foo.cc: In function 'int main()':
foo.cc:13:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<ss.size();i++){
              ~^~~~~~~~~~
foo.cc:19:20: error: conversion from 'int' to non-scalar type 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' requested
    string a=ss[i-1]+ss[i];
foo.cc:20:13: error: no match for 'operator-' (operand types are 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' and 'char')
    cout<<t[a-'0'];
            ~^~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/7/bits/char_traits.h:39,
                 from /usr/include/c++/7/ios:40,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/bits/stl_iterator.h:392:5: note: candidate: template<class _IteratorL, class _IteratorR> decltype ((__y.base() - __x.base())) std::operator-(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
     operator-(const reverse_iterator<_IteratorL>& __x,
     ^~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:392:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::reverse_iterator<_Iterator>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/7/bits/char_traits.h:39,
                 from /usr/include/c++/7/ios:40,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/bits/stl_iterator.h:1194:5: note: candidate: template<class _IteratorL, class _IteratorR> decltype ((__x.base() - __y.base())) std::operator-(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)
     operator-(const move_iterator<_IteratorL>& __x,
     ^~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:1194:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::move_iterator<_IteratorL>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/ccomplex:39:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/complex:356:5: note: candidate: template<class _Tp> std::complex<_Tp> std::operator-(const std::complex<_Tp>&, const std::complex<_Tp>&)
     operator-(const complex<_Tp>& __x, const complex<_Tp>& __y)
     ^~~~~~~~
/usr/include/c++/7/complex:356:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::complex<_Tp>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/ccomplex:39:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/complex:365:5: note: candidate: template<class _Tp> std::complex<_Tp> std::operator-(const std::complex<_Tp>&, const _Tp&)
     operator-(const complex<_Tp>& __x, const _Tp& __y)
     ^~~~~~~~
/usr/include/c++/7/complex:365:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::complex<_Tp>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/ccomplex:39:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/complex:374:5: note: candidate: template<class _Tp> std::complex<_Tp> std::operator-(const _Tp&, const std::complex<_Tp>&)
     operator-(const _Tp& __x, const complex<_Tp>& __y)
     ^~~~~~~~
/usr/include/c++/7/complex:374:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   mismatched types 'const std::complex<_Tp>' and 'char'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/ccomplex:39:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/complex:451:5: note: candidate: template<class _Tp> std::complex<_Tp> std::operator-(const std::complex<_Tp>&)
     operator-(const complex<_Tp>& __x)
     ^~~~~~~~
/usr/include/c++/7/complex:451:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::complex<_Tp>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/deque:64:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:68,
                 from foo.cc:1:
/usr/include/c++/7/bits/stl_deque.h:351:5: note: candidate: template<class _Tp, class _Ref, class _Ptr> typename std::_Deque_iterator<_Tp, _Ref, _Ptr>::difference_type std::operator-(const std::_Deque_iterator<_Tp, _Ref, _Ptr>&, const std::_Deque_iterator<_Tp, _Ref, _Ptr>&)
     operator-(const _Deque_iterator<_Tp, _Ref, _Ptr>& __x,
     ^~~~~~~~
/usr/include/c++/7/bits/stl_deque.h:351:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::_Deque_iterator<_Tp, _Ref, _Ptr>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/deque:64:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:68,
                 from foo.cc:1:
/usr/include/c++/7/bits/stl_deque.h:363:5: note: candidate: template<class _Tp, class _RefL, class _PtrL, class _RefR, class _PtrR> typename std::_Deque_iterator<_Tp, _Ref, _Ptr>::difference_type std::operator-(const std::_Deque_iterator<_Tp, _Ref, _Ptr>&, const std::_Deque_iterator<_Tp, _RefR, _PtrR>&)
     operator-(const _Deque_iterator<_Tp, _RefL, _PtrL>& __x,
     ^~~~~~~~
/usr/include/c++/7/bits/stl_deque.h:363:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::_Deque_iterator<_Tp, _Ref, _Ptr>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/vector:65:0,
                 from /usr/include/c++/7/queue:61,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:86,
                 from foo.cc:1:
/usr/include/c++/7/bits/stl_bvector.h:208:3: note: candidate: std::ptrdiff_t std::operator-(const std::_Bit_iterator_base&, const std::_Bit_iterator_base&)
   operator-(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
   ^~~~~~~~
/usr/include/c++/7/bits/stl_bvector.h:208:3: note:   no known conversion for argument 1 from 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' to 'const std::_Bit_iterator_base&'
In file included from /usr/include/c++/7/valarray:592:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95,
                 from foo.cc:1:
/usr/include/c++/7/bits/valarray_after.h:403:5: note: candidate: template<class _Dom1, class _Dom2> std::_Expr<std::_BinClos<std::__minus, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const std::_Expr<_Dom1, typename _Dom1::value_type>&, const std::_Expr<_Dom2, typename _Dom2::value_type>&)
