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. Use fact with the following numbers: 12! 0! -7! 6.7!