单选题库

#include <iostream>
#include <queue>
 
using namespace std;
 
bool is_front_equal(std::queue<int>& q, int a) {
    bool is_equal = false;
    if (!q.empty()) {
        ________________________  // 在此处填入代码
    }
    return is_equal;
}

#include <iostream>
#include <stack>
#include <string>
 
using namespace std;
 
bool is_valid(string s) {
    stack<char> st;
    char top;
 
    for (char& ch : s) {
        if (ch == '(' || ch == '{' || ch == '[') {
            st.push(ch);   // 左括号入栈
        }
        else {
            if (st.empty())
                return false;
            ________________________  // 在此处填入代码
            if ((ch == ')' && top != '(') ||
                (ch == '}' && top != '{') ||
                (ch == ']' && top != '[')) {
                return false;
            }
        }
    }
 
    return st.empty();   // 栈为空则说明所有括号匹配成功
}

#include <iostream>
using namespace std;
 
class Base {
private:
    int a;
protected:
    int b;
public:
    int c;
    Base() : a(1), b(2), c(3) {}
};
 
class Derived : public Base {
public:
    void show() {
        cout << a << endl;   // Line 1
        cout << b << endl;   // Line 2
        cout << c << endl;   // Line 3
    }
};