     _DEFINE_EXPR_BINARY_OPERATOR(-, __minus)
     ^
/usr/include/c++/7/bits/valarray_after.h:403:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/valarray:592:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95,
                 from foo.cc:1:
/usr/include/c++/7/bits/valarray_after.h:403:5: note: candidate: template<class _Dom> std::_Expr<std::_BinClos<std::__minus, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const std::_Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)
     _DEFINE_EXPR_BINARY_OPERATOR(-, __minus)
     ^
/usr/include/c++/7/bits/valarray_after.h:403:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/valarray:592:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95,
                 from foo.cc:1:
/usr/include/c++/7/bits/valarray_after.h:403:5: note: candidate: template<class _Dom> std::_Expr<std::_BinClos<std::__minus, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const typename _Dom::value_type&, const std::_Expr<_Dom1, typename _Dom1::value_type>&)
     _DEFINE_EXPR_BINARY_OPERATOR(-, __minus)
     ^
/usr/include/c++/7/bits/valarray_after.h:403:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'char'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/valarray:592:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95,
                 from foo.cc:1:
/usr/include/c++/7/bits/valarray_after.h:403:5: note: candidate: template<class _Dom> std::_Expr<std::_BinClos<std::__minus, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const std::_Expr<_Dom1, typename _Dom1::value_type>&, const std::valarray<typename _Dom::value_type>&)
     _DEFINE_EXPR_BINARY_OPERATOR(-, __minus)
     ^
/usr/include/c++/7/bits/valarray_after.h:403:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/valarray:592:0,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95,
                 from foo.cc:1:
/usr/include/c++/7/bits/valarray_after.h:403:5: note: candidate: template<class _Dom> std::_Expr<std::_BinClos<std::__minus, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const std::valarray<typename _Dom::value_type>&, const std::_Expr<_Dom1, typename _Dom1::value_type>&)
     _DEFINE_EXPR_BINARY_OPERATOR(-, __minus)
     ^
/usr/include/c++/7/bits/valarray_after.h:403:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'char'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95:0,
                 from foo.cc:1:
/usr/include/c++/7/valarray:1173:1: note: candidate: template<class _Tp> std::_Expr<std::_BinClos<std::__minus, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const std::valarray<_Tp>&, const std::valarray<_Tp>&)
 _DEFINE_BINARY_OPERATOR(-, __minus)
 ^
/usr/include/c++/7/valarray:1173:1: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::valarray<_Tp>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95:0,
                 from foo.cc:1:
/usr/include/c++/7/valarray:1173:1: note: candidate: template<class _Tp> std::_Expr<std::_BinClos<std::__minus, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const std::valarray<_Tp>&, const _Tp&)
 _DEFINE_BINARY_OPERATOR(-, __minus)
 ^
/usr/include/c++/7/valarray:1173:1: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::valarray<_Tp>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:95:0,
                 from foo.cc:1:
/usr/include/c++/7/valarray:1173:1: note: candidate: template<class _Tp> std::_Expr<std::_BinClos<std::__minus, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const _Tp&, const std::valarray<_Tp>&)
 _DEFINE_BINARY_OPERATOR(-, __minus)
 ^
/usr/include/c++/7/valarray:1173:1: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   mismatched types 'const std::valarray<_Tp>' and 'char'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/7/bits/char_traits.h:39,
                 from /usr/include/c++/7/ios:40,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/bits/stl_iterator.h:965:5: note: candidate: template<class _Iterator, class _Container> typename __gnu_cxx::__normal_iterator<_Iterator, _Container>::difference_type __gnu_cxx::operator-(const __gnu_cxx::__normal_iterator<_Iterator, _Container>&, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&)
     operator-(const __normal_iterator<_Iterator, _Container>& __lhs,
     ^~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:965:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const __gnu_cxx::__normal_iterator<_Iterator, _Container>'
    cout<<t[a-'0'];
              ^~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/7/bits/char_traits.h:39,
                 from /usr/include/c++/7/ios:40,
                 from /usr/include/c++/7/istream:38,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/bits/stl_iterator.h:953:5: note: candidate: template<class _IteratorL, class _IteratorR, class _Container> decltype ((__lhs.base() - __rhs.base())) __gnu_cxx::operator-(const __gnu_cxx::__normal_iterator<_IteratorL, _Container>&, const __gnu_cxx::__normal_iterator<_IteratorR, _Container>&)
     operator-(const __normal_iterator<_IteratorL, _Container>& __lhs,
     ^~~~~~~~
/usr/include/c++/7/bits/stl_iterator.h:953:5: note:   template argument deduction/substitution failed:
foo.cc:20:14: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const __gnu_cxx::__normal_iterator<_IteratorL, _Container>'
    cout<<t[a-'0'];
              ^~~
foo.cc:26:1: error: expected '}' at end of input
 }
 ^

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