# Test file
# Matt Bishop, February 27, 2012
# ECS 10, Winter Quarter 2012

# function to compute n!
# parameter: n, must be non-negative integer
# returns: n! on success
#          -1 on failure (bad parameter)
def fact(n):
    # check for error in call
    try:
        if n < 0 or n != int(n):
            return -1
    except:
        return -1

    # now compute n! by repeated multiplication
    fact = 1
    for i in range(1, n+1):
        fact *= i
    # return it
    return fact

# Main routine to enable us to test fact()
def main():
    # get the input
    n = int(input("[[WARNING: numbers only! Negative to quit]] n: "))
    # loop until quit
    while n >= 0:
        # say what you got so user can check
        print("%d! = %d" % (n, fact(n)))
        # get another input
        n = int(input("[[WARNING: numbers only! Negative to quit]] n: "))
    # all done! say what user typed
    print("Quitting: n =", n)

main()