Question

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

Answer 1

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