void function ( ) { }
task 6 : clear and undo clearhistory removes all entries in our history . concode_field_sep PlaceHolder placeHolder concode_field_sep int add concode_elem_sep void printHistory concode_elem_sep void printAllHistory concode_elem_sep int cumulativeSum concode_elem_sep void undoEquation concode_elem_sep int multiply concode_elem_sep void saveEquation concode_elem_sep int cumulativeProduct