/in/foo.cc:20:5: error: 'int index' redeclared as different kind of symbol
 int index=0,low[maxn],num[maxn];
     ^~~~~
In file included from /usr/include/c++/6/cstring:42:0,
                 from /in/foo.cc:4:
/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 tarjan(int, int)':
/in/foo.cc:22:7: error: no post-increment operator for type
  index++;
       ^~
/in/foo.cc:23:20: error: cannot resolve overloaded function 'index' based on conversion to type 'int'
  num[cur]=low[cur]=index;
                    ^~~~~
/in/foo.cc:36:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^