# This buggy program shows the limitations of parameters.

# Prints a number before and after doubling its value.
def double_number(num):
    print("in double_number, initial value =", num)
    num *= 2
    print("in double_number, final value =", num)

def main():
    x = 17
    double_number(x)
    print("in main, x =", x)
    print()

    num = 42
    double_number(num)
    print("in main, num =", num)

main()