стек

#include <iostream>
#include <string>
using namespace std;

struct IElem
{
   int value;
   IElem *next;
};

class IStack
{
   IElem *pbeg, *pend;
   int Size;
public:
   IStack()
   {
     pbeg = NULL;
   }
   int get_size()
   {
     return Size;
   }
   int top();
   void push(int val);
   int pop();
};

void IStack::push(int val)
{
   IElem *ptr = new IElem;
   ptr->value = val;
   ptr->next = pbeg;
   pbeg = ptr;
   Size++;
}

int IStack::pop()
{
   if (!pbeg)
    return -1;
   IElem *ptr = pbeg;
   int val = pbeg->value;
   pbeg = pbeg->next;
   delete ptr;
   return val;
}

int main()
{
  IStack stack;
  string s, time;

  int n = 1, znach = 0;

  cin >> s;
  int dlina = s.length();
  int i = 0;

  while (i < dlina && n != 0)
{
  if (s[i]=='(' || s[i]=='[' || s[i] =='{' || s[i] =='<')
    {
      stack.push(s[i]);
      znach++;
      // cout << n << " ";
    }
  else if (s[i] ==')')
   {
     if (stack.pop()=='(')
      n = 1;
    else n = 0;
    //cout << n << " ";
   }
  else if (s[i] ==']' )
    {
     if (stack.pop()=='[')
      n = 1;
      else  n = 0;
      //cout << n << " ";
    }
  else if (s[i] =='}')
    {
     if (stack.pop()=='{')
       n = 1;
      else n = 0;
      //cout << n << " ";
    }
  else if (s[i] =='>')
    {
      if (stack.pop()=='<')
       n = 1;
       else n = 0;
      // cout << n << " ";
    }
    i++;
}

cout << n;
}