1. A method of declaring and using variables, the method comprising: determining whether variables are independent variables independently used by a plurality of processors or common variables commonly used by the plurality of processors; declaring the independent variables and storing the independent variables in a plurality of data structures respectively corresponding to the plurality of processors; declaring the common variables and storing the common variables in a shared memory area; allowing each one of the plurality of processors to simultaneously use the independent variables in a corresponding one of the plurality of data structures; and allowing only one of the plurality of processors at a time to use the common variables in the shared memory area.