upvotes: -1

b3.
b3.

Reputation: 7175

The following can be used directly in your code and checks against non-integer input including empty, infinite and imaginary values:

isInteger = ~isempty(num_dice) ...
            && isnumeric(num_dice) ...
            && isreal(num_dice) ...
            && isfinite(num_dice) ...
            && (num_dice == fix(num_dice));

The above will only work correctly for scalar input. To test whether a multi-dimensional array contains only integers you can use:

isInteger = ~isempty(x) ...
            && isnumeric(x) ...
            && isreal(x) ...
            && all(isfinite(x)) ...
            && all(x == fix(x))

EDIT

These test for any integer values. To restrict the valid values to positive integers add a num_dice > 0 as in @MajorApus's answer.

You can use the above to force the user to input an integer by looping until they succumb to your demands:

while ~(~isempty(num_dice) ...
            && isnumeric(num_dice) ...
            && isreal(num_dice) ...
            && isfinite(num_dice) ...
            && (num_dice == fix(num_dice)) ...
            && (num_dice > 0))
    num_dice = input('Enter the number of dice to roll: ');
end

Upvotes: 7

Miebster
Miebster

Reputation: 2404

Try this, modify it as needed.

function answer = isint(n)

if size(n) == [1 1]
    answer = isreal(n) && isnumeric(n) && round(n) == n &&  n >0;
else
    answer = false;
end

Upvotes: 6

jonsca
jonsca

Reputation: 10381

Take the input as a string and use sscanf(http://www.mathworks.com/help/techdoc/ref/sscanf.html) to determine if a valid integer was converted from the text.

Upvotes: 0

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