Language: C++

#include <stdio.h>
#include<iostream>
#include <string>

int main(){
  std::string a;
  std::string s;
  int ad;
  std::cin >> a;
  if(a == "SUN"){
    s == "日曜日";
    ad == 7;
  }
  else if(a=="MON"){
    s == "月曜日";
    ad == 6;
  }
  else if(a=="TUE"){
    s == "火曜日";
    ad == 5;
  }
  else if(a=="WED"){
    s == "水曜日";
    ad == 4;
  }
  else if(a=="THU"){
    s == "木曜日";
    ad == 3;
  }
  else if(a=="FRI"){
    s == "金曜日";
    ad == 2;
  }
  else if(a=="SAT"){
    s == "土曜日";
    ad == 1;
  }
  std::string s1("今日は");
  std::string s2("です。よって、次の日曜日は");
  std::string s3("日後です。");
  std::string s4 = s1 + s + s2 + ad + s3;
  std::cout <<  s4 << std::endl;
}



Compiler output:
a.cc: In function 'int main()':
a.cc:11:7: warning: ignoring return value of 'bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*) [with _CharT = char; _Traits = char_traits<char>; _Alloc = allocator<char>]', declared with attribute 'nodiscard' [-Wunused-result]
   11 |     s == "日曜日";
      |     ~~^~~~~~~~~~~
In file included 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:2:
/usr/include/c++/14/bits/basic_string.h:3772:5: note: declared here
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
a.cc:15:7: warning: ignoring return value of 'bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*) [with _CharT = char; _Traits = char_traits<char>; _Alloc = allocator<char>]', declared with attribute 'nodiscard' [-Wunused-result]
   15 |     s == "月曜日";
      |     ~~^~~~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note: declared here
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
a.cc:19:7: warning: ignoring return value of 'bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*) [with _CharT = char; _Traits = char_traits<char>; _Alloc = allocator<char>]', declared with attribute 'nodiscard' [-Wunused-result]
   19 |     s == "火曜日";
      |     ~~^~~~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note: declared here
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
a.cc:23:7: warning: ignoring return value of 'bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*) [with _CharT = char; _Traits = char_traits<char>; _Alloc = allocator<char>]', declared with attribute 'nodiscard' [-Wunused-result]
   23 |     s == "水曜日";
      |     ~~^~~~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note: declared here
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
a.cc:27:7: warning: ignoring return value of 'bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*) [with _CharT = char; _Traits = char_traits<char>; _Alloc = allocator<char>]', declared with attribute 'nodiscard' [-Wunused-result]
   27 |     s == "木曜日";
      |     ~~^~~~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note: declared here
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
a.cc:31:7: warning: ignoring return value of 'bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*) [with _CharT = char; _Traits = char_traits<char>; _Alloc = allocator<char>]', declared with attribute 'nodiscard' [-Wunused-result]
   31 |     s == "金曜日";
      |     ~~^~~~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note: declared here
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
a.cc:35:7: warning: ignoring return value of 'bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*) [with _CharT = char; _Traits = char_traits<char>; _Alloc = allocator<char>]', declared with attribute 'nodiscard' [-Wunused-result]
   35 |     s == "土曜日";
      |     ~~^~~~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note: declared here
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
a.cc:41:32: error: no match for 'operator+' (operand types are 'std::__cxx11::basic_string<char>' and 'int')
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                    ~~~~~~~~~~~ ^ ~~
      |                           |      |
      |                           |      int
      |                           std::__cxx11::basic_string<char>
In file included from /usr/include/c++/14/string:48:
/usr/include/c++/14/bits/stl_iterator.h:627:5: note: candidate: 'template<class _Iterator> constexpr std::reverse_iterator<_Iterator> std::operator+(typename reverse_iterator<_Iterator>::difference_type, const reverse_iterator<_Iterator>&)'
  627 |     operator+(typename reverse_iterator<_Iterator>::difference_type __n,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:627:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and 'int'
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/stl_iterator.h:1798:5: note: candidate: 'template<class _Iterator> constexpr std::move_iterator<_IteratorL> std::operator+(typename move_iterator<_IteratorL>::difference_type, const move_iterator<_IteratorL>&)'
 1798 |     operator+(typename move_iterator<_Iterator>::difference_type __n,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1798:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   mismatched types 'const std::move_iterator<_IteratorL>' and 'int'
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/basic_string.h:3598:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3598 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3598:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/basic_string.h:3616:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3616 |     operator+(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3616:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   mismatched types 'const _CharT*' and 'std::__cxx11::basic_string<char>'
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/basic_string.h:3635:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(_CharT, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3635 |     operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3635:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/basic_string.h:3652:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3652 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3652:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   mismatched types 'const _CharT*' and 'int'
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/basic_string.h:3670:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, _CharT)'
 3670 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, _CharT __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3670:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   deduced conflicting types for parameter '_CharT' ('char' and 'int')
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/basic_string.h:3682:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3682 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3682:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/basic_string.h:3689:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3689 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3689:5: note:   template argument deduction/substitution failed:
a.cc:41:34: note:   mismatched types 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   41 |   std::string s4 = s1 + s + s2 + ad + s3;
      |                                  ^~
/usr/include/c++/14/bits/basic_string.h:3