As it happens, you don't need to include string.h in item20.cc; it must have been left there from an earlier incarnation of the program that needed that header file. However, to answer your question more generally: string.h and string6.h are different header files that define different structures and functions. Therefore, if you write a program that needs the structures and functions in string.h, you have to include that header, and the same is true for string6.h. Does that answer your question?(posted 9157 days ago)