#include<string.h>
#include<cstring>
what is the difference?
One is a C header, from the C programming language. It is a set of functions for working with character arrays.
One is the C++ provided header to allow people who simply must use those C functions to use them, with some improvements in the code.
Stop asking the same basic question in different threads. You're asking "What's the difference between C headers and C++ headers?"