Language: C++

#include<bits/stdc++.h>
#define rep(i,n) for(int i = 0; i<n; i++)
#define ll long long

int main() {
	string s;
	cin >> s;
	vector<int> a(4);
	rep(i,4) a[i] = s[i]-'0';

	for(int bit = 0; bit<(1<<3); bit++){
		string t = to_string(a[0]);
		int sum = a[0];
		for(int i = 0; i<3; i++){
			if(bit&(1<<i)){
				sum+=a[i+1];
				t+=("+" + to_string(a[i+1]));
			}else{
				sum-=a[i+1];
				t+=("-" + to_string(a[i+1]));
			}
		}

		if(sum == 7){
			cout << t << "=7" <<endl;
			return 0;
		}
	}


	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:9: error: 'string' was not declared in this scope
    6 |         string s;
      |         ^~~~~~
a.cc:6:9: note: suggested alternatives:
In file included from /usr/include/c++/14/string:41,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:1:
/usr/include/c++/14/bits/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
/usr/include/c++/14/string:76:11: note:   'std::pmr::string'
   76 |     using string    = basic_string<char>;
      |           ^~~~~~
a.cc:7:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    7 |         cin >> s;
      |         ^~~
      |         std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:7:16: error: 's' was not declared in this scope
    7 |         cin >> s;
      |                ^
a.cc:8:9: error: 'vector' was not declared in this scope
    8 |         vector<int> a(4);
      |         ^~~~~~
a.cc:8:9: note: suggested alternatives:
In file included from /usr/include/c++/14/vector:66,
                 from /usr/include/c++/14/functional:64,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:53:
/usr/include/c++/14/bits/stl_vector.h:428:11: note:   'std::vector'
  428 |     class vector : protected _Vector_base<_Tp, _Alloc>
      |           ^~~~~~
/usr/include/c++/14/vector:93:13: note:   'std::pmr::vector'
   93 |       using vector = std::vector<_Tp, polymorphic_allocator<_Tp>>;
      |             ^~~~~~
a.cc:8:16: error: expected primary-expression before 'int'
    8 |         vector<int> a(4);
      |                ^~~
a.cc:9:18: error: 'a' was not declared in this scope
    9 |         rep(i,4) a[i] = s[i]-'0';
      |                  ^
a.cc:12:23: error: expected ';' before 't'
   12 |                 string t = to_string(a[0]);
      |                       ^~
      |                       ;
a.cc:13:27: error: 'a' was not declared in this scope
   13 |                 int sum = a[0];
      |                           ^
a.cc:17:33: error: 't' was not declared in this scope
   17 |                                 t+=("+" + to_string(a[i+1]));
      |                                 ^
a.cc:17:43: error: 'to_string' was not declared in this scope; did you mean 'std::__cxx11::to_string'?
   17 |                                 t+=("+" + to_string(a[i+1]));
      |                                           ^~~~~~~~~
      |                                           std::__cxx11::to_string
In file included from /usr/include/c++/14/string:54:
/usr/include/c++/14/bits/basic_string.h:4421:3: note: 'std::__cxx11::to_string' declared here
 4421 |   to_string(long double __val)
      |   ^~~~~~~~~
a.cc:20:33: error: 't' was not declared in this scope
   20 |                                 t+=("-" + to_string(a[i+1]));
      |                                 ^
a.cc:20:43: error: 'to_string' was not declared in this scope; did you mean 'std::__cxx11::to_string'?
   20 |                                 t+=("-" + to_string(a[i+1]));
      |                                           ^~~~~~~~~
      |                                           std::__cxx11::to_string
/usr/include/c++/14/bits/basic_string.h:4421:3: note: 'std::__cxx11::to_string' declared here
 4421 |   to_string(long double __val)
      |   ^~~~~~~~~
a.cc:25:25: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   25 |                         cout << t << "=7" <<endl;
      |                         ^~~~
      |                         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:25:33: error: 't' was not declared in this scope; did you mean 'tm'?
   25 |                         cout << t << "=7" <<endl;
      |                                 ^
      |                                 tm
a.cc:25:45: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   25 |                         cout << t << "=7" <<endl;
      |                                             ^~~~
      |                                             std::endl
In file included from /usr/include/c++/14/istream:41,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~