new file:   4th/1strrindex.c
	new file:   4th/2itof.c
	deleted:    4th/a.out
	deleted:    4th/calc/a.out
	deleted:    4th/calc/calc.h.gch
	modified:   4th/calc/calc.h
	modified:   4th/calc/getop.c
	modified:   4th/calc/main.c
	modified:   4th/calc/stack.c