Language: C++

# include<iostream>
using namespace std;
int main() {
    string str[];
    char ch;
    while (cin >> str) {
        for (int i=0;i<str.size();i++) {
            ch = str[i];
            if (isalpha(ch)) {
                if (isupper(ch)) {
                    ch = tolower(ch);
                } else {
                    ch = toupper(ch);
                }
                cout << ch;
            } else {
                cout << ch;
            }
        }
        if (ch != '.') {
            cout << " ";
        }
    }
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:4:12: error: array size missing in 'str'
    4 |     string str[];
      |            ^~~
a.cc:6:16: error: no match for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'std::string [1]' {aka 'std::__cxx11::basic_string<char> [1]'})
    6 |     while (cin >> str) {
      |            ~~~ ^~ ~~~
      |            |      |
      |            |      std::string [1] {aka std::__cxx11::basic_string<char> [1]}
      |            std::istream {aka std::basic_istream<char>}
In file included from /usr/include/c++/14/iostream:42,
                 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:6:19: error: cannot bind non-const lvalue reference of type 'bool&' to a value of type 'std::string*' {aka 'std::__cxx11::basic_string<char>*'}
    6 |     while (cin >> str) {
      |                   ^~~
/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:6:19: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'short int' [-fpermissive]
    6 |     while (cin >> str) {
      |                   ^~~
      |                   |
      |                   std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:6:19: error: cannot bind rvalue '(short int)((std::string*)(& str))' 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:6:19: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'short unsigned int' [-fpermissive]
    6 |     while (cin >> str) {
      |                   ^~~
      |                   |
      |                   std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:6:19: error: cannot bind rvalue '(short unsigned int)((std::string*)(& str))' 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:6:19: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'int' [-fpermissive]
    6 |     while (cin >> str) {
      |                   ^~~
      |                   |
      |                   std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:6:19: error: cannot bind rvalue '(int)((std::string*)(& str))' 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:6:19: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'unsigned int' [-fpermissive]
    6 |     while (cin >> str) {
      |                   ^~~
      |                   |
      |                   std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:6:19: error: cannot bind rvalue '(unsigned int)((std::string*)(& str))' 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:6:19: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'long int' [-fpermissive]
    6 |     while (cin >> str) {
      |                   ^~~
      |                   |
      |                   std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:6:19: error: cannot bind rvalue '(long int)((std::string*)(& str))' 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:6:19: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'long unsigned int' [-fpermissive]
    6 |     while (cin >> str) {
      |                   ^~~
      |                   |
      |                   std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:6:19: error: cannot bind rvalue '(long unsigned int)((std::string*)(& str))' 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:6:19: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'long long int' [-fpermissive]
    6 |     while (cin >> str) {
      |                   ^~~
      |                   |
      |                   std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:6:19: error: cannot bind rvalue '(long long int)((std::string*)(& str))' 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:6:19: error: invalid conversion from 'std::string*' {aka 'std::__cxx11::basic_string<char>*'} to 'long long unsigned int' [-fpermissive]
    6 |     while (cin >> str) {
      |                   ^~~
      |                   |
      |                   std::string* {aka std::__cxx11::basic_string<char>*}
a.cc:6:19: error: cannot bind rvalue '(long long unsigned int)((std::string*)(& str))' 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:6:19: error: cannot bind non-const lvalue reference of type 'void*&' to an rvalue of type 'void*'
    6 |     while (cin >> str) {
      |                   ^~~
/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 [1]' {aka 'std::__cxx11::basic_string<char> [1]'} 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 [1]' {aka 'std::__cxx11::basic_string<char> [1]'} 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 [1]' {aka 'std::__cxx11::basic_string<char> [1]'} 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<