A method of declaring and using variables includes; determining whether variables are independent variables or common variables, declaring and storing the independent variables in a plurality of data structures respectively corresponding to the plurality of processors, declaring 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.