第4课: 流程控制

if语句

#include <iostream>
using namespace std;

int main() {
    int score = 85;

    // 单分支
    if (score >= 60) {
        cout << "及格" << endl;
    }

    // 双分支
    if (score >= 60) {
        cout << "及格" << endl;
    } else {
        cout << "不及格" << endl;
    }

    // 多分支
    if (score >= 90) {
        cout << "优秀" << endl;
    } else if (score >= 80) {
        cout << "良好" << endl;
    } else if (score >= 70) {
        cout << "中等" << endl;
    } else if (score >= 60) {
        cout << "及格" << endl;
    } else {
        cout << "不及格" << endl;
    }

    return 0;
}

switch语句

#include <iostream>
using namespace std;

int main() {
    int day = 3;

    switch (day) {
        case 1:
            cout << "星期一" << endl;
            break;
        case 2:
            cout << "星期二" << endl;
            break;
        case 3:
            cout << "星期三" << endl;
            break;
        case 4:
            cout << "星期四" << endl;
            break;
        case 5:
            cout << "星期五" << endl;
            break;
        case 6:
        case 7:
            cout << "周末" << endl;
            break;
        default:
            cout << "无效的日期" << endl;
    }

    return 0;
}

while循环

#include <iostream>
using namespace std;

int main() {
    // 计算1到100的和
    int sum = 0;
    int i = 1;

    while (i <= 100) {
        sum += i;
        i++;
    }

    cout << "1到100的和：" << sum << endl;

    return 0;
}

do-while循环

#include <iostream>
using namespace std;

int main() {
    int num;

    // 至少执行一次
    do {
        cout << "请输入一个正数（输入0退出）：";
        cin >> num;

        if (num > 0) {
            cout << "你输入的是：" << num << endl;
        }
    } while (num != 0);

    cout << "程序结束" << endl;

    return 0;
}

for循环

#include <iostream>
using namespace std;

int main() {
    // 打印1到10
    for (int i = 1; i <= 10; i++) {
        cout << i << " ";
    }
    cout << endl;

    // 打印九九乘法表
    for (int i = 1; i <= 9; i++) {
        for (int j = 1; j <= i; j++) {
            cout << j << "x" << i << "=" << (i*j) << "\t";
        }
        cout << endl;
    }

    return 0;
}

break和continue

#include <iostream>
using namespace std;

int main() {
    // break：跳出循环
    for (int i = 1; i <= 10; i++) {
        if (i == 5) {
            break;  // 遇到5就退出循环
        }
        cout << i << " ";
    }
    cout << endl;  // 输出：1 2 3 4

    // continue：跳过本次循环
    for (int i = 1; i <= 10; i++) {
        if (i == 5) {
            continue;  // 跳过5
        }
        cout << i << " ";
    }
    cout << endl;  // 输出：1 2 3 4 6 7 8 9 10

    return 0;
}

嵌套循环

#include <iostream>
using namespace std;

int main() {
    // 打印矩形
    for (int i = 0; i < 5; i++) {
        for (int j = 0; j < 10; j++) {
            cout << "* ";
        }
        cout << endl;
    }

    // 打印三角形
    for (int i = 1; i <= 5; i++) {
        for (int j = 1; j <= i; j++) {
            cout << "* ";
        }
        cout << endl;
    }

    return 0;
}

goto语句（不推荐使用）

#include <iostream>
using namespace std;

int main() {
    int num = 0;

start:
    num++;
    cout << num << " ";

    if (num < 5) {
        goto start;  // 跳转到start标签
    }

    cout << endl;
    return 0;
}