CPP学习 用栈容器解决问题示例，判断括号是否成对出现

#include<string>
#include<iostream>
#include<stack>
using namespace std;
bool isbalanced(const string& str)
{
    int len = str.size();
    stack<char> mystack;
    for (int i = 0; i < len; i++)
    {
        if (str[i] == '(' || str[i] == '[' || str[i] == '{' || str[i] == '<')
            mystack.push(str[i]);//将左括号压入栈中
        if (str[i] == ')' || str[i] == ']' || str[i] == '}' || str[i] == '>')
        {
            if (mystack.empty())//如果栈为空，说明没有左括号与右括号匹配，直接返回false
            {
                cout << "The string is not balanced.You have more closing brackets than opening brackets." << endl;
                exit(0);
            }
            switch (str[i])
            {
                case ')':
                {
                    if (mystack.top() != '(')
                        return false;mystack.pop(); break;
                }
                case ']':
                {
                    if (mystack.top() != '[')
                        return false;mystack.pop(); break;
                }
                case '}':
                {
                    if (mystack.top() != '{')
                        return false;mystack.pop(); break;
                }
                case '>':
                {
                    if (mystack.top() != '<')
                        return false;mystack.pop(); break;
                }
            }
        }
    }
    if (mystack.empty())//N.empty()返回的是一个bool值
        return true;
    else
        return false;
}
int main()
{
    bool bal;string str;
    cin >> str;
    bal = isbalanced(str);//调用函数
    if (bal)
        cout << "The string is balanced." << endl;
    else
        cout << "The string is not balanced." << endl;
    return 0;
}