Should we avoid the old techniques of C++98 or C when we program in this days? [on hold]

Thanks to Stroustrup, C++ is a language 95% compatible with C, in the sense i could write most of my C programs and compile them in a C++ compiler. This is a big feature of C++, and C++ owes a big part of its success tu it, but this has a big desadventage:

Even when in the new C++11 standart we have amazing feature to forget everything about low-level programming, there are a lot of C++ programmers that still use C techniques. Is rare to see someone using smart pointers and other C++ feathures, basically this points:

• There is people that still not even use a single feature or C++11 (not talking about C++14 & C++17).
• There is people that still use the C-style stings and "string.h"
• People that use "header.h" instead of < cheader >
• People that write C programs, compile it in a C++ compiler, and say they now C++ (the worst ones).

My question as a new C++ programmer that loves the language: Should we disapprove the use of old techniques in C++ programming and use the new ones? Should we forget everything about C and C++98? Or we should continue doing a mix of both everytime we see it convenient