# Program to demonstrate the use of lists to pass changes to parameters
# back to the caller through the argument list
# Matt Bishop, Spring 2014

# this routine tries changes outp
# parameters: inp, a list of one integer
#             outp, a list of one integer
def testparam(inp, outp):
    # announce the values on entry to the function
    print("test begins: inp =", inp[0], "and outp =", outp[0])
    # change the value of the first element of outp
    outp[0] = inp[0] + 10
    # announce the values to see if the change worked
    print("test ends: inp =", inp[0], "and outp =", outp[0])

# call a function that changes parameter values
# and see if the change is reflected in the caller
# calls: testparam
def main():
    # set the values to be used; note these are *lists*
    a = [ 1 ]
    b = [ 2 ]
    # announce the values in the caller, before the call
    print("program begins: a =", a[0], "and b =", b[0])
    # now make the call
    testparam(a, b)
    # announce the values in the caller, after the call
    print("program ends: a =", a[0], "and b =", b[0])

main()