控制流程

// 基本的 if 语句
int age = 18;
if (age >= 18) {
    cout << "您已成年" << endl;
}

// if-else 语句
int score = 75;
if (score >= 60) {
    cout << "及格" << endl;
} else {
    cout << "不及格" << endl;
}

// if-else if-else 语句
int grade = 85;
if (grade >= 90) {
    cout << "优秀" << endl;
} else if (grade >= 80) {
    cout << "良好" << endl;
} else if (grade >= 60) {
    cout << "及格" << endl;
} else {
    cout << "不及格" << endl;
}

// 嵌套的 if 语句
bool hasID = true;
if (age >= 18) {
    if (hasID) {
        cout << "可以办理" << endl;
    } else {
        cout << "请先办理身份证" << endl;
    }
}

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 << "无效日期" << endl;
}

// 不使用 break 的级联效果
char grade = 'B';
switch (grade) {
    case 'A':
        cout << "优秀" << endl;
        break;
    case 'B':
    case 'C':
        cout << "良好" << endl;
        break;
    case 'D':
        cout << "及格" << endl;
        break;
    default:
        cout << "不及格" << endl;
}