Language: C++

//(・ω・)
#include <iostream> // cout, endl, cin
#include <string> // string, to_string, atoi
#include <vector> // vector
#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility> // pair, make_pair
#include <tuple> // tuple, make_tuple
#include <cstdint> // int64_t, int*_t
#include <cstdio> // printf
#include <map> // map
#include <queue> // queue, priority_queue
#include <set> // set
#include <stack> // stack
#include <deque> // deque
#include <unordered_map> // unordered_map
#include <unordered_set> // unordered_set
#include <bitset> // bitset
#include <cctype> // isupper, islower, isdigit, toupper, tolower
#include <math.h>
#include <iomanip> //setprecision
#include <limits>
#include <sstream> //istringstream
using namespace std;

int main(){
  string s,t,u;
  int a,b;
  cin >> s >> t >> a >> b >> u;
  if(a==b){
      cout << s-1 << t << endl;
  }
  else{
      cout << s << t-1 << endl;
  }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:30:16: error: no match for 'operator-' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'int')
   30 |       cout << s-1 << t << endl;
      |               ~^~
      |               | |
      |               | int
      |               std::string {aka std::__cxx11::basic_string<char>}
In file included from /usr/include/c++/14/string:48,
                 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/stl_iterator.h:618:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  618 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:618:5: note:   template argument deduction/substitution failed:
a.cc:30:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   30 |       cout << s-1 << t << endl;
      |                 ^
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1790 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note:   template argument deduction/substitution failed:
a.cc:30:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   30 |       cout << s-1 << t << endl;
      |                 ^
a.cc:33:21: error: no match for 'operator-' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'int')
   33 |       cout << s << t-1 << endl;
      |                    ~^~
      |                    | |
      |                    | int
      |                    std::string {aka std::__cxx11::basic_string<char>}
/usr/include/c++/14/bits/stl_iterator.h:618:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  618 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:618:5: note:   template argument deduction/substitution failed:
a.cc:33:22: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   33 |       cout << s << t-1 << endl;
      |                      ^
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1790 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note:   template argument deduction/substitution failed:
a.cc:33:22: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   33 |       cout << s << t-1 << endl;
      |                      ^