Language: C++

#include<iostream>
#include<string>
#include<cstdio>

using namespace std;

int main(){

	string str;
	cin >> str;
	bool alp[26];
	for(int i=0;i<26;i++){
		alp[i]=false;
	}
	for(int i=0;i<str.size();i++){
		alp[str[i]-'a']=true;
	}
	for(int i=0;i<26;i++){
		if(!alp[i]){
			cout << (char)('a'+i) << endl;
			return 0;
		}
	}
cout >> "None" >> endl;
return 0;

}

Compiler output:
a.cc: In function 'int main()':
a.cc:24:6: error: no match for 'operator>>' (operand types are 'std::ostream' {aka 'std::basic_ostream<char>'} and 'const char [5]')
   24 | cout >> "None" >> endl;
      | ~~~~ ^~ ~~~~~~
      | |       |
      | |       const char [5]
      | std::ostream {aka std::basic_ostream<char>}
In file included from /usr/include/c++/14/string:55,
                 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/bits/basic_string.tcc:835:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
  835 |     operator>>(basic_istream<_CharT, _Traits>& __in,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.tcc:835:5: note:   template argument deduction/substitution failed:
a.cc:24:9: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'std::basic_istream<_CharT, _Traits>'
   24 | cout >> "None" >> 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:131:5: note: candidate: 'template<class _IntegerType> constexpr std::__byte_op_t<_IntegerType> std::operator>>(byte, _IntegerType)'
  131 |     operator>>(byte __b, _IntegerType __shift) noexcept
      |     ^~~~~~~~
/usr/include/c++/14/cstddef:131:5: note:   template argument deduction/substitution failed:
a.cc:24:1: note:   cannot convert 'std::cout' (type 'std::ostream' {aka 'std::basic_ostream<char>'}) to type 'std::byte'
   24 | cout >> "None" >> endl;
      | ^~~~
In file included from /usr/include/c++/14/istream:1109,
                 from /usr/include/c++/14/iostream:42:
/usr/include/c++/14/bits/istream.tcc:978:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _CharT&)'
  978 |     operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c)
      |     ^~~~~~~~
/usr/include/c++/14/bits/istream.tcc:978:5: note:   template argument deduction/substitution failed:
a.cc:24:9: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'std::basic_istream<_CharT, _Traits>'
   24 | cout >> "None" >> endl;
      |         ^~~~~~
/usr/include/c++/14/istream:849:5: note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(basic_istream<char, _Traits>&, unsigned char&)'
  849 |     operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
      |     ^~~~~~~~
/usr/include/c++/14/istream:849:5: note:   template argument deduction/substitution failed:
a.cc:24:9: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'std::basic_istream<char, _Traits>'
   24 | cout >> "None" >> endl;
      |         ^~~~~~
/usr/include/c++/14/istream:854:5: note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(basic_istream<char, _Traits>&, signed char&)'
  854 |     operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
      |     ^~~~~~~~
/usr/include/c++/14/istream:854:5: note:   template argument deduction/substitution failed:
a.cc:24:9: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'std::basic_istream<char, _Traits>'
   24 | cout >> "None" >> endl;
      |         ^~~~~~
/usr/include/c++/14/istream:896:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(basic_istream<_CharT, _Traits>&, _CharT*)'
  896 |     operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s)
      |     ^~~~~~~~
/usr/include/c++/14/istream:896:5: note:   template argument deduction/substitution failed:
a.cc:24:9: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'std::basic_istream<_CharT, _Traits>'
   24 | cout >> "None" >> endl;
      |         ^~~~~~
/usr/include/c++/14/istream:939:5: note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(basic_istream<char, _Traits>&, unsigned char*)'
  939 |     operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/istream:939:5: note:   template argument deduction/substitution failed:
a.cc:24:9: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'std::basic_istream<char, _Traits>'
   24 | cout >> "None" >> endl;
      |         ^~~~~~
/usr/include/c++/14/istream:945:5: note: candidate: 'template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(basic_istream<char, _Traits>&, signed char*)'
  945 |     operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
      |     ^~~~~~~~
/usr/include/c++/14/istream:945:5: note:   template argument deduction/substitution failed:
a.cc:24:9: note:   'std::ostream' {aka 'std::basic_ostream<char>'} is not derived from 'std::basic_istream<char, _Traits>'
   24 | cout >> "None" >> endl;
      |         ^~~~~~
/usr/include/c++/14/istream:1099:5: note: candidate: 'template<class _Istream, class _Tp> _Istream&& std::operator>>(_Istream&&, _Tp&&)'
 1099 |     operator>>(_Istream&& __is, _Tp&& __x)
      |     ^~~~~~~~
/usr/include/c++/14/istream:1099:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/istream: In substitution of 'template<class _Istream, class _Tp> _Istream&& std::operator>>(_Istream&&, _Tp&&) [with _Istream = std::basic_ostream<char>&; _Tp = const char (&)[5]]':
a.cc:24:9:   required from here
   24 | cout >> "None" >> endl;
      |         ^~~~~~
/usr/include/c++/14/istream:1099:5: error: no type named 'type' in 'struct std::enable_if<false, void>'
 1099 |     operator>>(_Istream&& __is, _Tp&& __x)
      |     ^~~~~~~~