/in/foo.cc: In function 'int main()':
/in/foo.cc:14:18: error: invalid conversion from 'const char*' to 'char*' [-fpermissive]
   sprintf(s.c_str(),"%d",i);
           ~~~~~~~^~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/c++/6/ext/string_conversions.h:43,
                 from /usr/include/c++/6/bits/basic_string.h:5417,
                 from /usr/include/c++/6/string:52,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/stdio.h:366:12: note:   initializing argument 1 of 'int sprintf(char*, const char*, ...)'
 extern int sprintf (char *__restrict __s,
            ^~~~~~~