/in/foo.cc:12:14: error: 'int index' redeclared as different kind of symbol
 int s,e,temp,index;
              ^~~~~
In file included from /usr/include/c++/7/cstring:42:0,
                 from /in/foo.cc:2:
/usr/include/string.h:477:1: note: previous declaration 'const char* index(const char*, int)'
 index (const char *__s, int __c) __THROW
 ^~~~~
/in/foo.cc: In function 'int ins(int, int)':
/in/foo.cc:44:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'void tarjan(int)':
/in/foo.cc:48:14: error: no pre-increment operator for type
     dfn[x]=++index;
              ^~~~~
/in/foo.cc:49:12: error: cannot resolve overloaded function 'index' based on conversion to type 'int'
     low[x]=index;
            ^~~~~