/in/foo.cc:6:11: error: 'int index' redeclared as different kind of symbol
 int top=0,index=0,tot=0,num=0,asd=0;
           ^~~~~
In file included from /usr/include/c++/6/cstring:42:0,
                 from /in/foo.cc:3:
/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:24:18: error: no pre-increment operator for type
  dfn[x]=low[x]=++index;
                  ^~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:49:8: warning: unused variable 'm' [-Wunused-variable]
  int n,m;
        ^
/in/foo.cc:51:8: warning: unused variable 'w' [-Wunused-variable]
  int q,w;
        ^