C++ 基础知识

#include <iostream>
using namespace std;

int main() {
    double celsius;
    cout << "请输入摄氏温度: ";
    cin >> celsius;
    double fahrenheit = celsius * 9.0 / 5 + 32;
    cout << "华氏温度: " << fahrenheit << "°F" << endl;
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    int year;
    cout << "输入年份: ";
    cin >> year;

    if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
        cout << year << " 是闰年" << endl;
    } else {
        cout << year << " 不是闰年" << endl;
    }
    return 0;
}

#include <iostream>
using namespace std;

long long factorial(int n) {
    long long result = 1;
    for (int i = 2; i <= n; i++) {
        result *= i;
    }
    return result;
}

int main() {
    int n;
    cout << "请输入 n: ";
    cin >> n;
    cout << n << "! = " << factorial(n) << endl;
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    int arr[5];
    cout << "输入5个整数:" << endl;
    for (int i = 0; i < 5; i++) cin >> arr[i];

    // 冒泡排序
    for (int i = 0; i < 4; i++) {
        for (int j = 0; j < 4 - i; j++) {
            if (arr[j] > arr[j + 1]) {
                int temp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
            }
        }
    }

    cout << "排序后: ";
    for (int n : arr) cout << n << " ";
    cout << endl;
    return 0;
}

#include <iostream>
using namespace std;

bool isPalindrome(int n) {
    if (n < 0) return false;
    long long reversed = 0, original = n;
    while (n > 0) {
        reversed = reversed * 10 + n % 10;
        n /= 10;
    }
    return original == reversed;
}

int main() {
    int n;
    cin >> n;
    cout << (isPalindrome(n) ? "是回文数" : "不是回文数") << endl;
    return 0;
}

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

struct Student {
    string name;
    int chinese, math, english;
    int total() { return chinese + math + english; }
    double avg() { return total() / 3.0; }
};

int main() {
    const int N = 3;
    Student s[N];

    for (int i = 0; i < N; i++) {
        cout << "输入学生" << i + 1 << " 姓名 语文 数学 英语: ";
        cin >> s[i].name >> s[i].chinese >> s[i].math >> s[i].english;
    }

    int maxIdx = 0;
    for (int i = 0; i < N; i++) {
        cout << s[i].name << " 总分=" << s[i].total()
             << " 平均=" << s[i].avg() << endl;
        if (s[i].total() > s[maxIdx].total()) maxIdx = i;
    }
    cout << "最高分: " << s[maxIdx].name << endl;
    return 0;
}

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

double add(double a, double b) { return a + b; }
double sub(double a, double b) { return a - b; }
double mul(double a, double b) { return a * b; }
double divi(double a, double b) {
    if (b == 0) { cout << "除零错误！"; return 0; }
    return a / b;
}

int main() {
    string op;
    double a, b;
    while (true) {
        cout << "输入操作 (+ - * / ^ % 或 exit): ";
        cin >> op;
        if (op == "exit") break;
        cout << "输入两个数: ";
        cin >> a >> b;

        if (op == "+") cout << "结果: " << add(a, b) << endl;
        else if (op == "-") cout << "结果: " << sub(a, b) << endl;
        else if (op == "*") cout << "结果: " << mul(a, b) << endl;
        else if (op == "/") cout << "结果: " << divi(a, b) << endl;
        else if (op == "^") cout << "结果: " << pow(a, b) << endl;
        else if (op == "%") cout << "结果: " << (int)a % (int)b << endl;
        else cout << "未知操作" << endl;
    }
    cout << "再见！" << endl;
    return 0;
}

#include <iostream>
#include <cstdlib>   // rand(), srand()
#include <ctime>     // time()
using namespace std;

int main() {
    srand(time(0));                    // 用当前时间做随机种子
    int secret = rand() % 100 + 1;    // 1~100
    int guess, count = 0;

    cout << "猜数字游戏！我想了一个1-100的数字。" << endl;
    while (true) {
        cout << "你的猜测: ";
        cin >> guess;
        count++;
        if (guess > secret) cout << "太大了！" << endl;
        else if (guess < secret) cout << "太小了！" << endl;
        else {
            cout << "恭喜你猜对了！答案是 " << secret
                 << "，你猜了 " << count << " 次。" << endl;
            break;
        }
    }
    return 0;
}

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

const int MAX = 100;
string tasks[MAX];
int taskCount = 0;
string filename = "todo.txt";

void load() {
    ifstream in(filename);
    taskCount = 0;
    while (taskCount < MAX && getline(in, tasks[taskCount])) {
        taskCount++;
    }
}

void save() {
    ofstream out(filename);
    for (int i = 0; i < taskCount; i++) out << tasks[i] << endl;
}

void show() {
    if (taskCount == 0) { cout << "暂无任务" << endl; return; }
    for (int i = 0; i < taskCount; i++)
        cout << i + 1 << ". " << tasks[i] << endl;
}

void add(string t) {
    if (taskCount < MAX) tasks[taskCount++] = t;
}

void remove(int idx) {
    if (idx < 1 || idx > taskCount) return;
    for (int i = idx - 1; i < taskCount - 1; i++)
        tasks[i] = tasks[i + 1];
    taskCount--;
}

int main() {
    load();
    string cmd;
    cout << "=== 待办清单 === (add/show/del/save/quit)" << endl;
    while (true) {
        cout << "> "; cin >> cmd;
        if (cmd == "quit") { save(); break; }
        else if (cmd == "show") show();
        else if (cmd == "add") {
            cin.ignore();
            string t; getline(cin, t); add(t);
        }
        else if (cmd == "del") {
            int n; cin >> n; remove(n);
        }
        else if (cmd == "save") save();
        else cout << "未知命令" << endl;
    }
    return 0;
}