quickly put/update all variables into/in a structure

default way to do this task is tedious and inflexible
e.g.: s = struct('a',{},'b',{},'c',{})

this simple function can make it better
e.g. s = updateStruct(s, a,b,c)

This function can be used to add/update the existed fields of a structure
OR
directly generate a new structure with given variables as fields.
e.g. s1 = updateStruct( [ ], a,b,c)