That's easy:
randi([1,6],1,diceLeft)
generates a 1 x diceLeft matrix of random integer values from the interval [1,6].
For the first call of
dice = [dice randi([1,6],1,diceLeft)];
when dice is empty, you get these diceLeft numbers; for subsequent calls of
dice = [dice randi([1,6],1,diceLeft)];
you add diceLeft new random numbers.
