How can I edit my code to produce a function that allows the user to choose the number of 6-sided die they want to roll, and have an optional argument to add them all together? The result should be an array of "rolled" numbers, and the added value.

function Dice = rollDice(rolls,add)
time = clock();
seed = floor(time(end) * 1000);
rng(seed);
number = floor(rand * 6) + 1;
count = 0;

 
 if isempty(rollDice)
     rolls = 2;
 end
 
 if rolls == 0
     msg = 'You didn''t roll any die';
     warning(msg);
 end
Dice = zeros(rolls);
for n = 1:a
count = count + 1;
Dice(n) = number;
end

 if nargin(rollDice) < 2
     add = 0;
else 
add = sum(Dice);
 end
disp(count);
disp(number);

[Caglar]

function [Dice,Sum_of_rolls] = rollDice(rolls,add)
time = clock();
seed = floor(time(end) * 1000);
rng(seed);


for d=rolls:-1:1 %reverse loop to use memory better
    Dice(d)=floor(rand * 6) + 1; %You need to call rand for each roll to get different values.
end

if exist('add','var') %I think checking for the variable instead of nargin is cleaner. You can also add '&& add==1'. 
    Sum_of_rolls=sum(Dice);
else
    Sum_of_rolls=0;
end

end

Answer 1

[Steven Lord]

I have several comments on your code.

function Dice = rollDice(rolls,add)
time = clock();
seed = floor(time(end) * 1000);
rng(seed);

Rather than trying to generate the seed on your own, I would just call rng with the 'shuffle' input.

I would also consider having rollDice accept a third optional input argument. If that input is present, I'd use that in the rng call instead of calling rng('shuffle'). This will allow you to reproduce a set of dice rolls if necessary.

number = floor(rand * 6) + 1;

I recommend using randi instead.

count = 0;
 
 if isempty(rollDice)

There's no variable named rollDice in your function, so this will error. From context I think you're using this to detect if the user called this function with 0 input arguments and rolling a pair of dice in that scenario. If so, I'd use nargin as you did below when you detected whether or not the user had specified the add input argument.

     rolls = 2;
 end
 
 if rolls == 0
     msg = 'You didn''t roll any die';
     warning(msg);
 end
Dice = zeros(rolls);
for n = 1:a
count = count + 1;
Dice(n) = number;

This is the Dilbert random number generator or the xkcd random number generator. This does not call rand or randi each time you refer to number; it instead assigns that same value you generated up above into the element of Dice.

You can also roll all the dice at once. See the "Matrix of Random Numbers" example on the documentation page for the rand function. The "Random Integers" example on that page will also be of interest to you.

end
 if nargin(rollDice) < 2
     add = 0;
else 
add = sum(Dice);
 end
disp(count);
disp(number);

You passed add into the function as an input, but you don't return it from the function as an output. So that variable gets thrown away when your function returns. See this documentation page for an explanation of how to define your function so it returns multiple output arguments.

From a style perspective, I'd also use a different variable name for the input argument that controls "should I return the sum?" and the output argument that contains the sum.

[Terra Gordon]

Thank you for your help. The reason I am seeding like that is because my proffesor requires that method. I have modified the code and now everything works except my optional argument for summing the values rolled together;

function [dice,add] = roll_dice(rolls)

% Random number generator

time = clock(); % Time seeded random number generator

seed = floor(time(end) * 1000);

rng(seed);

%If there are no rolls

if nargin == 0

rolls = 2;

end

array = zeros(1,rolls); % Preallocated array

for n = 1:rolls

number = floor(rand * 6) + 1;

array(n) = number;

end

dice = array; % Store values into an array

if nargin > 1

add = sum(dice);

end

The last if statement is what is causing problems, but I can't think of another solution. Do ypu have any ideas?

[Steven Lord]

Your function is defined to accept at most one input argument, so if nargin > 1 can never be satisfied.

You could use if nargout > 1 to check the number of outputs, or you could compute the sum without checking whether or not the user asked for the second output. If you compute add but the user doesn't call the function with 2 outputs the value assigned to add will be thrown away when the function exits.

If the computation of the add variable was expensive (in terms of memory and/or time) avoiding computing it if it was not asked for could be a good idea, but you'd have to "roll" a lot of dice for that one sum call to be the bottleneck in your code.

[Terra Gordon]

Nargout worked perfectly thank you