Language: C++

#include<iostream>
#include<string>

int eval(std::stack<std::string> &stc){
    int a, b;
    if(stc.top == "+"){
        stc.pop;
        a = stac.top;
        stc.pop;
        b = stac.top;
        stc.pop;
        return a+b;
    } else if (stc.top == "-") {
        stc.pop;
        a = stc.top;
        stc.pop;
        b = stc.top;
        stc.pop;
        return a-b;
    } else if (stc.top == "*") {
        stc.pop;
        a = stc.top;
        stc.pop;
        b = stc.top;
        stc.pop;
        return a*b;
    }
}


int main(){
    int ans = 0;
    std::string str;
    std::stack<std::string> stc;
    std::cin.tie(0);
    std::ios::sync_with_stdio(false);


    while(std::cin >> str != -1){
       stc.push(str);
       if(stc.top == "+" || stc.top == "-" || stc.top == "*") {
           str = to_string(eval(stc));
           stc.push(str);
       }
    }

    std::cout << stc.top << std::endl;
    return 0;
}

Compiler output:
a.cc:4:15: error: 'stack' is not a member of 'std'
    4 | int eval(std::stack<std::string> &stc){
      |               ^~~~~
a.cc:2:1: note: 'std::stack' is defined in header '<stack>'; this is probably fixable by adding '#include <stack>'
    1 | #include<iostream>
  +++ |+#include <stack>
    2 | #include<string>
a.cc:4:32: error: expected primary-expression before '>' token
    4 | int eval(std::stack<std::string> &stc){
      |                                ^
a.cc:4:35: error: 'stc' was not declared in this scope; did you mean 'std'?
    4 | int eval(std::stack<std::string> &stc){
      |                                   ^~~
      |                                   std
a.cc: In function 'int main()':
a.cc:34:10: error: 'stack' is not a member of 'std'
   34 |     std::stack<std::string> stc;
      |          ^~~~~
a.cc:34:10: note: 'std::stack' is defined in header '<stack>'; this is probably fixable by adding '#include <stack>'
a.cc:34:27: error: expected primary-expression before '>' token
   34 |     std::stack<std::string> stc;
      |                           ^
a.cc:34:29: error: 'stc' was not declared in this scope; did you mean 'str'?
   34 |     std::stack<std::string> stc;
      |                             ^~~
      |                             str
a.cc:39:27: error: no match for 'operator!=' (operand types are 'std::basic_istream<char>' and 'int')
   39 |     while(std::cin >> str != -1){
      |           ~~~~~~~~~~~~~~~ ^~ ~~
      |                    |         |
      |                    |         int
      |                    std::basic_istream<char>
a.cc:39:27: note: candidate: 'operator!=(int, int)' (built-in)
   39 |     while(std::cin >> str != -1){
      |           ~~~~~~~~~~~~~~~~^~~~~
a.cc:39:27: note:   no known conversion for argument 1 from 'std::basic_istream<char>' to 'int'
In file included from /usr/include/c++/14/iosfwd:42,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/postypes.h:197:5: note: candidate: 'template<class _StateT> bool std::operator!=(const fpos<_StateT>&, const fpos<_StateT>&)'
  197 |     operator!=(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:197:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::fpos<_StateT>'
   39 |     while(std::cin >> str != -1){
      |                               ^
In file included from /usr/include/c++/14/string:43,
                 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:
/usr/include/c++/14/bits/allocator.h:243:5: note: candidate: 'template<class _T1, class _T2> bool std::operator!=(const allocator<_CharT>&, const allocator<_T2>&)'
  243 |     operator!=(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:243:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::allocator<_CharT>'
   39 |     while(std::cin >> str != -1){
      |                               ^
In file included from /usr/include/c++/14/string:48:
/usr/include/c++/14/bits/stl_iterator.h:455:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  455 |     operator!=(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:455:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::reverse_iterator<_Iterator>'
   39 |     while(std::cin >> str != -1){
      |                               ^
/usr/include/c++/14/bits/stl_iterator.h:500:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  500 |     operator!=(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::reverse_iterator<_Iterator>'
   39 |     while(std::cin >> str != -1){
      |                               ^
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1686 |     operator!=(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::move_iterator<_IteratorL>'
   39 |     while(std::cin >> str != -1){
      |                               ^
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1753 |     operator!=(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::move_iterator<_IteratorL>'
   39 |     while(std::cin >> str != -1){
      |                               ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/stl_pair.h:1052:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator!=(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1052 |     operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1052:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::pair<_T1, _T2>'
   39 |     while(std::cin >> str != -1){
      |                               ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:651:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  651 |     operator!=(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:651:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   39 |     while(std::cin >> str != -1){
      |                               ^
/usr/include/c++/14/string_view:658:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  658 |     operator!=(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:658:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   39 |     while(std::cin >> str != -1){
      |                               ^
/usr/include/c++/14/string_view:666:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  666 |     operator!=(__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:666:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'int'
   39 |     while(std::cin >> str != -1){
      |                               ^
/usr/include/c++/14/bits/basic_string.h:3833:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3833 |     operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3833:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   39 |     while(std::cin >> str != -1){
      |                               ^
/usr/include/c++/14/bits/basic_string.h:3847:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3847 |     operator!=(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3847:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   mismatched types 'const _CharT*' and 'std::basic_istream<char>'
   39 |     while(std::cin >> str != -1){
      |                               ^
/usr/include/c++/14/bits/basic_string.h:3860:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3860 |     operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3860:5: note:   template argument deduction/substitution failed:
a.cc:39:31: note:   'std::basic_istream<char>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   39 |     while(std::cin >> str != -1){
      |                               ^
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/incl