''' Purpose: try out functions
'''
import harb                             # import access to module harb

# import statements are necessary to access functions beyond the built-in
# we've imported url and random in the past, now we'll write our own modules and import those
# just like with url.py, we must have our module files in the same folder as our programs
# if you have organization issues in pycharm please see a TA!

n1, n2 =  3, 14                         # get some values for function exploration
n3, n4 = 15, 92
n5, n6 = -6, 53

t1 = harb.add( n1, n2 )                 # invoke harb.add() with arguments n1 and n2
                                        # return value used to set t1

# these are function invokations, we grab out the add() function from the harb.py module
# when the add() function is running, it needs to be flexible. it cannot count on n1 being the same every time
# we need to know how many pieces of information we're being given and how to use them
# using a function v. making a function
    # using -> invoking -> give arguments in the parentheses (add takes two arguments in each invokation)
        # a copy of those arguments are handed into the function
        # the function does not know the memory locations of the arguments and cannot change them
        # this differs from language to language
        # arguments could be numbers, strings, variables, literals, functions
            # if we handed 2 strings to the harb.add() function, it would concatenate them
    # making -> defining -> set up with parameters: special variables that are initialized when function is invoked
        # parameters are similar to loop variables, they are stand ins for the arguments that are later passed in
# when we call a function, we run the code of the function ( ex. harb.add( n1, n2 ) )
# we leave the original program and go to the add() function, it has control over the program flow
# while the function is in charge, we can access variables from harb.py, but not the variables in inger.py
# copies of n1 and n2 are passed into the function, the function returns
# the main code is paused until we reach a return value, then
t2 = harb.add( n3, n4 )                 # invoke harb.add() with arguments n3 and n4
                                        # return value used to set t2

# we have to hand add() exactly two things (or arguments) or it will get mad at us
# all functions do something, but not all functions hand something back ( think print() and append() )
# "handing back" is returning in python. this is not the same as using print()
    # print() displays output
    # returning hands back relevant information to the program that called (or invoked) the function
# when you write functions in CS 1112, you might return every time, but you will NOT use print() statements in functions
# printing is for the user, returning is for the code. we want to capture the output and use it, so we return

# a function will do the same thing every run

print( "add(", n1, ",", n2, "):", t1 )  # print first  add() result
print( "add(", n3, ",", n4, "):", t2 )  # print second add() result

print()

i1 = harb.negate( n5 )                  # invoke harb.negate() with argument n5
                                        # return value used to set i1

i2 = harb.negate( n6 )                  # invoke harb.negate() with argument n6
                                        # return value used to set i2

print( "inverse(", n5, "):", i1 )       # print first  inverse() result
print( "inverse(", n6, "):", i2 )       # print second inverse() result