Language: C++

#include <cstdio>
#include <stack>

int main() {
  int total_area = 0;

  stack<int> s1;
  stack<pair<int, int>> s2;

  char c;
  int i = 0;
  for (scanf("%c", &c); c != '\n'; scanf("%c", &c), ++i) {
    switch(c) {
      case '\\':
        s1.push(i);
        break;
      case '_':
        break;
      case '/':
        if (s1.empty()) break;
        ip = s1.top();
        s1.pop();
        area = ip - i;
        total_area += area;
        while (s2.empty == false && s2.top().first > ip) {
          area += s2.top().second;
          s2.pop();
        }
        s2.push(make_pair(ip, area));
        break;
    }
  }

  s = s2.size();
  int a[s];
  for (int i = s - 1; i >= 0; --i) {
    a[i] = s2.top().second;
    s2.pop();
  }

  printf("%d\n", total_area);
  printf("%d", s);
  for (int i = 0; i < s; ++i)
    printf(" %d", a[i]);
  printf("\n");

  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:3: error: 'stack' was not declared in this scope; did you mean 'std::stack'?
    7 |   stack<int> s1;
      |   ^~~~~
      |   std::stack
In file included from /usr/include/c++/14/stack:63,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_stack.h:99:11: note: 'std::stack' declared here
   99 |     class stack
      |           ^~~~~
a.cc:7:9: error: expected primary-expression before 'int'
    7 |   stack<int> s1;
      |         ^~~
a.cc:8:9: error: 'pair' was not declared in this scope; did you mean 'std::pair'?
    8 |   stack<pair<int, int>> s2;
      |         ^~~~
      |         std::pair
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/deque:62,
                 from /usr/include/c++/14/stack:62:
/usr/include/c++/14/bits/stl_pair.h:89:12: note: 'std::pair' declared here
   89 |     struct pair;
      |            ^~~~
a.cc:8:14: error: expected primary-expression before 'int'
    8 |   stack<pair<int, int>> s2;
      |              ^~~
a.cc:15:9: error: 's1' was not declared in this scope
   15 |         s1.push(i);
      |         ^~
a.cc:21:9: error: 'ip' was not declared in this scope; did you mean 'i'?
   21 |         ip = s1.top();
      |         ^~
      |         i
a.cc:23:9: error: 'area' was not declared in this scope
   23 |         area = ip - i;
      |         ^~~~
a.cc:25:16: error: 's2' was not declared in this scope
   25 |         while (s2.empty == false && s2.top().first > ip) {
      |                ^~
a.cc:29:9: error: 's2' was not declared in this scope
   29 |         s2.push(make_pair(ip, area));
      |         ^~
a.cc:29:17: error: 'make_pair' was not declared in this scope; did you mean 'std::make_pair'?
   29 |         s2.push(make_pair(ip, area));
      |                 ^~~~~~~~~
      |                 std::make_pair
/usr/include/c++/14/bits/stl_pair.h:1132:5: note: 'std::make_pair' declared here
 1132 |     make_pair(_T1&& __x, _T2&& __y)
      |     ^~~~~~~~~
a.cc:34:3: error: 's' was not declared in this scope
   34 |   s = s2.size();
      |   ^
a.cc:34:7: error: 's2' was not declared in this scope
   34 |   s = s2.size();
      |       ^~
a.cc:37:5: error: 'a' was not declared in this scope
   37 |     a[i] = s2.top().second;
      |     ^
a.cc:44:19: error: 'a' was not declared in this scope
   44 |     printf(" %d", a[i]);
      |                   ^