bool isbalance(const string &str){    string::size_type len = str.size();    stack
     
       Mystack;    for(string::size_type i = 0; i < len ; ++ i)    {                /*first selection*/         if(str[i] == '[' || str[i] == '{
    ' || str[i] == '(' || str[i] == '<')         {             Mystack.push(str[i]);         }          /*如果是对称的符号，则从栈中弹出*/         if(str[i] == ']' || str[i] == '}' || str[i] == ')' || str[i] == '>')         {             /*如果栈中没有对象，则说明不平衡*/             if(Mystack.empty())             {                 cout << "the string is Unblanced" << endl;                 return false;             }             /*采用switch-case语句判断*/             switch(str[i])             {              case ']':                 {                      /*判断是否是匹配的*/                     char tem = Mystack.top();                     Mystack.pop();                     if('[' != tem)                     {                         cout << "Can not blanced with ]" << endl;                         return false;                     }                     break;                 }             case ')':                 {                      /*判断是否是匹配的*/                     char tem = Mystack.top();                     Mystack.pop();                     if('(' != tem)                     {                         cout << "Can not blanced with )" << endl;                         return false;                     }                     break;                 }             case '}':                 {                      /*判断是否是匹配的*/                     char tem = Mystack.top();                     Mystack.pop();                     if('{
    ' != tem)                     {                         cout << "Can not blanced with }" << endl;                         return false;                     }                     break;                 }             case '>':                 {                      /*判断是否是匹配的*/                     char tem = Mystack.top();                     Mystack.pop();                     if('<' != tem)                     {                         cout << "Can not blanced with >" << endl;                         return false;                     }                     break;                 }                 /*一般的非对称字符*/             default:                 break;             }         }    }     /************************************************      *当所有对象遍历完成以后，需要判断栈中是否存在对象      *栈中为空说明是平衡的，非空则说明是非空的对象     ************************************************/    if(Mystack.empty())    {         cout << "string is blanced!!" << endl;         return true;    }    else/*没有正确的匹配,并输出具体不匹配的符号*/    {        char tem = Mystack.top();        Mystack.pop();        cout << tem << " " << "Unblance string!!" << endl;        return false;    }}