Language: C++

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<vector>
#include<string>
#include<sstream>
#include<iomanip>
#include<utility>
#include<cmath>
#include<set>
#include<list>
#include<string>
#include<queue>
#include<stack>
#include<deque>
#include<map>
#include<set>
#include<cstring>
#include<iterator>
#include<bitset>
#include<assert.h>
//#include<chrono>
//#include<time.h>
//#include<windows.h>
using namespace std;
 
//#define int ll
typedef long long ll;
typedef pair<int,int> P;
typedef pair<int,pair<int,int> > PP;
typedef vector<int> VI;
typedef vector<long long int> VL;
//static const int MOD = 1000000007;
//static const int INF = 2147483647;
//static const long long INF = 9223372000000000000;
//static const long long INF = 9223372000000000000/2;
//static const int INF = 1000010000;
//int dx4[4] = {0,1,0,-1}, dy4[4] = {-1,0,1,0};
//int dx5[5] = {-1,0,0,0,1}, dy5[5] = {0,-1,0,1,0};
//int dx8[8] = {-1,0,1,1,1,0,-1,-1}, dy8[8] = {1,1,1,0,-1,-1,-1,0};
//int dx9[9] = {-1,0,1,1,1,0,-1,-1,0}, dy9[9] = {1,1,1,0,-1,-1,-1,0,0};
#define PB push_back
#define MP make_pair
#define MT make_tuple
#define FI first
#define SE second
#define NP next_permutation
#define PQ priority_queue
#define UB upper_bound
#define LB lower_bound
#define SZ(a) int((a).size())
#define LEN(a) int((a).length())
#define SORT(c) sort((c).begin(),(c).end())
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define REP1(i,x) for(int i=1;i<=(int)(x);i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RREP1(i,x) for(int i=((int)(x));i>0;i--)
#define ALL(x) (x).begin(),(x).end()
struct edge {int /*from,*/to,cost;};

main(){
    string s;
    cin >> s;
    string ans;
    REP(i,LEN(s)){
        if(!isdigit(s[i])) ans.erase(LEN(ans)-1,1);
        else ans += s[i];
    }

    cin >> ans << endl;

    return 0;
}


Compiler output:
a.cc:63:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   63 | main(){
      | ^~~~
a.cc: In function 'int main()':
a.cc:72:16: error: no match for 'operator<<' (operand types are 'std::basic_istream<char>' and '<unresolved overloaded function type>')
   72 |     cin >> ans << endl;
      |     ~~~~~~~~~~~^~~~~~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/string_view:763:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, basic_string_view<_CharT, _Traits>)'
  763 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:763:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/bits/basic_string.h:4077:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 4077 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4077:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
In file included from /usr/include/c++/14/bits/memory_resource.h:38,
                 from /usr/include/c++/14/string:68:
/usr/include/c++/14/cstddef:125:5: note: candidate: 'template<class _IntegerType> constexpr std::__byte_op_t<_IntegerType> std::operator<<(byte, _IntegerType)'
  125 |     operator<<(byte __b, _IntegerType __shift) noexcept
      |     ^~~~~~~~
/usr/include/c++/14/cstddef:125:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   couldn't deduce template parameter '_IntegerType'
   72 |     cin >> ans << endl;
      |                   ^~~~
In file included from /usr/include/c++/14/bits/ios_base.h:46:
/usr/include/c++/14/system_error:339:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const error_code&)'
  339 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
      |     ^~~~~~~~
/usr/include/c++/14/system_error:339:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:563:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _CharT)'
  563 |     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:563:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:573:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, char)'
  573 |     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:573:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:579:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, char)'
  579 |     operator<<(basic_ostream<char, _Traits>& __out, char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:579:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<char, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:590:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, signed char)'
  590 |     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:590:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<char, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:595:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, unsigned char)'
  595 |     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:595:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<char, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:654:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const _CharT*)'
  654 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:654:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
In file included from /usr/include/c++/14/ostream:1022:
/usr/include/c++/14/bits/ostream.tcc:307:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const char*)'
  307 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/bits/ostream.tcc:307:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:671:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const char*)'
  671 |     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:671:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<char, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:684:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const signed char*)'
  684 |     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:684:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<char, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:689:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const unsigned char*)'
  689 |     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:689:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<char, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/ostream:810:5: note: candidate: 'template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&)'
  810 |     operator<<(_Ostream&& __os, const _Tp& __x)
      |     ^~~~~~~~
/usr/include/c++/14/ostream:810:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   couldn't deduce template parameter '_Tp'
   72 |     cin >> ans << endl;
      |                   ^~~~
In file included from a.cc:8:
/usr/include/c++/14/iomanip:84:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Resetiosflags)'
   84 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Resetiosflags __f)
      |     ^~~~~~~~
/usr/include/c++/14/iomanip:84:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/iomanip:114:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setiosflags)'
  114 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setiosflags __f)
      |     ^~~~~~~~
/usr/include/c++/14/iomanip:114:5: note:   template argument deduction/substitution failed:
a.cc:72:19: note:   'std::basic_istream<char>' is not derived from 'std::basic_ostream<_CharT, _Traits>'
   72 |     cin >> ans << endl;
      |                   ^~~~
/usr/include/c++/14/iom