Language: C++

#include <bits/stdc++.h>

using namespace std;

int main(){
    ios_base::sync_with_stdio (false);
    string s[30],ans;
    cin>>s;
    int l=s.size(),a[26]={0},i,p;
    for(i=0;i<l;i++){
        a[int(s[i])-97]++;
    }
    for(i=0;i<26;i++)
        if(a[i]==0) {p=i;
        break;
        }
    if(l<26){
        for(i=0;i<l;i++){
            ans[i]=s[i];
        }
        ans[l]=char(p+97);
        cout<<ans;
        return 0;
    }
    else cout<<-1;
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:8:8: error: no match for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'std::string [30]' {aka 'std::__cxx11::basic_string<char> [30]'})
    8 |     cin>>s;
      |     ~~~^~~
      |     |    |
      |     |    std::string [30] {aka std::__cxx11::basic_string<char> [30]}
      |     std::istream {aka std::basic_istream<char>}
In file included from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127,
                 from a.cc:1:
/usr/include/c++/14/istream:170:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  170 |       operator>>(bool& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:170:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: cannot bind non-const lvalue reference of type 'bool&' to a value of type 'std::string*' {aka 'std::__cxx11::basic_string<char>*'}
    8 |     cin>>s;
      |          ^
/usr/include/c++/14/istream:174:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  174 |       operator>>(short& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:174:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'short int' [-fpermissive]
    8 |     cin>>s;
      |          ^
      |          |
      |          std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:8:10: error: cannot bind rvalue '(short int)((std::string*)(& s))' to 'short int&'
/usr/include/c++/14/istream:177:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  177 |       operator>>(unsigned short& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:177:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'short unsigned int' [-fpermissive]
    8 |     cin>>s;
      |          ^
      |          |
      |          std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:8:10: error: cannot bind rvalue '(short unsigned int)((std::string*)(& s))' to 'short unsigned int&'
/usr/include/c++/14/istream:181:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  181 |       operator>>(int& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:181:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'int' [-fpermissive]
    8 |     cin>>s;
      |          ^
      |          |
      |          std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:8:10: error: cannot bind rvalue '(int)((std::string*)(& s))' to 'int&'
/usr/include/c++/14/istream:184:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  184 |       operator>>(unsigned int& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:184:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'unsigned int' [-fpermissive]
    8 |     cin>>s;
      |          ^
      |          |
      |          std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:8:10: error: cannot bind rvalue '(unsigned int)((std::string*)(& s))' to 'unsigned int&'
/usr/include/c++/14/istream:188:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  188 |       operator>>(long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:188:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'long int' [-fpermissive]
    8 |     cin>>s;
      |          ^
      |          |
      |          std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:8:10: error: cannot bind rvalue '(long int)((std::string*)(& s))' to 'long int&'
/usr/include/c++/14/istream:192:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  192 |       operator>>(unsigned long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:192:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'long unsigned int' [-fpermissive]
    8 |     cin>>s;
      |          ^
      |          |
      |          std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:8:10: error: cannot bind rvalue '(long unsigned int)((std::string*)(& s))' to 'long unsigned int&'
/usr/include/c++/14/istream:199:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  199 |       operator>>(long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:199:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'long long int' [-fpermissive]
    8 |     cin>>s;
      |          ^
      |          |
      |          std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:8:10: error: cannot bind rvalue '(long long int)((std::string*)(& s))' to 'long long int&'
/usr/include/c++/14/istream:203:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  203 |       operator>>(unsigned long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:203:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'long long unsigned int' [-fpermissive]
    8 |     cin>>s;
      |          ^
      |          |
      |          std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:8:10: error: cannot bind rvalue '(long long unsigned int)((std::string*)(& s))' to 'long long unsigned int&'
/usr/include/c++/14/istream:328:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  328 |       operator>>(void*& __p)
      |       ^~~~~~~~
/usr/include/c++/14/istream:328:7: note:   conversion of argument 1 would be ill-formed:
a.cc:8:10: error: cannot bind non-const lvalue reference of type 'void*&' to an rvalue of type 'void*'
    8 |     cin>>s;
      |          ^
/usr/include/c++/14/istream:219:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]'
  219 |       operator>>(float& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:219:25: note:   no known conversion for argument 1 from 'std::string [30]' {aka 'std::__cxx11::basic_string<char> [30]'} to 'float&'
  219 |       operator>>(float& __f)
      |                  ~~~~~~~^~~
/usr/include/c++/14/istream:223:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]'
  223 |       operator>>(double& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:223:26: note:   no known conversion for argument 1 from 'std::string [30]' {aka 'std::__cxx11::basic_string<char> [30]'} to 'double&'
  223 |       operator>>(double& __f)
      |                  ~~~~~~~~^~~
/usr/include/c++/14/istream:227:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]'
  227 |       operator>>(long double& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:227:31: note:   no known conversion for argument 1 from 'std::string [30]' {aka 'std::__cxx11::basic_string<char> [30]'} to 'long double&'
  227 |       operator>>(long double& __f)
      |                  ~~~~~~~~~~~~~^~~
/usr/include/c++/14/istream:122:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__istream_type& (*)(__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]'
  122 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:122:36: note:   no known conversion for argument 1 from 'std::str