/in/foo.cc: In function 'void exchange(char*, int, char*)':
/in/foo.cc:15:26: warning: unused variable 'count' [-Wunused-variable]
  int i=0, j=0, k=0,mark, count=0;
                          ^~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:50:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(str);
  ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:46,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:50:10: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(str);
          ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:46,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/tmp/ccQihpl7.o: In function `main':
foo.cc:(.text.startup+0x15): warning: the `gets' function is dangerous and should not be used.