/in/foo.cc: In function 'int main()':
/in/foo.cc:51:9: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
         gets(str);
         ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 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:51:17: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
         gets(str);
                 ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 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:54:29: error: 'isalnum' was not declared in this scope
         while(isalnum(str[j])) {
                             ^
/in/foo.cc:63:33: error: 'isalnum' was not declared in this scope
             while(isalnum(str[j])) {
                                 ^