
argnum = 0
f0() is called

argnum = 0
NULL for pf is passed to diff_arg() in C

argnum = 1
f1() is called, argl = 10

argnum = 2
f2() is called, arg1 = 10, arg2 = 20

passed varaible number arg
f3() is called, 
arg1 = 0
f3() is called, 
arg1 = 1
arg2 = 20
f3() is called, 
arg1 = 2
arg2 = 20
arg3 = 30.000000
