Parenthesis checker is working for individual test case perfectly but for all test case together it is giving segmentation fault?

I have written code for parenthesis checker using stack in c++ ,it is working perfectly fine for all test cases individually but when i perform test case simultaneously in one go then it is giving error of segmentation fault.

       using namespace std;
      int main()
 {
    //code
    int t;
    cin>>t;
    while(t--){
      string str;
      cin>>str;

      stack<char>box;

      int len = str.size();
      box.push(str[0]);
      for(int i =1;i<len;i++){
          char temp = str[i];
          char tp = box.top();

         if(( (tp=='{' && temp=='}')  || ( tp=='[' && temp==']')  ||  (tp=='(' && temp==')') )&&(!box.empty()) ){
          // cout<<"here";

            box.pop();


         }else{
            //cout<<temp;


             box.push(temp);
         }

      }


     if(box.empty()==true)  cout<<"balanced"<<endl;
     else cout<<"not balanced"<<endl;



    }
    return 0;
```  }