C++ - Non-Static Data Member Initializers Only Available With -std=c++11 Or -std=gnu++11

When i define:

int nb_file = 0;

I get an error:

18  16  E:\Ransomware\source\fsociety.h [Warning] non-static data member initializers only available with -std=c++11 or -std=gnu++11

Please check out the picture:

Picture of Error