c++用if语句和switch多分支选择结构编写一个程序包含三个条件1.求圆面积2.求四则运算3.判断水仙花数

在C++中，你可以使用if-else语句或switch-case结构来根据不同的条件执行不同的操作。这里是一个简单的示例，它会根据用户输入的选择分别计算圆面积、执行四则运算，或者检查是否是水仙花数：

#include <iostream>
using namespace std;

double calculateCircleArea(double radius) {
    return M_PI * pow(radius, 2);
}

int performArithmetic(int a, int b, char op) {
    switch (op) {
        case '+':
            return a + b;
        case '-':
            return a - b;
        case '*':
            return a * b;
        case '/':
            if (b != 0)
                return a / b;
            else
                throw "Error: Division by zero!";
        default:
            cout << "Invalid operator" << endl;
            return 0;
    }
}

bool isPerfectNumber(int num) {
    int sum = 0;
    for (int i = 1; i * i <= num; i++) {
        if (num % i == 0) {
            sum += i;
            if (i * i != num)
                sum += num / i;
        }
    }
    return sum == num && num > 1;
}

int main() {
    int choice;
    cout << "Choose an operation:\n"
         << "1. Calculate circle area\n"
         << "2. Perform arithmetic (+,-,*,/)\n"
         << "3. Check for perfect number\n"
         << "Enter your choice: ";
    cin >> choice;

    double radius;
    int a, b;
    char op;

    switch (choice) {
        case 1:
            cout << "Enter the radius: ";
            cin >> radius;
            cout << "The area of the circle is: " << calculateCircleArea(radius) << endl;
            break;
        case 2:
            cout << "Enter two numbers and an operator (+,-,*,/): ";
            cin >> a >> b >> op;
            cout << "Result: " << performArithmetic(a, b, op) << endl;
            break;
        case 3:
            cout << "Enter a number to check for being a perfect number: ";
            cin >> num;
            if (isPerfectNumber(num))
                cout << num << " is a perfect number." << endl;
            else
                cout << num << " is not a perfect number." << endl;
            break;
        default:
            cout << "Invalid choice!" << endl;
    }

    return 0;
}