The factorial n! of a positive number (integer) is defined by n! = n·(n-1)·(n-2)·. ..· 3·2·1, where 0! = 1. Write a user-defined function that calculates the factorial n! of a number. For function name and arguments, use y=fact (x), where the input argument x is the number whose factorial is to be calculated and the output argument y is the value x!. The function displays an error message if a negative or non-integer number is entered when the function is called. Do not use MATLAB built-in function factorial. Use fact with the following numbers:
(a) 9!
(b) 8.5!
(c) 0!
(d) -5!