求圆半径和周长

#include <iostream>
using namespace std;

struct Cir
{
private:
    int r;
public:
    void set_r(int i);
    void show();
};
void Cir::set_r(int i)//设置半径
{
    r = i;
}
void Cir::show()//打印周长面积
{
    double Pi = 3.14;
    double l = 2*Pi*r;
    double s = Pi*r*r;
    cout<< "周长=" << l << endl;
    cout<< "面积=" << s << endl;
}
int main()
{
    Cir cir;
    int i;
    cin >> i;
    cir.set_r(i);
    cir.show();
    return 0;
}

汽车

#include <iostream>
using namespace std;

struct Car
{
    string brand;
    string color;
    int speed;
    void dispaly();
    void accelerate(int amount);
    void set(string a,string b,int c);
};

void Car::dispaly()
{
    cout << "汽车信息如下:" << endl;
    cout << "品牌:" << brand <<endl;
    cout << "颜色:" << color <<endl;
    cout << "初速度:" << speed << "km/h" << endl;
}

void Car::accelerate(int amount)
{
    speed += amount;
}

void Car::set(string a,string b,int c)
{
    brand = a;
    color = b;
    speed = c;
}

int main()
{
    Car car;
    string a,b;int c;
    cin >> a >> b >> c;
    car.set(a,b,c);
    car.dispaly();
    int amount;
    cout << "请输入加速值:";
    cin >> amount;
    car.accelerate(amount);
    car.dispaly();

    return 0;
}