/in/foo.cc:36:39: error: 'int index' redeclared as different kind of symbol
 int dfn[maxn],low[maxn],instack[maxn],index;
                                       ^~~~~
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 'void tarjan(int)':
/in/foo.cc:41:25: error: no pre-increment operator for type
     dfn[u] = low[u] = ++index;
                         ^~~~~
/in/foo.cc: In function 'void init()':
/in/foo.cc:68:25: error: overloaded function with no contextual type information
     tot = index = scc = 0;
                         ^